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author | Linux Build Service Account <lnxbuild@quicinc.com> | 2017-07-03 07:58:00 -0700 |
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committer | Gerrit - the friendly Code Review server <code-review@localhost> | 2017-07-03 07:58:00 -0700 |
commit | fe57f5f9042a37fe9e91f9be6552b4e525c1aecd (patch) | |
tree | bdc32fbf03cc90cdee4d32eb097bb0e3b365f39e | |
parent | 1b28f2e8fb7b08168c5e356930b764ae998dbfb0 (diff) | |
parent | ba6bd90a30896933174c26e2d96d4df9acfcb75c (diff) |
Merge "osq_lock: fix osq_lock queue corruption"
-rw-r--r-- | kernel/locking/osq_lock.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 99b8d991126f..1e6a51cc25c4 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -106,6 +106,32 @@ bool osq_lock(struct optimistic_spin_queue *lock) prev = decode_cpu(old); node->prev = prev; + + /* + * We need to avoid reordering of link updation sequence of osq. + * A case in which the status of optimistic spin queue is + * CPU6->CPU2 in which CPU6 has acquired the lock. At this point + * if CPU0 comes in to acquire osq_lock, it will update the tail + * count. After tail count update if CPU2 starts to unqueue itself + * from optimistic spin queue, it will find updated tail count with + * CPU0 and update CPU2 node->next to NULL in osq_wait_next(). If + * reordering of following stores happen then prev->next where prev + * being CPU2 would be updated to point to CPU0 node: + * node->prev = prev; + * WRITE_ONCE(prev->next, node); + * + * At this point if next instruction + * WRITE_ONCE(next->prev, prev); + * in CPU2 path is committed before the update of CPU0 node->prev = + * prev then CPU0 node->prev will point to CPU6 node. At this point + * if CPU0 path's node->prev = prev is committed resulting in change + * of CPU0 prev back to CPU2 node. CPU2 node->next is NULL, so if + * CPU0 gets into unqueue path of osq_lock it will keep spinning + * in infinite loop as condition prev->next == node will never be + * true. + */ + smp_mb(); + WRITE_ONCE(prev->next, node); /* |