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locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath()

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Queued spinlocks are not used by DEC Alpha, and furthermore operations
such as READ_ONCE() and release/relaxed RMW atomics are being changed
to imply smp_read_barrier_depends().  This commit therefore removes the
now-redundant smp_read_barrier_depends() from queued_spin_lock_slowpath(),
and adjusts the comments accordingly.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
This commit is contained in:
Paul E. McKenney
2017-10-09 11:22:50 -07:00
parent 5c6338b487
commit 548095dea6
1 changed files with 5 additions and 7 deletions
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12
kernel/locking/qspinlock.c
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@ -170,7 +170,7 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
* @tail : The new queue tail code word * @tail : The new queue tail code word
* Return: The previous queue tail code word * Return: The previous queue tail code word
* *
* xchg(lock, tail) * xchg(lock, tail), which heads an address dependency
* *
* p,*,* -> n,*,* ; prev = xchg(lock, node) * p,*,* -> n,*,* ; prev = xchg(lock, node)
*/ */
@ -409,13 +409,11 @@ queue:
if (old & _Q_TAIL_MASK) { if (old & _Q_TAIL_MASK) {
prev = decode_tail(old); prev = decode_tail(old);
/* /*
* The above xchg_tail() is also a load of @lock which generates, * The above xchg_tail() is also a load of @lock which
* through decode_tail(), a pointer. * generates, through decode_tail(), a pointer. The address
* * dependency matches the RELEASE of xchg_tail() such that
* The address dependency matches the RELEASE of xchg_tail() * the subsequent access to @prev happens after.
* such that the access to @prev must happen after.
*/ */
smp_read_barrier_depends();
WRITE_ONCE(prev->next, node); WRITE_ONCE(prev->next, node);