Messages in this thread Patch in this message | | | From | Julia Cartwright <> | Subject | [PATCH RT] seqlock: provide the same ordering semantics as mainline | Date | Thu, 26 Apr 2018 15:02:03 -0500 |
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The mainline implementation of read_seqbegin() orders prior loads w.r.t. the read-side critical section. Fixup the RT writer-boosting implementation to provide the same guarantee.
Also, while we're here, update the usage of ACCESS_ONCE() to use READ_ONCE().
Fixes: e69f15cf77c23 ("seqlock: Prevent rt starvation") Cc: stable-rt@vger.kernel.org Signed-off-by: Julia Cartwright <julia@ni.com> --- Found during code inspection of the RT seqlock implementation.
Julia
include/linux/seqlock.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index a59751276b94..597ce5a9e013 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -453,7 +453,7 @@ static inline unsigned read_seqbegin(seqlock_t *sl) unsigned ret; repeat: - ret = ACCESS_ONCE(sl->seqcount.sequence); + ret = READ_ONCE(sl->seqcount.sequence); if (unlikely(ret & 1)) { /* * Take the lock and let the writer proceed (i.e. evtl @@ -462,6 +462,7 @@ static inline unsigned read_seqbegin(seqlock_t *sl) spin_unlock_wait(&sl->lock); goto repeat; } + smp_rmb(); return ret; } #endif -- 2.16.1
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