* [PATCH RT] seqlock: provide the same ordering semantics as mainline [not found] <20180426192258.GK12238@jcartwri.amer.corp.natinst.com> @ 2018-04-26 20:02 ` Julia Cartwright 2018-05-28 15:30 ` Sebastian Andrzej Siewior 0 siblings, 1 reply; 2+ messages in thread From: Julia Cartwright @ 2018-04-26 20:02 UTC (permalink / raw) To: Sebastian Andrzej Siewior, Thomas Gleixner Cc: Al Viro, John Ogness, Will Deacon, Peter Zijlstra, Gratian Crisan, linux-rt-users, linux-kernel, stable-rt 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 ^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH RT] seqlock: provide the same ordering semantics as mainline 2018-04-26 20:02 ` [PATCH RT] seqlock: provide the same ordering semantics as mainline Julia Cartwright @ 2018-05-28 15:30 ` Sebastian Andrzej Siewior 0 siblings, 0 replies; 2+ messages in thread From: Sebastian Andrzej Siewior @ 2018-05-28 15:30 UTC (permalink / raw) To: Julia Cartwright Cc: Thomas Gleixner, Al Viro, John Ogness, Will Deacon, Peter Zijlstra, Gratian Crisan, linux-rt-users, linux-kernel, stable-rt On 2018-04-26 15:02:03 [-0500], Julia Cartwright wrote: > 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(). I'm taking this without the READ_ONCE hunk because ACCESS_ONCE is gone since v4.15 and I had to move on in v4.16. > Fixes: e69f15cf77c23 ("seqlock: Prevent rt starvation") > Cc: stable-rt@vger.kernel.org > Signed-off-by: Julia Cartwright <julia@ni.com> Sebastian ^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-04-26 20:02 ` [PATCH RT] seqlock: provide the same ordering semantics as mainline Julia Cartwright
2018-05-28 15:30 ` Sebastian Andrzej Siewior
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