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locking/qspinlock: Re-order code 

Flip the branch condition after atomic_fetch_or_acquire(_Q_PENDING_VAL)
such that we loose the indent. This also result in a more natural code
flow IMO.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: andrea.parri@amarulasolutions.com
Cc: longman@redhat.com
Link: https://lkml.kernel.org/r/20181003130257.156322446@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2018-09-26 13:01:18 +02:00 committed by Ingo Molnar
parent ec57e2f0ac
commit 53bf57fab7
1 changed files with 27 additions and 29 deletions
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56
kernel/locking/qspinlock.c
View File

@ -330,39 +330,37 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* 0,0,1 -> 0,1,1 ; pending
*/
val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val);
if (!(val & ~_Q_LOCKED_MASK)) {
/*
* We're pending, wait for the owner to go away.
*
* *,1,1 -> *,1,0
*
* this wait loop must be a load-acquire such that we match the
* store-release that clears the locked bit and create lock
* sequentiality; this is because not all
* clear_pending_set_locked() implementations imply full
* barriers.
*/
if (val & _Q_LOCKED_MASK) {
atomic_cond_read_acquire(&lock->val,
!(VAL & _Q_LOCKED_MASK));
}
/*
* take ownership and clear the pending bit.
*
* *,1,0 -> *,0,1
*/
clear_pending_set_locked(lock);
qstat_inc(qstat_lock_pending, true);
return;
/*
* If we observe any contention; undo and queue.
*/
if (unlikely(val & ~_Q_LOCKED_MASK)) {
if (!(val & _Q_PENDING_MASK))
clear_pending(lock);
goto queue;
}
/*
* If pending was clear but there are waiters in the queue, then
* we need to undo our setting of pending before we queue ourselves.
* We're pending, wait for the owner to go away.
*
* 0,1,1 -> 0,1,0
*
* this wait loop must be a load-acquire such that we match the
* store-release that clears the locked bit and create lock
* sequentiality; this is because not all
* clear_pending_set_locked() implementations imply full
* barriers.
*/
if (!(val & _Q_PENDING_MASK))
clear_pending(lock);
if (val & _Q_LOCKED_MASK)
atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK));
/*
* take ownership and clear the pending bit.
*
* 0,1,0 -> 0,0,1
*/
clear_pending_set_locked(lock);
qstat_inc(qstat_lock_pending, true);
return;
/*
* End of pending bit optimistic spinning and beginning of MCS