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Tue, 17 Dec 2024 18:18:02 -0500 (EST) From: Daniel Xu To: mingo@redhat.com, will@kernel.org, peterz@infradead.org Cc: longman@redhat.com, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, paulmck@kernel.org Subject: [PATCH] seqlock: Use WRITE_ONCE() when updating sequence Date: Tue, 17 Dec 2024 15:17:36 -0800 Message-ID: <0eaea03ecc9df536649763cfecda356fc38b6938.1734477414.git.dxu@dxuuu.xyz> X-Mailer: git-send-email 2.47.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" `sequence` is a concurrently accessed shared variable on the reader side. Therefore, it needs to be wrapped in WRITE_ONCE() in order to prevent unwanted compiler optimizations like store tearing. Signed-off-by: Daniel Xu Reviewed-by: Paul E. McKenney --- include/linux/seqlock.h | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 5298765d6ca4..f4c6f2507742 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -45,7 +45,7 @@ static inline void __seqcount_init(seqcount_t *s, const c= har *name, * Make sure we are not reinitializing a held lock: */ lockdep_init_map(&s->dep_map, name, key, 0); - s->sequence =3D 0; + WRITE_ONCE(s->sequence, 0); } =20 #ifdef CONFIG_DEBUG_LOCK_ALLOC @@ -405,7 +405,7 @@ do { \ static inline void do_raw_write_seqcount_begin(seqcount_t *s) { kcsan_nestable_atomic_begin(); - s->sequence++; + WRITE_ONCE(s->sequence, READ_ONCE(s->sequence) + 1); smp_wmb(); } =20 @@ -426,7 +426,7 @@ do { \ static inline void do_raw_write_seqcount_end(seqcount_t *s) { smp_wmb(); - s->sequence++; + WRITE_ONCE(s->sequence, READ_ONCE(s->sequence) + 1); kcsan_nestable_atomic_end(); } =20 @@ -548,9 +548,9 @@ static inline void do_write_seqcount_end(seqcount_t *s) static inline void do_raw_write_seqcount_barrier(seqcount_t *s) { kcsan_nestable_atomic_begin(); - s->sequence++; + WRITE_ONCE(s->sequence, READ_ONCE(s->sequence) + 1); smp_wmb(); - s->sequence++; + WRITE_ONCE(s->sequence, READ_ONCE(s->sequence) + 1); kcsan_nestable_atomic_end(); } =20 @@ -569,7 +569,7 @@ static inline void do_write_seqcount_invalidate(seqcoun= t_t *s) { smp_wmb(); kcsan_nestable_atomic_begin(); - s->sequence+=3D2; + WRITE_ONCE(s->sequence, READ_ONCE(s->sequence) + 2); kcsan_nestable_atomic_end(); } =20 @@ -673,7 +673,7 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, un= signed start) static __always_inline void raw_write_seqcount_latch(seqcount_latch_t *s) { smp_wmb(); /* prior stores before incrementing "sequence" */ - s->seqcount.sequence++; + WRITE_ONCE(s->seqcount.sequence, READ_ONCE(s->seqcount.sequence) + 1); smp_wmb(); /* increment "sequence" before following stores */ } =20 --=20 2.47.0