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authorLinus Torvalds <torvalds@linux-foundation.org>2017-02-21 00:23:30 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-21 00:23:30 +0300
commit42e1b14b6e1455ece2ccbe474c25388d0230a590 (patch)
tree7f62d95f795a2ac5c183248dce39e75340ccfb76 /Documentation
parent828cad8ea05d194d8a9452e0793261c2024c23a2 (diff)
parent95cb64c1fe61e70685a95f6260c8e9cd219fe08c (diff)
downloadlinux-42e1b14b6e1455ece2ccbe474c25388d0230a590.tar.xz
Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar: "The main changes in this cycle were: - Implement wraparound-safe refcount_t and kref_t types based on generic atomic primitives (Peter Zijlstra) - Improve and fix the ww_mutex code (Nicolai Hähnle) - Add self-tests to the ww_mutex code (Chris Wilson) - Optimize percpu-rwsems with the 'rcuwait' mechanism (Davidlohr Bueso) - Micro-optimize the current-task logic all around the core kernel (Davidlohr Bueso) - Tidy up after recent optimizations: remove stale code and APIs, clean up the code (Waiman Long) - ... plus misc fixes, updates and cleanups" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (50 commits) fork: Fix task_struct alignment locking/spinlock/debug: Remove spinlock lockup detection code lockdep: Fix incorrect condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS lkdtm: Convert to refcount_t testing kref: Implement 'struct kref' using refcount_t refcount_t: Introduce a special purpose refcount type sched/wake_q: Clarify queue reinit comment sched/wait, rcuwait: Fix typo in comment locking/mutex: Fix lockdep_assert_held() fail locking/rtmutex: Flip unlikely() branch to likely() in __rt_mutex_slowlock() locking/rwsem: Reinit wake_q after use locking/rwsem: Remove unnecessary atomic_long_t casts jump_labels: Move header guard #endif down where it belongs locking/atomic, kref: Implement kref_put_lock() locking/ww_mutex: Turn off __must_check for now locking/atomic, kref: Avoid more abuse locking/atomic, kref: Use kref_get_unless_zero() more locking/atomic, kref: Kill kref_sub() locking/atomic, kref: Add kref_read() locking/atomic, kref: Add KREF_INIT() ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/locking/ww-mutex-design.txt12
1 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/locking/ww-mutex-design.txt b/Documentation/locking/ww-mutex-design.txt
index 8a112dc304c3..34c3a1b50b9a 100644
--- a/Documentation/locking/ww-mutex-design.txt
+++ b/Documentation/locking/ww-mutex-design.txt
@@ -309,11 +309,15 @@ Design:
normal mutex locks, which are far more common. As such there is only a small
increase in code size if wait/wound mutexes are not used.
+ We maintain the following invariants for the wait list:
+ (1) Waiters with an acquire context are sorted by stamp order; waiters
+ without an acquire context are interspersed in FIFO order.
+ (2) Among waiters with contexts, only the first one can have other locks
+ acquired already (ctx->acquired > 0). Note that this waiter may come
+ after other waiters without contexts in the list.
+
In general, not much contention is expected. The locks are typically used to
- serialize access to resources for devices. The only way to make wakeups
- smarter would be at the cost of adding a field to struct mutex_waiter. This
- would add overhead to all cases where normal mutexes are used, and
- ww_mutexes are generally less performance sensitive.
+ serialize access to resources for devices.
Lockdep:
Special care has been taken to warn for as many cases of api abuse