Re: [PATCH 2/4] ceph: fix buffer free while holding i_ceph_lock in __ceph_setxattr()

[Jeff Layton <jlayton@kernel.org>]

On Sat, 2019-07-20 at 00:30 +0100, Al Viro wrote:
> On Sat, Jul 20, 2019 at 12:23:08AM +0100, Al Viro wrote:
> > On Fri, Jul 19, 2019 at 07:07:49PM -0400, Jeff Layton wrote:
> > 
> > > Al pointed out on IRC that vfree should be callable under spinlock.
> > 
> > Al had been near-terminally low on caffeine at the time, posted
> > a retraction a few minutes later and went to grab some coffee...
> > 
> > > It
> > > only sleeps if !in_interrupt(), and I think that should return true if
> > > we're holding a spinlock.
> > 
> > It can be used from RCU callbacks and all such; it *can't* be used from
> > under spinlock - on non-preempt builds there's no way to recognize that.
> 
> 	Re original patch: looks like the sane way to handle that.
> Alternatively, we could add kvfree_atomic() for use in such situations,
> but I rather doubt that it's a good idea - not unless you need to free
> something under a spinlock held over a large area, which is generally
> a bad idea to start with...
> 
> 	Note that vfree_atomic() has only one caller in the entire tree,
> BTW.

In that case, I wonder if we ought to add this to the top of kvfree():

	might_sleep_if(!in_interrupt());

Might there be other places that are calling it under spinlock that are
almost always going down the kfree() path?
-- 
Jeff Layton <jlayton@kernel.org>