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| author | Peter Zijlstra <peterz@infradead.org> | 2016-02-01 15:11:28 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-05-04 14:48:50 -0700 |
| commit | 23a67ddd4636584816e2dc2c6393511d55944974 (patch) | |
| tree | 11e8e17b58d2c3640fc00558b422ef5ed9fe89dc /kernel | |
| parent | 5a58f809d731c23c0b898d2021903db8dee4466f (diff) | |
| download | lwn-23a67ddd4636584816e2dc2c6393511d55944974.tar.gz lwn-23a67ddd4636584816e2dc2c6393511d55944974.zip | |
locking/mcs: Fix mcs_spin_lock() ordering
commit 920c720aa5aa3900a7f1689228fdfc2580a91e7e upstream.
Similar to commit b4b29f94856a ("locking/osq: Fix ordering of node
initialisation in osq_lock") the use of xchg_acquire() is
fundamentally broken with MCS like constructs.
Furthermore, it turns out we rely on the global transitivity of this
operation because the unlock path observes the pointer with a
READ_ONCE(), not an smp_load_acquire().
This is non-critical because the MCS code isn't actually used and
mostly serves as documentation, a stepping stone to the more complex
things we've build on top of the idea.
Reported-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: 3552a07a9c4a ("locking/mcs: Use acquire/release semantics")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/mcs_spinlock.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index 5b9102a47ea5..c835270f0c2f 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -67,7 +67,13 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) node->locked = 0; node->next = NULL; - prev = xchg_acquire(lock, node); + /* + * We rely on the full barrier with global transitivity implied by the + * below xchg() to order the initialization stores above against any + * observation of @node. And to provide the ACQUIRE ordering associated + * with a LOCK primitive. + */ + prev = xchg(lock, node); if (likely(prev == NULL)) { /* * Lock acquired, don't need to set node->locked to 1. Threads |