Commit d12f7309 authored by Emilio G. Cota's avatar Emilio G. Cota Committed by Paolo Bonzini
Browse files

seqlock: read sequence number atomically 



With this change we make sure that the compiler will not
optimise the read of the sequence number in any way.

Signed-off-by: default avatarEmilio G. Cota <cota@braap.org>
Message-Id: <1440375847-17603-8-git-send-email-cota@braap.org>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 123fdbac

include/qemu/seqlock.h

+3 −3
Original line number Diff line number Diff line
@@ -55,18 +55,18 @@ static inline void seqlock_write_unlock(QemuSeqLock *sl) 
static inline unsigned seqlock_read_begin(QemuSeqLock *sl)

{

    /* Always fail if a write is in progress.  */

    unsigned ret = sl->sequence & ~1;

    unsigned ret = atomic_read(&sl->sequence);



    /* Read sequence before reading other fields.  */

    smp_rmb();

    return ret;

    return ret & ~1;

}



static inline int seqlock_read_retry(const QemuSeqLock *sl, unsigned start)

{

    /* Read other fields before reading final sequence.  */

    smp_rmb();

    return unlikely(sl->sequence != start);

    return unlikely(atomic_read(&sl->sequence) != start);

}



#endif