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* kernel: add kcov code coverageDmitry Vyukov2016-03-221-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | kcov provides code coverage collection for coverage-guided fuzzing (randomized testing). Coverage-guided fuzzing is a testing technique that uses coverage feedback to determine new interesting inputs to a system. A notable user-space example is AFL (http://lcamtuf.coredump.cx/afl/). However, this technique is not widely used for kernel testing due to missing compiler and kernel support. kcov does not aim to collect as much coverage as possible. It aims to collect more or less stable coverage that is function of syscall inputs. To achieve this goal it does not collect coverage in soft/hard interrupts and instrumentation of some inherently non-deterministic or non-interesting parts of kernel is disbled (e.g. scheduler, locking). Currently there is a single coverage collection mode (tracing), but the API anticipates additional collection modes. Initially I also implemented a second mode which exposes coverage in a fixed-size hash table of counters (what Quentin used in his original patch). I've dropped the second mode for simplicity. This patch adds the necessary support on kernel side. The complimentary compiler support was added in gcc revision 231296. We've used this support to build syzkaller system call fuzzer, which has found 90 kernel bugs in just 2 months: https://github.com/google/syzkaller/wiki/Found-Bugs We've also found 30+ bugs in our internal systems with syzkaller. Another (yet unexplored) direction where kcov coverage would greatly help is more traditional "blob mutation". For example, mounting a random blob as a filesystem, or receiving a random blob over wire. Why not gcov. Typical fuzzing loop looks as follows: (1) reset coverage, (2) execute a bit of code, (3) collect coverage, repeat. A typical coverage can be just a dozen of basic blocks (e.g. an invalid input). In such context gcov becomes prohibitively expensive as reset/collect coverage steps depend on total number of basic blocks/edges in program (in case of kernel it is about 2M). Cost of kcov depends only on number of executed basic blocks/edges. On top of that, kernel requires per-thread coverage because there are always background threads and unrelated processes that also produce coverage. With inlined gcov instrumentation per-thread coverage is not possible. kcov exposes kernel PCs and control flow to user-space which is insecure. But debugfs should not be mapped as user accessible. Based on a patch by Quentin Casasnovas. [akpm@linux-foundation.org: make task_struct.kcov_mode have type `enum kcov_mode'] [akpm@linux-foundation.org: unbreak allmodconfig] [akpm@linux-foundation.org: follow x86 Makefile layout standards] Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: syzkaller <syzkaller@googlegroups.com> Cc: Vegard Nossum <vegard.nossum@oracle.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Tavis Ormandy <taviso@google.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com> Cc: Kostya Serebryany <kcc@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Kees Cook <keescook@google.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: David Drysdale <drysdale@google.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge branch 'akpm' (patches from Andrew)Linus Torvalds2016-03-161-4/+2
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Merge first patch-bomb from Andrew Morton: - some misc things - ofs2 updates - about half of MM - checkpatch updates - autofs4 update * emailed patches from Andrew Morton <akpm@linux-foundation.org>: (120 commits) autofs4: fix string.h include in auto_dev-ioctl.h autofs4: use pr_xxx() macros directly for logging autofs4: change log print macros to not insert newline autofs4: make autofs log prints consistent autofs4: fix some white space errors autofs4: fix invalid ioctl return in autofs4_root_ioctl_unlocked() autofs4: fix coding style line length in autofs4_wait() autofs4: fix coding style problem in autofs4_get_set_timeout() autofs4: coding style fixes autofs: show pipe inode in mount options kallsyms: add support for relative offsets in kallsyms address table kallsyms: don't overload absolute symbol type for percpu symbols x86: kallsyms: disable absolute percpu symbols on !SMP checkpatch: fix another left brace warning checkpatch: improve UNSPECIFIED_INT test for bare signed/unsigned uses checkpatch: warn on bare unsigned or signed declarations without int checkpatch: exclude asm volatile from complex macro check mm: memcontrol: drop unnecessary lru locking from mem_cgroup_migrate() mm: migrate: consolidate mem_cgroup_migrate() calls mm/compaction: speed up pageblock_pfn_to_page() when zone is contiguous ...
| * tags: Fix DEFINE_PER_CPU expansionsPeter Zijlstra2016-03-151-4/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | $ make tags GEN tags ctags: Warning: drivers/acpi/processor_idle.c:64: null expansion of name pattern "\1" ctags: Warning: drivers/xen/events/events_2l.c:41: null expansion of name pattern "\1" ctags: Warning: kernel/locking/lockdep.c:151: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:133: null expansion of name pattern "\1" ctags: Warning: kernel/rcu/rcutorture.c:135: null expansion of name pattern "\1" ctags: Warning: kernel/workqueue.c:323: null expansion of name pattern "\1" ctags: Warning: net/ipv4/syncookies.c:53: null expansion of name pattern "\1" ctags: Warning: net/ipv6/syncookies.c:44: null expansion of name pattern "\1" ctags: Warning: net/rds/page.c:45: null expansion of name pattern "\1" Which are all the result of the DEFINE_PER_CPU pattern: scripts/tags.sh:200: '/\<DEFINE_PER_CPU([^,]*, *\([[:alnum:]_]*\)/\1/v/' scripts/tags.sh:201: '/\<DEFINE_PER_CPU_SHARED_ALIGNED([^,]*, *\([[:alnum:]_]*\)/\1/v/' The below cures them. All except the workqueue one are within reasonable distance of the 80 char limit. TJ do you have any preference on how to fix the wq one, or shall we just not care its too long? Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: David S. Miller <davem@davemloft.net> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Tejun Heo <tj@kernel.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* | Merge branch 'smp-hotplug-for-linus' of ↵Linus Torvalds2016-03-151-33/+40
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull cpu hotplug updates from Thomas Gleixner: "This is the first part of the ongoing cpu hotplug rework: - Initial implementation of the state machine - Runs all online and prepare down callbacks on the plugged cpu and not on some random processor - Replaces busy loop waiting with completions - Adds tracepoints so the states can be followed" More detailed commentary on this work from an earlier email: "What's wrong with the current cpu hotplug infrastructure? - Asymmetry The hotplug notifier mechanism is asymmetric versus the bringup and teardown. This is mostly caused by the notifier mechanism. - Largely undocumented dependencies While some notifiers use explicitely defined notifier priorities, we have quite some notifiers which use numerical priorities to express dependencies without any documentation why. - Control processor driven Most of the bringup/teardown of a cpu is driven by a control processor. While it is understandable, that preperatory steps, like idle thread creation, memory allocation for and initialization of essential facilities needs to be done before a cpu can boot, there is no reason why everything else must run on a control processor. Before this patch series, bringup looks like this: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring the rest up - All or nothing approach There is no way to do partial bringups. That's something which is really desired because we waste e.g. at boot substantial amount of time just busy waiting that the cpu comes to life. That's stupid as we could very well do preparatory steps and the initial IPI for other cpus and then go back and do the necessary low level synchronization with the freshly booted cpu. - Minimal debuggability Due to the notifier based design, it's impossible to switch between two stages of the bringup/teardown back and forth in order to test the correctness. So in many hotplug notifiers the cancel mechanisms are either not existant or completely untested. - Notifier [un]registering is tedious To [un]register notifiers we need to protect against hotplug at every callsite. There is no mechanism that bringup/teardown callbacks are issued on the online cpus, so every caller needs to do it itself. That also includes error rollback. What's the new design? The base of the new design is a symmetric state machine, where both the control processor and the booting/dying cpu execute a well defined set of states. Each state is symmetric in the end, except for some well defined exceptions, and the bringup/teardown can be stopped and reversed at almost all states. So the bringup of a cpu will look like this in the future: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring itself up The synchronization step does not require the control cpu to wait. That mechanism can be done asynchronously via a worker or some other mechanism. The teardown can be made very similar, so that the dying cpu cleans up and brings itself down. Cleanups which need to be done after the cpu is gone, can be scheduled asynchronously as well. There is a long way to this, as we need to refactor the notion when a cpu is available. Today we set the cpu online right after it comes out of the low level bringup, which is not really correct. The proper mechanism is to set it to available, i.e. cpu local threads, like softirqd, hotplug thread etc. can be scheduled on that cpu, and once it finished all booting steps, it's set to online, so general workloads can be scheduled on it. The reverse happens on teardown. First thing to do is to forbid scheduling of general workloads, then teardown all the per cpu resources and finally shut it off completely. This patch series implements the basic infrastructure for this at the core level. This includes the following: - Basic state machine implementation with well defined states, so ordering and prioritization can be expressed. - Interfaces to [un]register state callbacks This invokes the bringup/teardown callback on all online cpus with the proper protection in place and [un]installs the callbacks in the state machine array. For callbacks which have no particular ordering requirement we have a dynamic state space, so that drivers don't have to register an explicit hotplug state. If a callback fails, the code automatically does a rollback to the previous state. - Sysfs interface to drive the state machine to a particular step. This is only partially functional today. Full functionality and therefor testability will be achieved once we converted all existing hotplug notifiers over to the new scheme. - Run all CPU_ONLINE/DOWN_PREPARE notifiers on the booting/dying processor: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu wait for boot bring itself up Signal completion to control cpu In a previous step of this work we've done a full tree mechanical conversion of all hotplug notifiers to the new scheme. The balance is a net removal of about 4000 lines of code. This is not included in this series, as we decided to take a different approach. Instead of mechanically converting everything over, we will do a proper overhaul of the usage sites one by one so they nicely fit into the symmetric callback scheme. I decided to do that after I looked at the ugliness of some of the converted sites and figured out that their hotplug mechanism is completely buggered anyway. So there is no point to do a mechanical conversion first as we need to go through the usage sites one by one again in order to achieve a full symmetric and testable behaviour" * 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits) cpu/hotplug: Document states better cpu/hotplug: Fix smpboot thread ordering cpu/hotplug: Remove redundant state check cpu/hotplug: Plug death reporting race rcu: Make CPU_DYING_IDLE an explicit call cpu/hotplug: Make wait for dead cpu completion based cpu/hotplug: Let upcoming cpu bring itself fully up arch/hotplug: Call into idle with a proper state cpu/hotplug: Move online calls to hotplugged cpu cpu/hotplug: Create hotplug threads cpu/hotplug: Split out the state walk into functions cpu/hotplug: Unpark smpboot threads from the state machine cpu/hotplug: Move scheduler cpu_online notifier to hotplug core cpu/hotplug: Implement setup/removal interface cpu/hotplug: Make target state writeable cpu/hotplug: Add sysfs state interface cpu/hotplug: Hand in target state to _cpu_up/down cpu/hotplug: Convert the hotplugged cpu work to a state machine cpu/hotplug: Convert to a state machine for the control processor cpu/hotplug: Add tracepoints ...
| * | rcu: Make CPU_DYING_IDLE an explicit callThomas Gleixner2016-03-011-33/+37
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Make the RCU CPU_DYING_IDLE callback an explicit function call, so it gets invoked at the proper place. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: linux-arch@vger.kernel.org Cc: Rik van Riel <riel@redhat.com> Cc: Rafael Wysocki <rafael.j.wysocki@intel.com> Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Sebastian Siewior <bigeasy@linutronix.de> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul Turner <pjt@google.com> Link: http://lkml.kernel.org/r/20160226182341.870167933@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | | Merge commit 'torture.2015.02.23a' into core/rcuIngo Molnar2016-03-151-0/+1
|\ \ \ | | | | | | | | | | | | Signed-off-by: Ingo Molnar <mingo@kernel.org>
| * | | rcu: Export rcu_gp_is_normal()Paul E. McKenney2016-02-231-0/+1
| |/ / | | | | | | | | | | | | | | | | | | This commit exports rcu_gp_is_normal() in order to allow it to be used by rcutorture and rcuperf. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | | Merge commit 'fixes.2015.02.23a' into core/rcuIngo Molnar2016-03-155-117/+124
|\ \ \ | |_|/ |/| | | | | | | | | | | | | | Conflicts: kernel/rcu/tree.c Signed-off-by: Ingo Molnar <mingo@kernel.org>
| * | rcu: Catch up rcu_report_qs_rdp() comment with realityPaul E. McKenney2016-02-231-6/+1
| | | | | | | | | | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcu: Make rcu/tiny_plugin.h explicitly non-modularPaul Gortmaker2016-02-231-13/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The Kconfig currently controlling compilation of this code is: init/Kconfig:config TINY_RCU init/Kconfig: bool ...meaning that it currently is not being built as a module by anyone. Lets remove the modular code that is essentially orphaned, so that when reading the code there is no doubt it is builtin-only. Since module_init translates to device_initcall in the non-modular case, the init ordering remains unchanged with this commit. We could consider moving this to an earlier initcall (subsys?) if desired. We also delete the MODULE_LICENSE tag etc. since all that information is already contained at the top of the file in the comments. Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | RCU: Privatize rcu_node::lockBoqun Feng2016-02-233-75/+96
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In patch: "rcu: Add transitivity to remaining rcu_node ->lock acquisitions" All locking operations on rcu_node::lock are replaced with the wrappers because of the need of transitivity, which indicates we should never write code using LOCK primitives alone(i.e. without a proper barrier following) on rcu_node::lock outside those wrappers. We could detect this kind of misuses on rcu_node::lock in the future by adding __private modifier on rcu_node::lock. To privatize rcu_node::lock, unlock wrappers are also needed. Replacing spinlock unlocks with these wrappers not only privatizes rcu_node::lock but also makes it easier to figure out critical sections of rcu_node. This patch adds __private modifier to rcu_node::lock and makes every access to it wrapped by ACCESS_PRIVATE(). Besides, unlock wrappers are added and raw_spin_unlock(&rnp->lock) and its friends are replaced with those wrappers. Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcu: Remove useless rcu_data_p when !PREEMPT_RCUChen Gang2016-02-232-2/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The related warning from gcc 6.0: In file included from kernel/rcu/tree.c:4630:0: kernel/rcu/tree_plugin.h:810:40: warning: ‘rcu_data_p’ defined but not used [-Wunused-const-variable] static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data; ^~~~~~~~~~ Also remove always redundant rcu_data_p in tree.c. Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcutorture: Correct no-expedite console messagesPaul E. McKenney2016-02-231-6/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | The "Disabled dynamic grace-period expediting" console message is currently printed unconditionally. This commit causes it to be output only when it is impossible to switch between normal and expedited grace periods, which was the original intent. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcu: Set rdp->gpwrap when CPU is idlePaul E. McKenney2016-02-231-3/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit #e3663b1024d1 ("rcu: Handle gpnum/completed wrap while dyntick idle") sets rdp->gpwrap on the wrong side of the "if" statement in dyntick_save_progress_counter(), that is, it sets it when the CPU is not idle instead of when it is idle. Of course, if the CPU is not idle, its rdp->gpnum won't be lagging beind the global rsp->gpnum, which means that rdp->gpwrap will never be set. This commit therefore moves this code to the proper leg of that "if" statement. This change means that the "else" cause is just "return 0" and the "then" clause ends with "return 1", so also move the "return 0" to follow the "if", dropping the "else" clause. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcu: Stop treating in-kernel CPU-bound workloads as errorsPaul E. McKenney2016-02-231-6/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 4a81e8328d379 ("Reduce overhead of cond_resched() checks for RCU") handles the error case where a nohz_full loops indefinitely in the kernel with the scheduling-clock interrupt disabled. However, this handling includes IPIing the CPU running the offending loop, which is not what we want for real-time workloads. And there are starting to be real-time CPU-bound in-kernel workloads, and these must be handled without IPIing the CPU, at least not in the common case. Therefore, this situation can no longer be dismissed as an error case. This commit therefore splits the handling out, so that the setting of bits in the per-CPU rcu_sched_qs_mask variable is done relatively early, but if the problem persists, resched_cpu() is eventually used to IPI the CPU containing the offending loop. Assuming that in-kernel CPU-bound loops used by real-time tasks contain frequent calls cond_resched_rcu_qs() (as in more than once per few tens of milliseconds), the real-time tasks will never be IPIed. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org>
| * | rcu: Update rcu_report_qs_rsp() commentPaul E. McKenney2016-02-231-5/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | | The header comment for rcu_report_qs_rsp() was obsolete, dating well before the advent of RCU grace-period kthreads. This commit therefore brings this comment back into alignment with current reality. Reported-by: Lihao Liang <lihao.liang@cs.ox.ac.uk> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * | rcu: Assign false instead of 0 for ->core_needs_qsPaul E. McKenney2016-02-231-1/+1
| |/ | | | | | | | | | | | | A zero seems to have escaped earlier true/false substitution efforts, so this commit changes 0 to false for the ->core_needs_qs boolean field. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | rcu: Use simple wait queues where possible in rcutreePaul Gortmaker2016-02-253-30/+31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-6-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | rcu: Do not call rcu_nocb_gp_cleanup() while holding rnp->lockDaniel Wagner2016-02-253-5/+18
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | rcu_nocb_gp_cleanup() is called while holding rnp->lock. Currently, this is okay because the wake_up_all() in rcu_nocb_gp_cleanup() will not enable the IRQs. lockdep is happy. By switching over using swait this is not true anymore. swake_up_all() enables the IRQs while processing the waiters. __do_softirq() can now run and will eventually call rcu_process_callbacks() which wants to grap nrp->lock. Let's move the rcu_nocb_gp_cleanup() call outside the lock before we switch over to swait. If we would hold the rnp->lock and use swait, lockdep reports following: ================================= [ INFO: inconsistent lock state ] 4.2.0-rc5-00025-g9a73ba0 #136 Not tainted --------------------------------- inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. rcu_preempt/8 [HC0[0]:SC0[0]:HE1:SE1] takes: (rcu_node_1){+.?...}, at: [<ffffffff811387c7>] rcu_gp_kthread+0xb97/0xeb0 {IN-SOFTIRQ-W} state was registered at: [<ffffffff81109b9f>] __lock_acquire+0xd5f/0x21e0 [<ffffffff8110be0f>] lock_acquire+0xdf/0x2b0 [<ffffffff81841cc9>] _raw_spin_lock_irqsave+0x59/0xa0 [<ffffffff81136991>] rcu_process_callbacks+0x141/0x3c0 [<ffffffff810b1a9d>] __do_softirq+0x14d/0x670 [<ffffffff810b2214>] irq_exit+0x104/0x110 [<ffffffff81844e96>] smp_apic_timer_interrupt+0x46/0x60 [<ffffffff81842e70>] apic_timer_interrupt+0x70/0x80 [<ffffffff810dba66>] rq_attach_root+0xa6/0x100 [<ffffffff810dbc2d>] cpu_attach_domain+0x16d/0x650 [<ffffffff810e4b42>] build_sched_domains+0x942/0xb00 [<ffffffff821777c2>] sched_init_smp+0x509/0x5c1 [<ffffffff821551e3>] kernel_init_freeable+0x172/0x28f [<ffffffff8182cdce>] kernel_init+0xe/0xe0 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 irq event stamp: 76 hardirqs last enabled at (75): [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 hardirqs last disabled at (76): [<ffffffff8184116f>] _raw_spin_lock_irq+0x1f/0x90 softirqs last enabled at (0): [<ffffffff810a8df2>] copy_process.part.26+0x602/0x1cf0 softirqs last disabled at (0): [< (null)>] (null) other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_1); <Interrupt> lock(rcu_node_1); *** DEADLOCK *** 1 lock held by rcu_preempt/8: #0: (rcu_node_1){+.?...}, at: [<ffffffff811387c7>] rcu_gp_kthread+0xb97/0xeb0 stack backtrace: CPU: 0 PID: 8 Comm: rcu_preempt Not tainted 4.2.0-rc5-00025-g9a73ba0 #136 Hardware name: Dell Inc. PowerEdge R820/066N7P, BIOS 2.0.20 01/16/2014 0000000000000000 000000006d7e67d8 ffff881fb081fbd8 ffffffff818379e0 0000000000000000 ffff881fb0812a00 ffff881fb081fc38 ffffffff8110813b 0000000000000000 0000000000000001 ffff881f00000001 ffffffff8102fa4f Call Trace: [<ffffffff818379e0>] dump_stack+0x4f/0x7b [<ffffffff8110813b>] print_usage_bug+0x1db/0x1e0 [<ffffffff8102fa4f>] ? save_stack_trace+0x2f/0x50 [<ffffffff811087ad>] mark_lock+0x66d/0x6e0 [<ffffffff81107790>] ? check_usage_forwards+0x150/0x150 [<ffffffff81108898>] mark_held_locks+0x78/0xa0 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff81108a28>] trace_hardirqs_on_caller+0x168/0x220 [<ffffffff81108aed>] trace_hardirqs_on+0xd/0x10 [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810fd1c7>] swake_up_all+0xb7/0xe0 [<ffffffff811386e1>] rcu_gp_kthread+0xab1/0xeb0 [<ffffffff811089bf>] ? trace_hardirqs_on_caller+0xff/0x220 [<ffffffff81841341>] ? _raw_spin_unlock_irq+0x41/0x60 [<ffffffff81137c30>] ? rcu_barrier+0x20/0x20 [<ffffffff810d2014>] kthread+0x104/0x120 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: linux-rt-users@vger.kernel.org Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1455871601-27484-5-git-send-email-wagi@monom.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
*---. Merge branches 'doc.2015.12.05a', 'exp.2015.12.07a', 'fixes.2015.12.07a', ↵Paul E. McKenney2015-12-077-140/+234
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'list.2015.12.04b' and 'torture.2015.12.05a' into HEAD doc.2015.12.05a: Documentation updates exp.2015.12.07a: Expedited grace-period updates fixes.2015.12.07a: Miscellaneous fixes list.2015.12.04b: Linked-list updates torture.2015.12.05a: Torture-test updates
| | | * rcutorture: Print symbolic name for ->gp_statePaul E. McKenney2015-12-052-2/+25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, ->gp_state is printed as an integer, which slows debugging. This commit therefore prints a symbolic name in addition to the integer. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Updated to fix relational operator called out by Dan Carpenter. ] [ paulmck: More "const", as suggested by Josh Triplett. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | | * rcutorture: Print symbolic name for rcu_torture_writer_statePaul E. McKenney2015-12-051-1/+23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, rcu_torture_writer_state is printed as an integer, which slows debugging. This commit therefore prints a symbolic name in addition to the integer. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: More "const", as suggested by Josh Triplett. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | | * rcutorture: Dump stack when GP kthread stallsPaul E. McKenney2015-12-051-1/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit increases debug information in the case where the grace-period kthread is being prevented from running by dumping that kthread's stack. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Split into prior commit and this commit, as suggested by Josh Triplett. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | | * rcutorture: Flag nonexistent RCU GP kthreadPaul E. McKenney2015-12-051-1/+1
| |_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | Currently, if the RCU grace-period kthread has not yet been created, in which case the starvation-check code will print zero for the state, which maps to TASK_RUNNING. This could clearly be quite confusing, so this commit prints ~0, which does not map to any legal ->state value. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Make rcu_gp_init() be bool rather than intPaul E. McKenney2015-12-071-5/+5
| | | | | | | | | | | | | | | | | | | | | | | | The return value from rcu_gp_init() is always used as a bool, so this commit makes it be a bool. Reported-by: Iftekhar Ahmed <ahmedi@oregonstate.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Move wakeup out from under rnp->lockPeter Zijlstra2015-12-071-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | This patch removes a potential deadlock hazard by moving the wake_up_process() in rcu_spawn_gp_kthread() out from under rnp->lock. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Don't redundantly disable irqs in rcu_irq_{enter,exit}()Paul E. McKenney2015-12-071-6/+26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit replaces a local_irq_save()/local_irq_restore() pair with a lockdep assertion that interrupts are already disabled. This should remove the corresponding overhead from the interrupt entry/exit fastpaths. This change was inspired by the fact that Iftekhar Ahmed's mutation testing showed that removing rcu_irq_enter()'s call to local_ird_restore() had no effect, which might indicate that interrupts were always enabled anyway. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Make cpu_needs_another_gp() be boolPaul E. McKenney2015-12-071-7/+7
| | | | | | | | | | | | | | | | | | | | | The cpu_needs_another_gp() function is currently of type int, but only returns zero or one. Bow to reality and make it be of type bool. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Eliminate unused rcu_init_one() argumentPaul E. McKenney2015-12-072-5/+4
| | | | | | | | | | | | | | | | | | | | | | | | Now that the rcu_state structure's ->rda field is compile-time initialized, there is no need to pass the per-CPU rcu_data structure into rcu_init_one(). This commit therefore eliminates this now-unused parameter. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Stop disabling interrupts in scheduler fastpathsPaul E. McKenney2015-12-042-23/+18
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We need the scheduler's fastpaths to be, well, fast, and unnecessarily disabling and re-enabling interrupts is not necessarily consistent with this goal. Especially given that there are regions of the scheduler that already have interrupts disabled. This commit therefore moves the call to rcu_note_context_switch() to one of the interrupts-disabled regions of the scheduler, and removes the now-redundant disabling and re-enabling of interrupts from rcu_note_context_switch() and the functions it calls. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Shift rcu_note_context_switch() to avoid deadlock, as suggested by Peter Zijlstra. ]
| | * rcu: Avoid tick_nohz_active checks on NOCBs CPUsPaul E. McKenney2015-12-041-5/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, rcu_prepare_for_idle() checks for tick_nohz_active, even on individual NOCBs CPUs, unless all CPUs are marked as NOCBs CPUs at build time. This check is pointless on NOCBs CPUs because they never have any callbacks posted, given that all of their callbacks are handed off to the corresponding rcuo kthread. There is a check for individually designated NOCBs CPUs, but it pointelessly follows the check for tick_nohz_active. This commit therefore moves the check for individually designated NOCBs CPUs up with the check for CONFIG_RCU_NOCB_CPU_ALL. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Fix obsolete rcu_bootup_announce_oddness() commentPaul E. McKenney2015-12-041-2/+1
| | | | | | | | | | | | | | | | | | | | | This function no longer has #ifdefs, so this commit removes the header comment calling them out. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Remove lock-acquisition loop from rcu_read_unlock_special()Paul E. McKenney2015-12-041-12/+6
| | | | | | | | | | | | | | | | | | | | | | | | Several releases have come and gone without the warning triggering, so remove the lock-acquisition loop. Retain the WARN_ON_ONCE() out of sheer paranoia. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Simplify rcu_sched_qs() control flowPaul E. McKenney2015-12-041-15/+14
| | | | | | | | | | | | | | | | | | | | | This commit applies an early-exit approach to rcu_sched_qs(), reducing the nesting level and saving a line of code. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * kernel: Make rcu/tree_trace.c explicitly non-modularPaul Gortmaker2015-12-041-16/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The Kconfig currently controlling compilation of this code is: init/Kconfig:config TREE_RCU_TRACE init/Kconfig: def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU ) ...meaning that it currently is not being built as a module by anyone. Lets remove the modular code that is essentially orphaned, so that when reading the file there is no doubt it is builtin-only. Since module_init translates to device_initcall in the non-modular case, the init ordering remains unchanged with this commit. We could consider moving this to an earlier initcall if desired. We don't replace module.h with init.h since the file already has that. We also delete the moduleparam.h include that is left over from commit 64db4cfff99c04cd5f550357edcc8780f96b54a2 (""Tree RCU": scalable classic RCU implementation") since it is not needed here either. We morph some tags like MODULE_AUTHOR into the comments at the top of the file for documentation purposes. Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Move lock_class_key to local scopePaul E. McKenney2015-12-041-4/+3
| |/ |/| | | | | | | | | | | | | | | Currently, the rcu_node_class[], rcu_fqs_class[], and rcu_exp_class[] arrays needlessly pollute the global namespace within tree.c. This commit therefore converts them to static local variables within rcu_init_one(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Remove TINY_RCU bloat from pointless boot parametersPaul E. McKenney2015-12-071-3/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_expedited, rcu_normal, and rcu_normal_after_boot kernel boot parameters are pointless in the case of TINY_RCU because in that case synchronous grace periods, both expedited and normal, are no-ops. However, these three symbols contribute several hundred bytes of bloat. This commit therefore uses CPP directives to avoid compiling this code in TINY_RCU kernels. Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| * rcu: Allow expedited grace periods to be disabled at initPaul E. McKenney2015-12-041-0/+5
| | | | | | | | | | | | | | | | | | Expedited grace periods can speed up boot, but are undesirable in aggressive real-time systems. This commit therefore introduces a kernel parameter rcupdate.rcu_normal_after_boot that disables expedited grace periods just before init is spawned. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Add rcu_normal kernel parameter to suppress expeditingPaul E. McKenney2015-12-044-1/+25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Although expedited grace periods can be quite useful, and although their OS jitter has been greatly reduced, they can still pose problems for extreme real-time workloads. This commit therefore adds a rcu_normal kernel boot parameter (which can also be manipulated via sysfs) to suppress expedited grace periods, that is, to treat requests for expedited grace periods as if they were requests for normal grace periods. If both rcu_expedited and rcu_normal are specified, rcu_normal wins. This means that if you are relying on expedited grace periods to speed up boot, you will want to specify rcu_expedited on the kernel command line, and then specify rcu_normal via sysfs once boot completes. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Add more diagnostics to expedited stall warning messages.Paul E. McKenney2015-12-041-3/+21
| | | | | | | | | | | | | | | | This commit adds print statements that check the rcu_node structure to find which ->expmask bits and which ->exp_tasks structures are blocking the current expedited grace period. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Make expedited grace periods resolve stall-warning tiesPaul E. McKenney2015-12-041-1/+1
| | | | | | | | | | | | | | | | | | Currently, if a grace period ends just as the stall-warning timeout fires, an empty stall warning will be printed. This is not helpful, so this commit avoids these useless warnings by rechecking completion after awakening in synchronize_sched_expedited_wait(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Reduce expedited GP memory contention via per-CPU variablesPaul E. McKenney2015-12-043-16/+21
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, the piggybacked-work checks carried out by sync_exp_work_done() atomically increment a small set of variables (the ->expedited_workdone0, ->expedited_workdone1, ->expedited_workdone2, ->expedited_workdone3 fields in the rcu_state structure), which will form a memory-contention bottleneck given a sufficiently large number of CPUs concurrently invoking either synchronize_rcu_expedited() or synchronize_sched_expedited(). This commit therefore moves these for fields to the per-CPU rcu_data structure, eliminating the memory contention. The show_rcuexp() function also changes to sum up each field in the rcu_data structures. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Invert sync_rcu_exp_select_cpus() "if" statementPaul E. McKenney2015-12-041-16/+14
| | | | | | | | | | | | | | | | This commit saves a couple lines of code and reduces indentation by inverting the sense of an "if" statement in the function sync_rcu_exp_select_cpus(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Move smp_mb() from rcu_seq_snap() to rcu_exp_gp_seq_snap()Paul E. McKenney2015-12-041-1/+1
| | | | | | | | | | | | | | | | The memory barrier in rcu_seq_snap() is needed only for grace periods, so this commit moves it to the grace-period-oriented wrapper rcu_exp_gp_seq_snap(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Clarify role of ->expmaskinitnextPaul E. McKenney2015-12-041-0/+2
| | | | | | | | | | | | | | | | | | | | Analogy with the ->qsmaskinitnext field might lead one to believe that ->expmaskinitnext tracks online CPUs. This belief is incorrect: Any CPU that has ever been online will have its bit set in the ->expmaskinitnext field. This commit therefore adds a comment to make this clear, at least to people who read comments. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Short-circuit synchronize_sched_expedited() if only one CPUPaul E. McKenney2015-12-041-0/+4
|/ | | | | | | | If there is only one CPU, then invoking synchronize_sched_expedited() is by definition a grace period. This commit checks for this condition and does a short-circuit return in that case. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add transitivity to remaining rcu_node ->lock acquisitionsPaul E. McKenney2015-11-233-14/+14
| | | | | | | | | | | The rule is that all acquisitions of the rcu_node structure's ->lock must provide transitivity: The lock is not acquired that frequently, and sorting out exactly which required it and which did not would be a maintenance nightmare. This commit therefore supplies the needed transitivity to the remaining ->lock acquisitions. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Create transitive rnp->lock acquisition functionsPeter Zijlstra2015-11-233-64/+71
| | | | | | | | | | | | | Providing RCU's memory-ordering guarantees requires that the rcu_node tree's locking provide transitive memory ordering, which the Linux kernel's spinlocks currently do not provide unless smp_mb__after_unlock_lock() is used. Having a separate smp_mb__after_unlock_lock() after each and every lock acquisition is error-prone, hard to read, and a bit annoying, so this commit provides wrapper functions that pull in the smp_mb__after_unlock_lock() invocations. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*---. Merge branches 'doc.2015.10.06a', 'percpu-rwsem.2015.10.06a' and ↵Paul E. McKenney2015-10-073-7/+228
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'torture.2015.10.06a' into HEAD doc.2015.10.06a: Documentation updates. percpu-rwsem.2015.10.06a: Optimization of per-CPU reader-writer semaphores. torture.2015.10.06a: Torture-test updates.
| | | * rcutorture: Fix unused-function warning for torturing_tasks()Paul E. McKenney2015-10-061-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The torturing_tasks() function is used only in kernels built with CONFIG_PROVE_RCU=y, so the second definition can result in unused-function compiler warnings. This commit adds __maybe_unused to suppress these warnings. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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