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From: Leo Yan <leo.yan@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	"Ben Dooks (Codethink)" <ben.dooks@codethink.co.uk>,
	Paul Cercueil <paul@crapouillou.net>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Cc: Leo Yan <leo.yan@linaro.org>
Subject: [PATCH v3 2/7] time/sched_clock: Use raw_read_seqcount_latch()
Date: Thu, 16 Jul 2020 13:11:25 +0800	[thread overview]
Message-ID: <20200716051130.4359-3-leo.yan@linaro.org> (raw)
In-Reply-To: <20200716051130.4359-1-leo.yan@linaro.org>

From: "Ahmed S. Darwish" <a.darwish@linutronix.de>

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 also has one read
memory barrier less than the currently used raw_read_seqcount() API.

Use raw_read_seqcount_latch() for the seqcount_t latch read path.

Link: https://lkml.kernel.org/r/20200625085745.GD117543@hirez.programming.kicks-ass.net
Link: https://lkml.kernel.org/r/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de
References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from NMI")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 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 0acaadc3156c..0deaf4b79fb4 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -70,7 +70,7 @@ static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 
 struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
 {
-	*seq = raw_read_seqcount(&cd.seq);
+	*seq = raw_read_seqcount_latch(&cd.seq);
 	return cd.read_data + (*seq & 1);
 }
 
-- 
2.17.1


WARNING: multiple messages have this Message-ID (diff)
From: Leo Yan <leo.yan@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	"Ben Dooks (Codethink)" <ben.dooks@codethink.co.uk>,
	Paul Cercueil <paul@crapouillou.net>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Cc: Leo Yan <leo.yan@linaro.org>
Subject: [PATCH v3 2/7] time/sched_clock: Use raw_read_seqcount_latch()
Date: Thu, 16 Jul 2020 13:11:25 +0800	[thread overview]
Message-ID: <20200716051130.4359-3-leo.yan@linaro.org> (raw)
In-Reply-To: <20200716051130.4359-1-leo.yan@linaro.org>

From: "Ahmed S. Darwish" <a.darwish@linutronix.de>

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 also has one read
memory barrier less than the currently used raw_read_seqcount() API.

Use raw_read_seqcount_latch() for the seqcount_t latch read path.

Link: https://lkml.kernel.org/r/20200625085745.GD117543@hirez.programming.kicks-ass.net
Link: https://lkml.kernel.org/r/20200715092345.GA231464@debian-buster-darwi.lab.linutronix.de
References: 1809bfa44e10 ("timers, sched/clock: Avoid deadlock during read from NMI")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 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 0acaadc3156c..0deaf4b79fb4 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -70,7 +70,7 @@ static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 
 struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
 {
-	*seq = raw_read_seqcount(&cd.seq);
+	*seq = raw_read_seqcount_latch(&cd.seq);
 	return cd.read_data + (*seq & 1);
 }
 
-- 
2.17.1


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  parent reply	other threads:[~2020-07-16  5:12 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-16  5:11 [PATCH v3 0/7] arm64: perf: Proper cap_user_time* support Leo Yan
2020-07-16  5:11 ` Leo Yan
2020-07-16  5:11 ` [PATCH v3 1/7] sched_clock: Expose struct clock_read_data Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-16  5:11 ` Leo Yan [this message]
2020-07-16  5:11   ` [PATCH v3 2/7] time/sched_clock: Use raw_read_seqcount_latch() Leo Yan
2020-07-16  5:11 ` [PATCH v3 3/7] arm64: perf: Implement correct cap_user_time Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-16  5:11 ` [PATCH v3 4/7] arm64: perf: Only advertise cap_user_time for arch_timer Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-16  5:11 ` [PATCH v3 5/7] perf: Add perf_event_mmap_page::cap_user_time_short ABI Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-16  5:11 ` [PATCH v3 6/7] arm64: perf: Add cap_user_time_short Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-16  5:11 ` [PATCH v3 7/7] tools headers UAPI: Update tools's copy of linux/perf_event.h Leo Yan
2020-07-16  5:11   ` Leo Yan
2020-07-20 11:56 ` [PATCH v3 0/7] arm64: perf: Proper cap_user_time* support Will Deacon
2020-07-20 11:56   ` Will Deacon

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