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author | Linus Torvalds <torvalds@linux-foundation.org> | 2010-10-21 12:54:12 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-10-21 12:54:12 -0700 |
commit | 888a6f77e0418b049f83d37547c209b904d30af4 (patch) | |
tree | 42cdb9f781d2177e6b380e69a66a27ec7705f51f /Documentation/RCU/checklist.txt | |
parent | 31b7eab27a314b153d8fa07ba9e9ec00a98141e1 (diff) | |
parent | 6506cf6ce68d78a5470a8360c965dafe8e4b78e3 (diff) | |
download | op-kernel-dev-888a6f77e0418b049f83d37547c209b904d30af4.zip op-kernel-dev-888a6f77e0418b049f83d37547c209b904d30af4.tar.gz |
Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (52 commits)
sched: fix RCU lockdep splat from task_group()
rcu: using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
sched: suppress RCU lockdep splat in task_fork_fair
net: suppress RCU lockdep false positive in sock_update_classid
rcu: move check from rcu_dereference_bh to rcu_read_lock_bh_held
rcu: Add advice to PROVE_RCU_REPEATEDLY kernel config parameter
rcu: Add tracing data to support queueing models
rcu: fix sparse errors in rcutorture.c
rcu: only one evaluation of arg in rcu_dereference_check() unless sparse
kernel: Remove undead ifdef CONFIG_DEBUG_LOCK_ALLOC
rcu: fix _oddness handling of verbose stall warnings
rcu: performance fixes to TINY_PREEMPT_RCU callback checking
rcu: upgrade stallwarn.txt documentation for CPU-bound RT processes
vhost: add __rcu annotations
rcu: add comment stating that list_empty() applies to RCU-protected lists
rcu: apply TINY_PREEMPT_RCU read-side speedup to TREE_PREEMPT_RCU
rcu: combine duplicate code, courtesy of CONFIG_PREEMPT_RCU
rcu: Upgrade srcu_read_lock() docbook about SRCU grace periods
rcu: document ways of stalling updates in low-memory situations
rcu: repair code-duplication FIXMEs
...
Diffstat (limited to 'Documentation/RCU/checklist.txt')
-rw-r--r-- | Documentation/RCU/checklist.txt | 46 |
1 files changed, 39 insertions, 7 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 790d1a8..0c134f8 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome! include: a. Keeping a count of the number of data-structure elements - used by the RCU-protected data structure, including those - waiting for a grace period to elapse. Enforce a limit - on this number, stalling updates as needed to allow - previously deferred frees to complete. - - Alternatively, limit only the number awaiting deferred - free rather than the total number of elements. + used by the RCU-protected data structure, including + those waiting for a grace period to elapse. Enforce a + limit on this number, stalling updates as needed to allow + previously deferred frees to complete. Alternatively, + limit only the number awaiting deferred free rather than + the total number of elements. + + One way to stall the updates is to acquire the update-side + mutex. (Don't try this with a spinlock -- other CPUs + spinning on the lock could prevent the grace period + from ever ending.) Another way to stall the updates + is for the updates to use a wrapper function around + the memory allocator, so that this wrapper function + simulates OOM when there is too much memory awaiting an + RCU grace period. There are of course many other + variations on this theme. b. Limiting update rate. For example, if updates occur only once per hour, then no explicit rate limiting is required, @@ -365,3 +374,26 @@ over a rather long period of time, but improvements are always welcome! and the compiler to freely reorder code into and out of RCU read-side critical sections. It is the responsibility of the RCU update-side primitives to deal with this. + +17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and + the __rcu sparse checks to validate your RCU code. These + can help find problems as follows: + + CONFIG_PROVE_RCU: check that accesses to RCU-protected data + structures are carried out under the proper RCU + read-side critical section, while holding the right + combination of locks, or whatever other conditions + are appropriate. + + CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the + same object to call_rcu() (or friends) before an RCU + grace period has elapsed since the last time that you + passed that same object to call_rcu() (or friends). + + __rcu sparse checks: tag the pointer to the RCU-protected data + structure with __rcu, and sparse will warn you if you + access that pointer without the services of one of the + variants of rcu_dereference(). + + These debugging aids can help you find problems that are + otherwise extremely difficult to spot. |