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| author | Yunsheng Lin <linyunsheng@huawei.com> | 2021-06-17 09:04:14 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-14 16:56:24 +0200 |
| commit | e7c3ae47978f97f528d95b0c86de51896e78d9f0 (patch) | |
| tree | b88ffda017907aeb8fe7bd56da615ab3db21b7d1 | |
| parent | ca9b5ab7910cdc4dd02219ebfe7e468709bbafac (diff) | |
| download | linux-stable-e7c3ae47978f97f528d95b0c86de51896e78d9f0.tar.gz linux-stable-e7c3ae47978f97f528d95b0c86de51896e78d9f0.tar.bz2 linux-stable-e7c3ae47978f97f528d95b0c86de51896e78d9f0.zip | |
net: sched: add barrier to ensure correct ordering for lockless qdisc
[ Upstream commit 89837eb4b2463c556a123437f242d6c2bc62ce81 ]
The spin_trylock() was assumed to contain the implicit
barrier needed to ensure the correct ordering between
STATE_MISSED setting/clearing and STATE_MISSED checking
in commit a90c57f2cedd ("net: sched: fix packet stuck
problem for lockless qdisc").
But it turns out that spin_trylock() only has load-acquire
semantic, for strongly-ordered system(like x86), the compiler
barrier implicitly contained in spin_trylock() seems enough
to ensure the correct ordering. But for weakly-orderly system
(like arm64), the store-release semantic is needed to ensure
the correct ordering as clear_bit() and test_bit() is store
operation, see queued_spin_lock().
So add the explicit barrier to ensure the correct ordering
for the above case.
Fixes: a90c57f2cedd ("net: sched: fix packet stuck problem for lockless qdisc")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | include/net/sch_generic.h | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 4dd2c9e34976..f8631ad3c868 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -163,6 +163,12 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) if (spin_trylock(&qdisc->seqlock)) goto nolock_empty; + /* Paired with smp_mb__after_atomic() to make sure + * STATE_MISSED checking is synchronized with clearing + * in pfifo_fast_dequeue(). + */ + smp_mb__before_atomic(); + /* If the MISSED flag is set, it means other thread has * set the MISSED flag before second spin_trylock(), so * we can return false here to avoid multi cpus doing @@ -180,6 +186,12 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) */ set_bit(__QDISC_STATE_MISSED, &qdisc->state); + /* spin_trylock() only has load-acquire semantic, so use + * smp_mb__after_atomic() to ensure STATE_MISSED is set + * before doing the second spin_trylock(). + */ + smp_mb__after_atomic(); + /* Retry again in case other CPU may not see the new flag * after it releases the lock at the end of qdisc_run_end(). */ |