Re: [PATCH] seqlock: fix seqlock_write_unlock_impl function

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/01/20 15:49, Luc Michel wrote:
> The seqlock write unlock function was incorrectly calling
> seqlock_write_begin() instead of seqlock_write_end(), and was releasing
> the lock before incrementing the sequence. This could lead to a race
> condition and a corrupted sequence number becoming odd even though the
> lock is not held.
> 
> Signed-off-by: Luc Michel <luc.michel@greensocs.com>
> ---
>  include/qemu/seqlock.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h
> index fd408b7ec5..8b6b4ee4bb 100644
> --- a/include/qemu/seqlock.h
> +++ b/include/qemu/seqlock.h
> @@ -53,15 +53,15 @@ static inline void seqlock_write_lock_impl(QemuSeqLock *sl, QemuLockable *lock)
>      seqlock_write_begin(sl);
>  }
>  #define seqlock_write_lock(sl, lock) \
>      seqlock_write_lock_impl(sl, QEMU_MAKE_LOCKABLE(lock))
>  
> -/* Lock out other writers and update the count.  */
> +/* Update the count and release the lock.  */
>  static inline void seqlock_write_unlock_impl(QemuSeqLock *sl, QemuLockable *lock)
>  {
> +    seqlock_write_end(sl);
>      qemu_lockable_unlock(lock);
> -    seqlock_write_begin(sl);
>  }
>  #define seqlock_write_unlock(sl, lock) \
>      seqlock_write_unlock_impl(sl, QEMU_MAKE_LOCKABLE(lock))
>  
>  
> 

Queued, thanks very much.

Paolo