Waiman Long 6eebd5fb20 locking/rwsem: Allow slowpath writer to ignore handoff bit if not set by first waiter ... With commit d257cc8cb8 ("locking/rwsem: Make handoff bit handling more consistent"), the writer that sets the handoff bit can be interrupted out without clearing the bit if the wait queue isn't empty. This disables reader and writer optimistic lock spinning and stealing. Now if a non-first writer in the queue is somehow woken up or a new waiter enters the slowpath, it can't acquire the lock. This is not the case before commit d257cc8cb8 as the writer that set the handoff bit will clear it when exiting out via the out_nolock path. This is less efficient as the busy rwsem stays in an unlock state for a longer time. In some cases, this new behavior may cause lockups as shown in [1] and [2]. This patch allows a non-first writer to ignore the handoff bit if it is not originally set or initiated by the first waiter. This patch is shown to be effective in fixing the lockup problem reported in [1]. [1] https://lore.kernel.org/lkml/20220617134325.GC30825@techsingularity.net/ [2] https://lore.kernel.org/lkml/3f02975c-1a9d-be20-32cf-f1d8e3dfafcc@oracle.com/ Fixes: d257cc8cb8 ("locking/rwsem: Make handoff bit handling more consistent") Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: John Donnelly <john.p.donnelly@oracle.com> Tested-by: Mel Gorman <mgorman@techsingularity.net> Link: https://lore.kernel.org/r/20220622200419.778799-1-longman@redhat.com		2022-07-30 10:58:28 +02:00
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irqflag-debug.c
lock_events.c
lock_events.h
lock_events_list.h
lockdep.c
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
locktorture.c
Makefile
mcs_spinlock.h
mutex-debug.c
mutex.c
mutex.h
osq_lock.c
percpu-rwsem.c
qrwlock.c
qspinlock.c
qspinlock_paravirt.h
qspinlock_stat.h
rtmutex.c
rtmutex_api.c
rtmutex_common.h
rwbase_rt.c
rwsem.c	locking/rwsem: Allow slowpath writer to ignore handoff bit if not set by first waiter	2022-07-30 10:58:28 +02:00
semaphore.c
spinlock.c
spinlock_debug.c
spinlock_rt.c
test-ww_mutex.c
ww_mutex.h
ww_rt_mutex.c