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Date: Thu, 23 Nov 2017 15:44:04 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> Cc: mhocko@...nel.org, david@...morbit.com, jack@...e.cz, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org Subject: Re: [PATCH v2] fs: handle shrinker registration failure in sget_userns On Fri, Nov 24, 2017 at 12:35:29AM +0900, Tetsuo Handa wrote: > Al Viro wrote: > > On Fri, Nov 24, 2017 at 12:04:23AM +0900, Tetsuo Handa wrote: > > > Al Viro wrote: > > > > On Thu, Nov 23, 2017 at 03:35:37PM +0100, Michal Hocko wrote: > > > > > Hopefully less screwed version. But as I've said I am not really > > > > > familiar with the code and do not feel competent to change it so please > > > > > be very careful here. I've moved the shrinker registration to > > > > > alloc_super which turned out to be simpler. > > > > > > > > I don't get it. Why the hell do we need all that PITA in the first place? > > > > Just make sget_userns() end with > > > > if (unlikely(regsiter_shrinker(&s->s_shrink) != 0)) { > > > > deactivate_locked_super(s); > > > > s = ERR_PTR(-ENOMEM); > > > > } > > > > return s; > > > > and be done with that. All there is to it... > > > > > > > > > > Doesn't deactivate_locked_super() call unregister_shrinker() ? > > > > And? unregister_shrinker() will do list_del() on empty list_head > > and kfree(NULL); where's the problem with that? > > > The problem is that calling unregister_shrinker() without successful > register_shrinker() causes crash due to s_shrink.list.{prev,next} == NULL. *shrug* shrinker->nr_deferred = kzalloc(size, GFP_KERNEL); if (!shrinker->nr_deferred) { /* make sure it's in consistent state */ INIT_LIST_HEAD(&shrinker->list); return -ENOMEM; }
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