Revert "osq_lock: fix osq_lock queue corruption"
This reverts commit ba6bd90a30
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Perparing for taking more optimized patch suggested to upstream
for using smp_wmb() instead of smp_mb().
Change-Id: Idc4fbd884055d9a8f65f102862dd276abe54699d
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
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1 changed files with 0 additions and 26 deletions
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@ -106,32 +106,6 @@ bool osq_lock(struct optimistic_spin_queue *lock)
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prev = decode_cpu(old);
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node->prev = prev;
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/*
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* We need to avoid reordering of link updation sequence of osq.
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* A case in which the status of optimistic spin queue is
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* CPU6->CPU2 in which CPU6 has acquired the lock. At this point
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* if CPU0 comes in to acquire osq_lock, it will update the tail
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* count. After tail count update if CPU2 starts to unqueue itself
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* from optimistic spin queue, it will find updated tail count with
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* CPU0 and update CPU2 node->next to NULL in osq_wait_next(). If
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* reordering of following stores happen then prev->next where prev
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* being CPU2 would be updated to point to CPU0 node:
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* node->prev = prev;
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* WRITE_ONCE(prev->next, node);
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*
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* At this point if next instruction
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* WRITE_ONCE(next->prev, prev);
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* in CPU2 path is committed before the update of CPU0 node->prev =
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* prev then CPU0 node->prev will point to CPU6 node. At this point
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* if CPU0 path's node->prev = prev is committed resulting in change
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* of CPU0 prev back to CPU2 node. CPU2 node->next is NULL, so if
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* CPU0 gets into unqueue path of osq_lock it will keep spinning
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* in infinite loop as condition prev->next == node will never be
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* true.
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*/
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smp_mb();
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WRITE_ONCE(prev->next, node);
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/*
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