Re: [PATCH] vfs: make evict() use smp_mb__after_spinlock instead of smp_mb

[Jan Kara]

On Wed 13-11-24 16:51:03, Mateusz Guzik wrote:
> It literally directly follows a spin_lock() call.
> 
> This whacks an explicit barrier on x86-64.
> 
> Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

> This plausibly can go away altogether, but I could not be arsed to
> convince myself that's correct. Individuals willing to put in time are
> welcome :)

AFAICS there's nothing else really guaranteeing the last store to
inode->i_state cannot be reordered up to after the wake up so I think the
barrier should be there.

								Honza
> 
>  fs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index e5a60084a7a9..b3db1234737f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -817,7 +817,7 @@ static void evict(struct inode *inode)
>  	 * ___wait_var_event() either sees the bit cleared or
>  	 * waitqueue_active() check in wake_up_var() sees the waiter.
>  	 */
> -	smp_mb();
> +	smp_mb__after_spinlock();
>  	inode_wake_up_bit(inode, __I_NEW);
>  	BUG_ON(inode->i_state != (I_FREEING | I_CLEAR));
>  	spin_unlock(&inode->i_lock);
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR