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seqlock: use atomic writes for the sequence 

There is a data race if the sequence is written concurrently to the
read.  In C11 this has undefined behavior.  Use atomic_set; the
read side is already using atomic_read.

Reported-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20160930213106.20186-6-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-09-30 22:30:56 +01:00
parent 550276ae0a
commit f96a8cc3c6
1 changed files with 2 additions and 2 deletions
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4
include/qemu/seqlock.h
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@ -31,7 +31,7 @@ static inline void seqlock_init(QemuSeqLock *sl)
/* Lock out other writers and update the count. */
static inline void seqlock_write_begin(QemuSeqLock *sl)
{
++sl->sequence;
atomic_set(&sl->sequence, sl->sequence + 1);
/* Write sequence before updating other fields. */
smp_wmb();
@ -42,7 +42,7 @@ static inline void seqlock_write_end(QemuSeqLock *sl)
/* Write other fields before finalizing sequence. */
smp_wmb();
++sl->sequence;
atomic_set(&sl->sequence, sl->sequence + 1);
}
static inline unsigned seqlock_read_begin(QemuSeqLock *sl)