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From: Stephen Rothwell <sfr@canb.auug.org.au>
To: Amol Grover <frextrite@gmail.com>
Cc: James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	linux-kernel@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	Joel Fernandes <joel@joelfernandes.org>,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH RESEND] device_cgroup: Fix RCU list debugging warning
Date: Sun, 7 Jun 2020 06:23:40 +1000	[thread overview]
Message-ID: <20200607062340.7be7e8d5@canb.auug.org.au> (raw)
In-Reply-To: <20200406105950.GA2285@workstation-kernel-dev>

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Hi all,

On Mon, 6 Apr 2020 16:29:50 +0530 Amol Grover <frextrite@gmail.com> wrote:
>
> exceptions may be traversed using list_for_each_entry_rcu()
> outside of an RCU read side critical section BUT under the
> protection of decgroup_mutex. Hence add the corresponding
> lockdep expression to fix the following false-positive
> warning:
> 
> [    2.304417] =============================
> [    2.304418] WARNING: suspicious RCU usage
> [    2.304420] 5.5.4-stable #17 Tainted: G            E
> [    2.304422] -----------------------------
> [    2.304424] security/device_cgroup.c:355 RCU-list traversed in non-reader section!!
> 
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> ---
>  security/device_cgroup.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 7d0f8f7431ff..b7da9e0970d9 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -352,7 +352,8 @@ static bool match_exception_partial(struct list_head *exceptions, short type,
>  {
>  	struct dev_exception_item *ex;
>  
> -	list_for_each_entry_rcu(ex, exceptions, list) {
> +	list_for_each_entry_rcu(ex, exceptions, list,
> +				lockdep_is_held(&devcgroup_mutex)) {
>  		if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
>  			continue;
>  		if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
> -- 
> 2.24.1
> 

I have been carrying the above patch in linux-next for some time now.
I have been carrying it because it fixes problems for syzbot (see the
third warning in
https://lore.kernel.org/linux-next/CACT4Y+YnjK+kq0pfb5fe-q1bqe2T1jq_mvKHf--Z80Z3wkyK1Q@mail.gmail.com/).
Is there some reason it has not been applied to some tree?

-- 
Cheers,
Stephen Rothwell

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  reply	other threads:[~2020-06-06 20:23 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-06 10:59 Amol Grover
2020-06-06 20:23 ` Stephen Rothwell [this message]
2020-06-07 19:08   ` Paul E. McKenney
2020-06-08  4:17     ` Serge E. Hallyn
2020-08-17  2:07       ` Stephen Rothwell
2020-08-20 18:28         ` James Morris
2020-08-20 22:38           ` Stephen Rothwell

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