On Wed, Nov 13, 2024 at 5:17 PM Jan Kara <jack@xxxxxxx> wrote: > > 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> > thanks > > 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. > There is a bunch of lock round trips in this routine alone, including on i_lock itself, but that aside: I *suspect* something like spin_wait_unlocked(&inode->i_state) shipping with a full fence at the beginning of the routine would correctly allow to check all the possible waiter et al flags without acquiring the lock anymore, shaving off at least 2 lock trips in the common case. However, I don't see such a routine as is and I'm definitely not going to flame about adding it for the time being. > 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 -- Mateusz Guzik <mjguzik gmail.com>
