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From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: dsterba@suse.cz, Joe Perches <joe@perches.com>,
	Waiman Long <longman@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Howells <dhowells@redhat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
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Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()
Date: Wed, 17 Jun 2020 13:31:57 +0200
Message-ID: <20200617113157.GM9499@dhcp22.suse.cz> (raw)
In-Reply-To: <20200617110820.GG8681@bombadil.infradead.org>

On Wed 17-06-20 04:08:20, Matthew Wilcox wrote:
> On Wed, Jun 17, 2020 at 09:12:12AM +0200, Michal Hocko wrote:
> > On Tue 16-06-20 17:37:11, Matthew Wilcox wrote:
> > > 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.
> 
> Actually, it only checks for in_interrupt().

You are right. I have misremembered. You have made me look (thanks) ...

> If you call vfree() under
> a spinlock, you're in trouble.  in_atomic() only knows if we hold a
> spinlock for CONFIG_PREEMPT, so it's not safe to check for in_atomic()
> in __vfree().  So we need the warning in order that preempt people can
> tell those without that there is a bug here.

... Unless I am missing something in_interrupt depends on preempt_count() as
well so neither of the two is reliable without PREEMPT_COUNT configured.

-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-16  1:57 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
2020-06-17 11:08         ` Matthew Wilcox
2020-06-17 11:31           ` Michal Hocko [this message]
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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