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>
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@ -31,7 +31,7 @@ static inline void seqlock_init(QemuSeqLock *sl)
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/* Lock out other writers and update the count. */
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/* Lock out other writers and update the count. */
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static inline void seqlock_write_begin(QemuSeqLock *sl)
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static inline void seqlock_write_begin(QemuSeqLock *sl)
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{
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{
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++sl->sequence;
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atomic_set(&sl->sequence, sl->sequence + 1);
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/* Write sequence before updating other fields. */
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/* Write sequence before updating other fields. */
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smp_wmb();
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smp_wmb();
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@ -42,7 +42,7 @@ static inline void seqlock_write_end(QemuSeqLock *sl)
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/* Write other fields before finalizing sequence. */
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/* Write other fields before finalizing sequence. */
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smp_wmb();
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smp_wmb();
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++sl->sequence;
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atomic_set(&sl->sequence, sl->sequence + 1);
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}
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}
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static inline unsigned seqlock_read_begin(QemuSeqLock *sl)
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static inline unsigned seqlock_read_begin(QemuSeqLock *sl)
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