linux-kernel - Re: [PATCH 2/4] ceph: fix buffer free while holding i_ceph_lock in __ceph

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Date:   Sat, 20 Jul 2019 00:30:32 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Luis Henriques <lhenriques@...e.com>,
        Ilya Dryomov <idryomov@...il.com>, Sage Weil <sage@...hat.com>,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] ceph: fix buffer free while holding i_ceph_lock in
 __ceph_setxattr()

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.