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* srcutorture: Print Tiny SRCU reader statisticsPaul E. McKenney2017-04-181-4/+11
| | | | | | | | The srcu_torture_stats() function is adapted to the specific srcu_struct layout traditionally used by SRCU. This commit therefore adds support for Tiny SRCU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Create a tiny SRCUPaul E. McKenney2017-04-183-1/+219
| | | | | | | | In response to automated complaints about modifications to SRCU increasing its size, this commit creates a tiny SRCU that is used in SMP=n && PREEMPT=n builds. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Crude control of expedited grace periodsPaul E. McKenney2017-04-181-38/+46
| | | | | | | | | | | | | | | SRCU's implementation of expedited grace periods has always assumed that the SRCU instance is idle when the expedited request arrives. This commit improves this a bit by maintaining a count of the number of outstanding expedited requests, thus allowing prior non-expedited grace periods accommodate these requests by shifting to expedited mode. However, any non-expedited wait already in progress will still wait for the full duration. Improved control of expedited grace periods is planned, but one step at a time. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Merge ->srcu_state into ->srcu_gp_seqPaul E. McKenney2017-04-182-20/+45
| | | | | | | | | Updating ->srcu_state and ->srcu_gp_seq will lead to extremely complex race conditions given multiple callback queues, so this commit takes advantage of the two-bit state now available in rcu_seq counters to store the state in the bottom two bits of ->srcu_gp_seq. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Allow a second bit in rcu_seq for SRCU statePaul E. McKenney2017-04-181-1/+1
| | | | | | | | This commit increases the number of reserved bits at the bottom of an rcu_seq grace-period counter from one to two, as will be needed to accommodate SRCU's three-state grace periods. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Improve rcu_seq grace-period-counter abstractionPaul E. McKenney2017-04-182-9/+29
| | | | | | | | | | | | The expedited grace-period code contains several open-coded shifts know the format of an rcu_seq grace-period counter, which is not particularly good style. This commit therefore creates a new rcu_seq_ctr() function that extracts the counter portion of the counter, and an rcu_seq_state() function that extracts the low-order state bit. This commit prepares for SRCU callback parallelization, which will require two state bits. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Fix bogus try_check_zero() commentPaul E. McKenney2017-04-181-4/+3
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Make num_rcu_lvl[] array be externalPaul E. McKenney2017-04-182-1/+2
| | | | | | | This commit makes the num_rcu_lvl[] array external so that SRCU can make use of it for initializing its upcoming srcu_node tree. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Move rcu_node traversal macros to rcu.hPaul E. McKenney2017-04-182-35/+35
| | | | | | | | | | This commit moves rcu_for_each_node_breadth_first(), rcu_for_each_nonleaf_node_breadth_first(), and rcu_for_each_leaf_node() from kernel/rcu/tree.h to kernel/rcu/rcu.h so that SRCU can access them. This commit is code-movement only. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove redundant levelcnt[] array from rcu_init_one()Paul E. McKenney2017-04-181-6/+3
| | | | | | | The levelcnt[] array is identical to num_rcu_lvl[], so this commit removes levelcnt[]. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Move rcu_init_levelspread() to rcu_tree_node.hPaul E. McKenney2017-04-184-25/+38
| | | | | | | | | This commit moves the rcu_init_levelspread() function from kernel/rcu/tree.c to kernel/rcu/rcu.h so that SRCU can access it. This is another step towards enabling SRCU to create its own combining tree. This commit is code-movement only, give or take knock-on adjustments. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Move combining-tree definitions for SRCU's benefitPaul E. McKenney2017-04-181-70/+1
| | | | | | | | | | | | | | This commit moves the C preprocessor code that defines the default shape of the rcu_node combining tree to a new include/linux/rcu_node_tree.h file as a first step towards enabling SRCU to create its own combining tree, which in turn enables SRCU to implement per-CPU callback handling, thus avoiding contention on the lock currently guarding the single list of callbacks. Note that users of SRCU still need to know the size of the srcu_struct structure, hence include/linux rather than kernel/rcu. This commit is code-movement only. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Use rcu_segcblist to track SRCU callbacksPaul E. McKenney2017-04-184-799/+38
| | | | | | | | | This commit switches SRCU from custom-built callback queues to the new rcu_segcblist structure. This change associates grace-period sequence numbers with groups of callbacks, which will be needed for efficient processing of per-CPU callbacks. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Add grace-period sequence numbersPaul E. McKenney2017-04-181-4/+23
| | | | | | | This commit adds grace-period sequence numbers, which will be used to handle mid-boot grace periods and per-CPU callback lists. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Move to state-based grace-period sequencingPaul E. McKenney2017-04-181-50/+61
| | | | | | | | | | | | | | | | | The current SRCU grace-period processing might never reach the last portion of srcu_advance_batches(). This is OK given the current implementation, as the first portion, up to the try_check_zero() following the srcu_flip() is sufficient to drive grace periods forward. However, it has the unfortunate side-effect of making it impossible to determine when a given grace period has ended, and it will be necessary to efficiently trace ends of grace periods in order to efficiently handle per-CPU SRCU callback lists. This commit therefore adds states to the SRCU grace-period processing, so that the end of a given SRCU grace period is marked by the transition to the SRCU_STATE_DONE state. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Push srcu_advance_batches() fastpath into common casePaul E. McKenney2017-04-181-20/+7
| | | | | | | | | | | | This commit simplifies the SRCU state machine by pushing the srcu_advance_batches() idle-SRCU fastpath into the common case. This is done by giving srcu_reschedule() a delay parameter, which is zero in the call from srcu_advance_batches(). This commit is a step towards numbering callbacks in order to efficiently handle per-CPU callback lists. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Fix warning in rcu_seq_end()Dmitry Vyukov2017-04-181-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_seq_end() function increments seq signifying completion of a grace period, after that checks that the seq is even and wakes _synchronize_rcu_expedited(). The _synchronize_rcu_expedited() function uses wait_event() to wait for even seq. The problem is that wait_event() can return as soon as seq becomes even without waiting for the wakeup. In such case the warning in rcu_seq_end() can falsely fire if the next expedited grace period starts before the check. Check that seq has good value before incrementing it. Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: josh@joshtriplett.org Cc: jiangshanlai@gmail.com Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- syzkaller-triggered warning: WARNING: CPU: 0 PID: 4832 at kernel/rcu/tree.c:3533 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533 CPU: 0 PID: 4832 Comm: kworker/0:3 Not tainted 4.10.0+ #276 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Workqueue: events wait_rcu_exp_gp Call Trace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 panic+0x1fb/0x412 kernel/panic.c:179 __warn+0x1c4/0x1e0 kernel/panic.c:540 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583 rcu_seq_end+0x110/0x140 kernel/rcu/tree.c:3533 rcu_exp_gp_seq_end kernel/rcu/tree_exp.h:36 [inline] rcu_exp_wait_wake+0x8a9/0x1330 kernel/rcu/tree_exp.h:517 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:559 [inline] wait_rcu_exp_gp+0x83/0xc0 kernel/rcu/tree_exp.h:570 process_one_work+0xc06/0x1c20 kernel/workqueue.c:2096 worker_thread+0x223/0x19c0 kernel/workqueue.c:2230 kthread+0x326/0x3f0 kernel/kthread.c:227 ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430 ---
* rcu: Expedited wakeups need to be fully orderedPaul E. McKenney2017-04-181-0/+2
| | | | | | | | | | | Expedited grace periods use workqueue handlers that wake up the requesters, but there is no lock mediating this wakeup. Therefore, memory barriers are required to ensure that the handler's memory references are seen by all to occur before synchronize_*_expedited() returns to its caller. Possibly detected by syzkaller. Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Move rcu_seq_start() and friends to rcu.hPaul E. McKenney2017-04-182-35/+40
| | | | | | | | | | This commit moves rcu_seq_start(), rcu_seq_end(), rcu_seq_snap(), and rcu_seq_done() from kernel/rcu/tree.c to kernel/rcu/rcu.h. This will allow SRCU to use these functions, which in turn will allow SRCU to move from a single global callback queue to a per-CPU callback queue. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add single-element dequeue functions to rcu_segcblistPaul E. McKenney2017-04-181-0/+45
| | | | | | | | | This commit adds single-element dequeue functions to rcu_segcblist. These are less efficient than using the extract and insert functions, but allow more precise debugging code. These functions are thus expected to be used only in debug builds, for example, CONFIG_PROVE_RCU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Allow early boot use of synchronize_srcu()Paul E. McKenney2017-04-181-0/+2
| | | | | | | This commit checks for pre-scheduler state, and if that early in the boot process, synchronize_srcu() and friends are no-ops. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Allow SRCU to access rcu_scheduler_activePaul E. McKenney2017-04-184-35/+40
| | | | | | | This is primarily a code-movement commit in preparation for allowing SRCU to handle early-boot SRCU grace periods. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Abstract multi-tail callback list handlingPaul E. McKenney2017-04-185-309/+780
| | | | | | | | | | | | | | | | | | RCU has only one multi-tail callback list, which is implemented via the nxtlist, nxttail, nxtcompleted, qlen_lazy, and qlen fields in the rcu_data structure, and whose operations are open-code throughout the Tree RCU implementation. This has been more or less OK in the past, but upcoming callback-list optimizations in SRCU could really use a multi-tail callback list there as well. This commit therefore abstracts the multi-tail callback list handling into a new kernel/rcu/rcu_segcblist.h file, and uses this new API. The simple head-and-tail pointer callback list is also abstracted and applied everywhere except for the NOCB callback-offload lists. (Yes, the plan is to apply them there as well, but this commit is already bigger than would be good.) Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changedPaul E. McKenney2017-04-181-5/+1
| | | | | | | | | | | | | If the RCU_EXPERT Kconfig option is not set (the default), then the RCU_FANOUT_LEAF Kconfig option will not be defined, which will cause the leaf-level rcu_node tree fanout to default to 32 on 32-bit systems and 64 on 64-bit systems. This can result in excessive lock contention. This commit therefore changes the computation of the leaf-level rcu_node tree fanout so that the result will be 16 unless an explicit Kconfig or kernel-boot setting says otherwise. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actionsPaul E. McKenney2017-04-184-17/+34
| | | | | | | | | | | | | The rcu_all_qs() and rcu_note_context_switch() do a series of checks, taking various actions to supply RCU with quiescent states, depending on the outcomes of the various checks. This is a bit much for scheduling fastpaths, so this commit creates a separate ->rcu_urgent_qs field in the rcu_dynticks structure that acts as a global guard for these checks. Thus, in the common case, rcu_all_qs() and rcu_note_context_switch() check the ->rcu_urgent_qs field, find it false, and simply return. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org>
* rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()Paul E. McKenney2017-04-182-52/+13
| | | | | | | | | | The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking that one of them still needs a quiescent state before doing an expensive atomic operation on the ->dynticks counter. However, this check reduces overhead only after a rare race condition, and increases complexity. This commit therefore removes the scan and the mechanism enabling the scan. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Pull rcu_qs_ctr into rcu_dynticks structurePaul E. McKenney2017-04-183-13/+9
| | | | | | | | The rcu_qs_ctr variable is yet another isolated per-CPU variable, so this commit pulls it into the pre-existing rcu_dynticks per-CPU structure. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Pull rcu_sched_qs_mask into rcu_dynticks structurePaul E. McKenney2017-04-182-7/+6
| | | | | | | | The rcu_sched_qs_mask variable is yet another isolated per-CPU variable, so this commit pulls it into the pre-existing rcu_dynticks per-CPU structure. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Semicolon inside RCU_TRACE() for tree.cPaul E. McKenney2017-04-181-4/+4
| | | | | | | | | | The current use of "RCU_TRACE(statement);" can cause odd bugs, especially where "statement" is a local-variable declaration, as it can leave a misplaced ";" in the source code. This commit therefore converts these to "RCU_TRACE(statement;)", which avoids the misplaced ";". Reported-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Semicolon inside RCU_TRACE() for Tiny RCUPaul E. McKenney2017-04-182-12/+12
| | | | | | | | | | The current use of "RCU_TRACE(statement);" can cause odd bugs, especially where "statement" is a local-variable declaration, as it can leave a misplaced ";" in the source code. This commit therefore converts these to "RCU_TRACE(statement;)", which avoids the misplaced ";". Reported-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Semicolon inside RCU_TRACE() for rcu.hPaul E. McKenney2017-04-181-2/+2
| | | | | | | | | | The current use of "RCU_TRACE(statement);" can cause odd bugs, especially where "statement" is a local-variable declaration, as it can leave a misplaced ";" in the source code. This commit therefore converts these to "RCU_TRACE(statement;)", which avoids the misplaced ";". Reported-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Check for tardy grace-period activity in cleanup_srcu_struct()Paul E. McKenney2017-04-181-2/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Users of SRCU are obliged to complete all grace-period activity before invoking cleanup_srcu_struct(). This means that all calls to either synchronize_srcu() or synchronize_srcu_expedited() must have returned, and all calls to call_srcu() must have returned, and the last call to call_srcu() must have been followed by a call to srcu_barrier(). Furthermore, the caller must have done something to prevent any further calls to synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu(). Therefore, if there has ever been an invocation of call_srcu() on the srcu_struct in question, the sequence of events must be as follows: 1. Prevent any further calls to call_srcu(). 2. Wait for any pre-existing call_srcu() invocations to return. 3. Invoke srcu_barrier(). 4. It is now safe to invoke cleanup_srcu_struct(). On the other hand, if there has ever been a call to synchronize_srcu() or synchronize_srcu_expedited(), the sequence of events must be as follows: 1. Prevent any further calls to synchronize_srcu() or synchronize_srcu_expedited(). 2. Wait for any pre-existing synchronize_srcu() or synchronize_srcu_expedited() invocations to return. 3. It is now safe to invoke cleanup_srcu_struct(). If there have been calls to all both types of functions (call_srcu() and either of synchronize_srcu() and synchronize_srcu_expedited()), then the caller must do the first three steps of the call_srcu() procedure above and the first two steps of the synchronize_s*() procedure above, and only then invoke cleanup_srcu_struct(). Note that cleanup_srcu_struct() does some probabilistic checks for the caller failing to follow these procedures, in which case cleanup_srcu_struct() does WARN_ON() and avoids freeing the per-CPU structures associated with the specified srcu_struct structure. Reported-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* srcu: Consolidate batch checking into rcu_all_batches_empty()Paul E. McKenney2017-04-181-8/+13
| | | | | | | | | | | The srcu_reschedule() function invokes rcu_batch_empty() on each of the four rcu_batch structures in the srcu_struct in question twice. Given that this check will also be needed in cleanup_srcu_struct(), this commit consolidates these four checks into a new rcu_all_batches_empty() function. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Maintain special bits at bottom of ->dynticks counterPaul E. McKenney2017-04-182-16/+62
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, IPIs are used to force other CPUs to invalidate their TLBs in response to a kernel virtual-memory mapping change. This works, but degrades both battery lifetime (for idle CPUs) and real-time response (for nohz_full CPUs), and in addition results in unnecessary IPIs due to the fact that CPUs executing in usermode are unaffected by stale kernel mappings. It would be better to cause a CPU executing in usermode to wait until it is entering kernel mode to do the flush, first to avoid interrupting usemode tasks and second to handle multiple flush requests with a single flush in the case of a long-running user task. This commit therefore reserves a bit at the bottom of the ->dynticks counter, which is checked upon exit from extended quiescent states. If it is set, it is cleared and then a new rcu_eqs_special_exit() macro is invoked, which, if not supplied, is an empty single-pass do-while loop. If this bottom bit is set on -entry- to an extended quiescent state, then a WARN_ON_ONCE() triggers. This bottom bit may be set using a new rcu_eqs_special_set() function, which returns true if the bit was set, or false if the CPU turned out to not be in an extended quiescent state. Please note that this function refuses to set the bit for a non-nohz_full CPU when that CPU is executing in usermode because usermode execution is tracked by RCU as a dyntick-idle extended quiescent state only for nohz_full CPUs. Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* sched/headers: Prepare for new header dependencies before moving code to ↵Ingo Molnar2017-03-023-0/+3
| | | | | | | | | | | | | | | | | | | | <linux/sched/debug.h> We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/debug.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* sched/headers: Prepare to move signal wakeup & sigpending methods from ↵Ingo Molnar2017-03-021-1/+1
| | | | | | | | | | | | | <linux/sched.h> into <linux/sched/signal.h> Fix up affected files that include this signal functionality via sched.h. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* sched/headers: Prepare for the removal of <linux/rtmutex.h> from <linux/sched.h>Ingo Molnar2017-03-021-0/+1
| | | | | | | | | | | Fix up missing #includes in other places that rely on sched.h doing that for them. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* sched/headers: Prepare for new header dependencies before moving code to ↵Ingo Molnar2017-03-021-1/+1
| | | | | | | | | | | | | | | | | | | | <linux/sched/signal.h> We are going to split <linux/sched/signal.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/signal.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* sched/headers: Prepare for new header dependencies before moving code to ↵Ingo Molnar2017-03-024-0/+4
| | | | | | | | | | | | | | | | | | <uapi/linux/sched/types.h> We are going to move scheduler ABI details to <uapi/linux/sched/types.h>, which will be used from a number of .c files. Create empty placeholder header that maps to <linux/types.h>. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* rcu: Separate the RCU synchronization types and APIs into ↵Ingo Molnar2017-03-024-3/+16
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | <linux/rcupdate_wait.h> So rcupdate.h is a pretty complex header, in particular it includes <linux/completion.h> which includes <linux/wait.h> - creating a dependency that includes <linux/wait.h> in <linux/sched.h>, which prevents the isolation of <linux/sched.h> from the derived <linux/wait.h> header. Solve part of the problem by decoupling rcupdate.h from completions: this can be done by separating out the rcu_synchronize types and APIs, and updating their usage sites. Since this is a mostly RCU-internal types this will not just simplify <linux/sched.h>'s dependencies, but will make all the hundreds of .c files that include rcupdate.h but not completions or wait.h build faster. ( For rcutiny this means that two dependent APIs have to be uninlined, but that shouldn't be much of a problem as they are rare variants. ) Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
*---. Merge branches 'doc.2017.01.15b', 'dyntick.2017.01.23a', ↵Paul E. McKenney2017-01-259-200/+297
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'fixes.2017.01.23a', 'srcu.2017.01.25a' and 'torture.2017.01.15b' into HEAD doc.2017.01.15b: Documentation updates dyntick.2017.01.23a: Dyntick tracking consolidation fixes.2017.01.23a: Miscellaneous fixes srcu.2017.01.25a: SRCU rewrite, fixes, and verification torture.2017.01.15b: Torture-test updates
| | | * srcu: Reduce probability of SRCU ->unlock_count[] counter overflowPaul E. McKenney2017-01-251-1/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Because there are no memory barriers between the srcu_flip() ->completed increment and the summation of the read-side ->unlock_count[] counters, both the compiler and the CPU can reorder the summation with the ->completed increment. If the updater is preempted long enough during this process, the read-side counters could overflow, resulting in a too-short grace period. This commit therefore adds a memory barrier just after the ->completed increment, ensuring that if the summation misses an increment of ->unlock_count[] from __srcu_read_unlock(), the next __srcu_read_lock() will see the new value of ->completed, thus bounding the number of ->unlock_count[] increments that can be missed to NR_CPUS. The actual overflow computation is more complex due to the possibility of nesting of __srcu_read_lock(). Reported-by: Lance Roy <ldr709@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * srcu: Force full grace-period orderingPaul E. McKenney2017-01-252-14/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If a process invokes synchronize_srcu(), is delayed just the right amount of time, and thus does not sleep when waiting for the grace period to complete, there is no ordering between the end of the grace period and the code following the synchronize_srcu(). Similarly, there can be a lack of ordering between the end of the SRCU grace period and callback invocation. This commit adds the necessary ordering. Reported-by: Lance Roy <ldr709@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Further smp_mb() adjustment per email with Lance Roy. ]
| | | * srcu: Implement more-efficient reader countsLance Roy2017-01-252-80/+61
| |_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | SRCU uses two per-cpu counters: a nesting counter to count the number of active critical sections, and a sequence counter to ensure that the nesting counters don't change while they are being added together in srcu_readers_active_idx_check(). This patch instead uses per-cpu lock and unlock counters. Because both counters only increase and srcu_readers_active_idx_check() reads the unlock counter before the lock counter, this achieves the same end without having to increment two different counters in srcu_read_lock(). This also saves a smp_mb() in srcu_readers_active_idx_check(). Possible bug: There is no guarantee that the lock counter won't overflow during srcu_readers_active_idx_check(), as there are no memory barriers around srcu_flip() (see comment in srcu_readers_active_idx_check() for details). However, this problem was already present before this patch. Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Lance Roy <ldr709@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Add lockdep checks to synchronous expedited primitivesPaul E. McKenney2017-01-231-0/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | The non-expedited synchronize_*rcu() primitives have lockdep checks, but their expedited counterparts lack these checks. This commit therefore adds these checks to the expedited synchronize_*rcu() primitives. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Eliminate unused expedited_normal counterPaul E. McKenney2017-01-232-3/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Expedited grace periods no longer fall back to normal grace periods in response to lock contention, given that expedited grace periods now use the rcu_node tree so as to avoid contention. This commit therfore removes the expedited_normal counter. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Fix comment in rcu_organize_nocb_kthreads()Paul E. McKenney2017-01-231-2/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It used to be that the rcuo callback-offload kthreads were spawned in rcu_organize_nocb_kthreads(), and the comment before the "for" loop says as much. However, this spawning has long since moved to the CPU-hotplug code, so this commit fixes this comment. Reported-by: Michalis Kokologiannakis <mixaskok@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Make rcu_cpu_starting() use its "cpu" argumentPaul E. McKenney2017-01-231-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_cpu_starting() function uses this_cpu_ptr() to locate the incoming CPU's rcu_data structure. This works for the boot CPU and for all CPUs onlined after rcu_init() executes (during very early boot). Currently, this is the full set of CPUs, so all is well. But if anyone ever parallelizes boot before rcu_init() time, it will fail. This commit therefore substitutes the rcu_cpu_starting() function's this_cpu_pointer() for per_cpu_ptr(), future-proofing the code and (arguably) improving readability. This commit inadvertently fixes a latent bug: If there ever had been more than just the boot CPU online at rcu_init() time, the old code would not initialize the non-boot CPUs, but rather would repeatedly initialize the boot CPU. Reported-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Add comment headers to expedited-grace-period counter functionsPaul E. McKenney2017-01-231-1/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | These functions (rcu_exp_gp_seq_start(), rcu_exp_gp_seq_end(), rcu_exp_gp_seq_snap(), and rcu_exp_gp_seq_done() seemed too obvious to comment when written, but not so much when being documented. This commit therefore adds header comments to each of them. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Don't wake rcuc/X kthreads on NOCB CPUsPaul E. McKenney2017-01-231-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Chris Friesen notice that rcuc/X kthreads were consuming CPU even on NOCB CPUs. This makes no sense because the only purpose or these kthreads is to invoke normal (non-offloaded) callbacks, of which there will never be any on NOCB CPUs. This problem was due to a bug in cpu_has_callbacks_ready_to_invoke(), which should have been checking ->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly) checking ->nxttail[RCU_DONE_TAIL]. Because ->nxttail[RCU_DONE_TAIL] is never NULL, the only effect is to cause the rcuc/X kthread to execute when it should not do so. This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL for NOCB CPUs. Reported-by: Chris Friesen <chris.friesen@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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