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Darwish" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] time/sched_clock: Use raw_read_seqcount_latch() during suspend Cc: "Ahmed S. Darwish" , "Peter Zijlstra (Intel)" , x86 , LKML In-Reply-To: <20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de> References: <20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de> MIME-Version: 1.0 Message-ID: <159975050909.20229.15551175096840400557.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/core branch of tip: Commit-ID: 58faf20a086bd34f91983609e26eac3d5fe76be3 Gitweb: https://git.kernel.org/tip/58faf20a086bd34f91983609e26eac3d5fe76be3 Author: Ahmed S. Darwish AuthorDate: Thu, 27 Aug 2020 13:40:37 +02:00 Committer: Peter Zijlstra CommitterDate: Thu, 10 Sep 2020 11:19:28 +02:00 time/sched_clock: Use raw_read_seqcount_latch() during suspend sched_clock uses seqcount_t latching to switch between two storage places protected by the sequence counter. This allows it to have interruptible, NMI-safe, seqcount_t write side critical sections. Since 7fc26327b756 ("seqlock: Introduce raw_read_seqcount_latch()"), raw_read_seqcount_latch() became the standardized way for seqcount_t latch read paths. Due to the dependent load, it has one read memory barrier less than the currently used raw_read_seqcount() API. Use raw_read_seqcount_latch() for the suspend path. Commit aadd6e5caaac ("time/sched_clock: Use raw_read_seqcount_latch()") missed changing that instance of raw_read_seqcount(). References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from NMI") Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de --- kernel/time/sched_clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index 1c03eec..8c6b5fe 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -258,7 +258,7 @@ void __init generic_sched_clock_init(void) */ static u64 notrace suspended_sched_clock_read(void) { - unsigned int seq = raw_read_seqcount(&cd.seq); + unsigned int seq = raw_read_seqcount_latch(&cd.seq); return cd.read_data[seq & 1].epoch_cyc; }