From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Jason A . Donenfeld" <Jason@zx2c4.com>,
linux-btrfs@vger.kernel.org,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
dsterba@suse.cz, David Howells <dhowells@redhat.com>,
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David Rientjes <rientjes@google.com>,
Waiman Long <longman@redhat.com>,
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Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()
Date: Wed, 17 Jun 2020 07:12:12 +0000 [thread overview]
Message-ID: <20200617071212.GJ9499@dhcp22.suse.cz> (raw)
In-Reply-To: <20200617003711.GD8681@bombadil.infradead.org>
On Tue 16-06-20 17:37:11, Matthew Wilcox wrote:
> On Wed, Jun 17, 2020 at 01:01:30AM +0200, David Sterba wrote:
> > On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote:
> > > On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:
> > > > v4:
> > > > - Break out the memzero_explicit() change as suggested by Dan Carpenter
> > > > so that it can be backported to stable.
> > > > - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for
> > > > now as there can be a bit more discussion on what is best. It will be
> > > > introduced as a separate patch later on after this one is merged.
> > >
> > > To this larger audience and last week without reply:
> > > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
> > >
> > > Are there _any_ fastpath uses of kfree or vfree?
> >
> > I'd consider kfree performance critical for cases where it is called
> > under locks. If possible the kfree is moved outside of the critical
> > section, but we have rbtrees or lists that get deleted under locks and
> > restructuring the code to do eg. splice and free it outside of the lock
> > is not always possible.
>
> Not just performance critical, but correctness critical. Since kvfree()
> may allocate from the vmalloc allocator, I really think that kvfree()
> should assert that it's !in_atomic(). Otherwise we can get into trouble
> if we end up calling vfree() and have to take the mutex.
FWIW __vfree already checks for atomic context and put the work into a
deferred context. So this should be safe. It should be used as a last
resort, though.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-06-17 7:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-16 1:57 [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() Waiman Long
2020-06-16 1:57 ` [PATCH v4 1/3] mm/slab: Use memzero_explicit() in kzfree() Waiman Long
2020-06-16 3:30 ` Eric Biggers
2020-06-16 13:05 ` Waiman Long
2020-06-16 15:46 ` David Howells
2020-06-16 6:42 ` Michal Hocko
2020-06-16 9:08 ` Dan Carpenter
2020-06-16 1:57 ` [PATCH v4 2/3] mm, treewide: Rename kzfree() to kfree_sensitive() Waiman Long
2020-06-16 14:26 ` Dan Carpenter
2020-06-16 15:05 ` Waiman Long
2020-06-16 1:57 ` [PATCH v4 3/3] btrfs: Use kfree() in btrfs_ioctl_get_subvol_info() Waiman Long
2020-06-16 14:48 ` David Sterba
2020-06-16 15:05 ` Waiman Long
2020-06-16 18:53 ` [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive() Joe Perches
2020-06-16 19:43 ` Waiman Long
2020-06-16 19:46 ` Jason A. Donenfeld
2020-06-16 20:01 ` Waiman Long
2020-06-16 21:14 ` Matthew Wilcox
2020-06-16 23:01 ` David Sterba
2020-06-17 0:37 ` Matthew Wilcox
2020-06-17 7:12 ` Michal Hocko [this message]
2020-06-17 11:08 ` Matthew Wilcox
2020-06-17 11:31 ` Michal Hocko
2020-06-17 12:23 ` Matthew Wilcox
2020-06-17 12:55 ` Michal Hocko
2020-06-17 8:03 ` Jo -l
2020-06-17 21:31 ` Denis Efremov
2020-06-17 23:12 ` Joe Perches
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