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* [PATCH AUTOSEL 4.19 01/23] locking/mutex: Fix HANDOFF condition
@ 2021-09-06  1:23 Sasha Levin
  2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 02/23] regmap: fix the offset of register error log Sasha Levin
                   ` (21 more replies)
  0 siblings, 22 replies; 23+ messages in thread
From: Sasha Levin @ 2021-09-06  1:23 UTC (permalink / raw)
  To: linux-kernel, stable; +Cc: Peter Zijlstra, Yanfei Xu, Waiman Long, Sasha Levin

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit 048661a1f963e9517630f080687d48af79ed784c ]

Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:

  if (ww_ctx || !first)
    first = __mutex_waiter_is_first(lock, &waiter);
  if (first)
    __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);

But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.

Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/locking/mutex.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 354151fef06a..fbc62d360419 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -911,7 +911,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 {
 	struct mutex_waiter waiter;
-	bool first = false;
 	struct ww_mutex *ww;
 	int ret;
 
@@ -986,6 +985,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 
 	set_current_state(state);
 	for (;;) {
+		bool first;
+
 		/*
 		 * Once we hold wait_lock, we're serialized against
 		 * mutex_unlock() handing the lock off to us, do a trylock
@@ -1014,15 +1015,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		spin_unlock(&lock->wait_lock);
 		schedule_preempt_disabled();
 
-		/*
-		 * ww_mutex needs to always recheck its position since its waiter
-		 * list is not FIFO ordered.
-		 */
-		if (ww_ctx || !first) {
-			first = __mutex_waiter_is_first(lock, &waiter);
-			if (first)
-				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
-		}
+		first = __mutex_waiter_is_first(lock, &waiter);
+		if (first)
+			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
 
 		set_current_state(state);
 		/*
-- 
2.30.2


^ permalink raw reply related	[flat|nested] 23+ messages in thread
end of thread, other threads:[~2021-09-06  1:36 UTC | newest]

Thread overview: 23+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-06  1:23 [PATCH AUTOSEL 4.19 01/23] locking/mutex: Fix HANDOFF condition Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 02/23] regmap: fix the offset of register error log Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 03/23] crypto: mxs-dcp - Check for DMA mapping errors Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 04/23] sched/deadline: Fix reset_on_fork reporting of DL tasks Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 05/23] power: supply: axp288_fuel_gauge: Report register-address on readb / writeb errors Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 06/23] crypto: omap-sham - clear dma flags only after omap_sham_update_dma_stop() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 07/23] sched/deadline: Fix missing clock update in migrate_task_rq_dl() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 08/23] posix-cpu-timers: Force next expiration recalc after itimer reset Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 09/23] hrtimer: Avoid double reprogramming in __hrtimer_start_range_ns() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 10/23] udf: Check LVID earlier Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 11/23] isofs: joliet: Fix iocharset=utf8 mount option Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 12/23] bcache: add proper error unwinding in bcache_device_init Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 13/23] nvme-rdma: don't update queue count when failing to set io queues Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 14/23] power: supply: max17042_battery: fix typo in MAx17042_TOFF Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 15/23] s390/cio: add dev_busid sysfs entry for each subchannel Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 16/23] libata: fix ata_host_start() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 17/23] crypto: qat - do not ignore errors from enable_vf2pf_comms() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 18/23] crypto: qat - handle both source of interrupt in VF ISR Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 19/23] crypto: qat - fix reuse of completion variable Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 20/23] crypto: qat - fix naming for init/shutdown VF to PF notifications Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 21/23] crypto: qat - do not export adf_iov_putmsg() Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 22/23] fcntl: fix potential deadlock for &fasync_struct.fa_lock Sasha Levin
2021-09-06  1:23 ` [PATCH AUTOSEL 4.19 23/23] udf_get_extendedattr() had no boundary checks Sasha Levin

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