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locking/spinlock, netfilter: Fix nf_conntrack_lock() barriers

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Even with spin_unlock_wait() fixed, nf_conntrack_lock{,_all}() is
borken as it misses a bunch of memory barriers to order the whole
global vs local locks scheme.

Even x86 (and other TSO archs) are affected.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[ Updated the comments. ]
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
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: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-05-24 15:00:38 +02:00 committed by Ingo Molnar
parent be3e784498
commit b316ff783d
1 changed files with 22 additions and 1 deletions
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23
net/netfilter/nf_conntrack_core.c
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@ -83,6 +83,13 @@ void nf_conntrack_lock(spinlock_t *lock) __acquires(lock)
spin_lock(lock);
while (unlikely(nf_conntrack_locks_all)) {
spin_unlock(lock);
/*
* Order the 'nf_conntrack_locks_all' load vs. the
* spin_unlock_wait() loads below, to ensure
* that 'nf_conntrack_locks_all_lock' is indeed held:
*/
smp_rmb(); /* spin_lock(&nf_conntrack_locks_all_lock) */
spin_unlock_wait(&nf_conntrack_locks_all_lock);
spin_lock(lock);
}
@ -128,6 +135,14 @@ static void nf_conntrack_all_lock(void)
spin_lock(&nf_conntrack_locks_all_lock);
nf_conntrack_locks_all = true;
/*
* Order the above store of 'nf_conntrack_locks_all' against
* the spin_unlock_wait() loads below, such that if
* nf_conntrack_lock() observes 'nf_conntrack_locks_all'
* we must observe nf_conntrack_locks[] held:
*/
smp_mb(); /* spin_lock(&nf_conntrack_locks_all_lock) */
for (i = 0; i < CONNTRACK_LOCKS; i++) {
spin_unlock_wait(&nf_conntrack_locks[i]);
}
@ -135,7 +150,13 @@ static void nf_conntrack_all_lock(void)
static void nf_conntrack_all_unlock(void)
{
nf_conntrack_locks_all = false;
/*
* All prior stores must be complete before we clear
* 'nf_conntrack_locks_all'. Otherwise nf_conntrack_lock()
* might observe the false value but not the entire
* critical section:
*/
smp_store_release(&nf_conntrack_locks_all, false);
spin_unlock(&nf_conntrack_locks_all_lock);
}