On Wed 16-10-19 08:23:51, Eric Sandeen wrote: > On 10/16/19 4:42 AM, Jan Kara wrote: > > On Tue 15-10-19 21:36:08, Eric Sandeen wrote: > >> On 10/15/19 2:37 AM, Jan Kara wrote: > >>> On Mon 14-10-19 16:30:24, Eric Sandeen wrote: > >>>> Anything that walks all inodes on sb->s_inodes list without rescheduling > >>>> risks softlockups. > >>>> > >>>> Previous efforts were made in 2 functions, see: > >>>> > >>>> c27d82f fs/drop_caches.c: avoid softlockups in drop_pagecache_sb() > >>>> ac05fbb inode: don't softlockup when evicting inodes > >>>> > >>>> but there hasn't been an audit of all walkers, so do that now. This > >>>> also consistently moves the cond_resched() calls to the bottom of each > >>>> loop in cases where it already exists. > >>>> > >>>> One loop remains: remove_dquot_ref(), because I'm not quite sure how > >>>> to deal with that one w/o taking the i_lock. > >>>> > >>>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> > >>> > >>> Thanks Eric. The patch looks good to me. You can add: > >>> > >>> Reviewed-by: Jan Kara <jack@xxxxxxx> > >> > >> thanks > >> > >>> BTW, I suppose you need to add Al to pickup the patch? > >> > >> Yeah (cc'd now) > >> > >> But it was just pointed out to me that if/when the majority of inodes > >> at umount time have i_count == 0, we'll never hit the resched in > >> fsnotify_unmount_inodes() and may still have an issue ... > > > > Yeah, that's a good point. So that loop will need some further tweaking > > (like doing iget-iput dance in need_resched() case like in some other > > places). > > Well, it's already got an iget/iput for anything with i_count > 0. But > as the comment says (and I think it's right...) doing an iget/iput > on i_count == 0 inodes at this point would be without SB_ACTIVE and the final > iput here would actually start evicting inodes in /this/ loop, right? Yes, it would but since this is just before calling evict_inodes(), I have currently hard time remembering why evicting inodes like that would be an issue. > I think we could (ab)use the lru list to construct a "dispose" list for > fsnotify processing as was done in evict_inodes... > > or maybe the two should be merged, and fsnotify watches could be handled > directly in evict_inodes. But that doesn't feel quite right. Merging the two would be possible (and faster!) as well but I agree it feels a bit dirty :) Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
