From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, edumazet@google.com,
eric.dumazet@gmail.com, bp@alien8.de, peterz@infradead.org
Subject: [PATCH 2/2] x86/percpu: Fix this_cpu_read()
Date: Thu, 11 Oct 2018 12:38:27 +0200 [thread overview]
Message-ID: <20181011104019.748208519@infradead.org> (raw)
In-Reply-To: 20181011103825.023036082@infradead.org
Eric reported that a sequence count loop using this_cpu_read() got
optimized out. This is wrong, this_cpu_read() must imply READ_ONCE()
because the interface is IRQ-safe, therefore an interrupt can have
changed the per-cpu value.
Fixes: 59eaef78bfea ("x86/tsc: Remodel cyc2ns to use seqcount_latch()")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/percpu.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -185,22 +185,22 @@ do { \
typeof(var) pfo_ret__; \
switch (sizeof(var)) { \
case 1: \
- asm(op "b "__percpu_arg(1)",%0" \
+ asm volatile(op "b "__percpu_arg(1)",%0"\
: "=q" (pfo_ret__) \
: "m" (var)); \
break; \
case 2: \
- asm(op "w "__percpu_arg(1)",%0" \
+ asm volatile(op "w "__percpu_arg(1)",%0"\
: "=r" (pfo_ret__) \
: "m" (var)); \
break; \
case 4: \
- asm(op "l "__percpu_arg(1)",%0" \
+ asm volatile(op "l "__percpu_arg(1)",%0"\
: "=r" (pfo_ret__) \
: "m" (var)); \
break; \
case 8: \
- asm(op "q "__percpu_arg(1)",%0" \
+ asm volatile(op "q "__percpu_arg(1)",%0"\
: "=r" (pfo_ret__) \
: "m" (var)); \
break; \
next prev parent reply other threads:[~2018-10-11 10:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-11 10:38 [PATCH 0/2] x86/tsc: Fix native_sched_clock() Peter Zijlstra
2018-10-11 10:38 ` [PATCH 1/2] x86/tsc: Force inlining of cyc2ns bits Peter Zijlstra
2018-10-14 9:15 ` [tip:x86/urgent] " tip-bot for Peter Zijlstra
2018-10-11 10:38 ` Peter Zijlstra [this message]
2018-10-11 15:02 ` [PATCH 2/2] x86/percpu: Fix this_cpu_read() Eric Dumazet
2018-10-11 15:24 ` Eric Dumazet
2018-10-11 15:50 ` Peter Zijlstra
2018-10-11 16:08 ` Eric Dumazet
2018-10-14 9:16 ` [tip:x86/urgent] " tip-bot for Peter Zijlstra
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