forked from luck/tmp_suning_uos_patched
d133166146
When a prospective writer takes the qrwlock locking slowpath due to the lock being held, it attempts to cmpxchg the wmode field from 0 to _QW_WAITING so that concurrent lockers also take the slowpath and queue on the spinlock accordingly, allowing the lockers to drain. Unfortunately, this isn't fair, because a fastpath writer that comes in after the lock is made available but before the _QW_WAITING flag is set can effectively jump the queue. If there is a steady stream of prospective writers, then the waiter will be held off indefinitely. This patch restores fairness by separating _QW_WAITING and _QW_LOCKED into two distinct fields: _QW_LOCKED continues to occupy the bottom byte of the lockword so that it can be cleared unconditionally when unlocking, but _QW_WAITING now occupies what used to be the bottom bit of the reader count. This then forces the slow-path for concurrent lockers. Tested-by: Waiman Long <longman@redhat.com> Tested-by: Jeremy Linton <jeremy.linton@arm.com> Tested-by: Adam Wallis <awallis@codeaurora.org> Tested-by: Jan Glauber <jglauber@cavium.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Jeremy.Linton@arm.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-arm-kernel@lists.infradead.org Link: http://lkml.kernel.org/r/1507810851-306-6-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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.. | ||
lockdep_internals.h | ||
lockdep_proc.c | ||
lockdep_states.h | ||
lockdep.c | ||
locktorture.c | ||
Makefile | ||
mcs_spinlock.h | ||
mutex-debug.c | ||
mutex-debug.h | ||
mutex.c | ||
mutex.h | ||
osq_lock.c | ||
percpu-rwsem.c | ||
qrwlock.c | ||
qspinlock_paravirt.h | ||
qspinlock_stat.h | ||
qspinlock.c | ||
rtmutex_common.h | ||
rtmutex-debug.c | ||
rtmutex-debug.h | ||
rtmutex.c | ||
rtmutex.h | ||
rwsem-spinlock.c | ||
rwsem-xadd.c | ||
rwsem.c | ||
rwsem.h | ||
semaphore.c | ||
spinlock_debug.c | ||
spinlock.c | ||
test-ww_mutex.c |