linux-kernel - Re: [PATCH] mm: check for sleepable context in kvfree

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Message-ID: <3622a5fe9f13ddfd15b262dbeda700a26c395c2a.camel@kernel.org>
Date:   Tue, 23 Jul 2019 13:52:36 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, lhenriques@...e.com, cmaiolino@...hat.com,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] mm: check for sleepable context in kvfree

On Tue, 2019-07-23 at 09:12 -0400, Jeff Layton wrote:
> A lot of callers of kvfree only go down the vfree path under very rare
> circumstances, and so may never end up hitting the might_sleep_if in it.
> Ensure that when kvfree is called, that it is operating in a context
> where it is allowed to sleep.
> 
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Luis Henriques <lhenriques@...e.com>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  mm/util.c | 2 ++
>  1 file changed, 2 insertions(+)
> 

FWIW, I started looking at this after Luis sent me some ceph patches
that fixed a few of these problems. I have not done extensive testing
with this patch, so maybe consider this an RFC for now.

HCH points out that xfs uses kvfree as a generic "free this no matter
what it is" sort of wrapper and expects the callers to work out whether
they might be freeing a vmalloc'ed address. If that sort of usage turns
out to be prevalent, then we may need another approach to clean this up.

> diff --git a/mm/util.c b/mm/util.c
> index e6351a80f248..81ec2a003c86 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -482,6 +482,8 @@ EXPORT_SYMBOL(kvmalloc_node);
>   */
>  void kvfree(const void *addr)
>  {
> +	might_sleep_if(!in_interrupt());
> +
>  	if (is_vmalloc_addr(addr))
>  		vfree(addr);
>  	else

-- 
Jeff Layton <jlayton@...nel.org>