LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Darren Hart <dvhart@infradead.org>,
	linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] futex: Don't enable IRQs unconditionally in put_pi_state()
Date: Mon, 9 Nov 2020 12:21:28 +0100
Message-ID: <20201109112128.GF2594@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201106085205.GA1159983@mwanda>

On Fri, Nov 06, 2020 at 11:52:05AM +0300, Dan Carpenter wrote:
> The exit_pi_state_list() function calls put_pi_state() with IRQs
> disabled and is not expecting that IRQs will be enabled inside the
> function.  Use the _irqsave() so that IRQs are restored to the original
> state instead of enabled unconditionally.
> 
> Fixes: 153fbd1226fb ("futex: Fix more put_pi_state() vs. exit_pi_state_list() races")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is from static analysis and not tested.  I am not very familiar
> with futex code.

It it exceedingly rare if at all possible to trigger this, but yes, your
patch is correct.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> 
>  kernel/futex.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index f8614ef4ff31..ca84745713bc 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -788,8 +788,9 @@ static void put_pi_state(struct futex_pi_state *pi_state)
>  	 */
>  	if (pi_state->owner) {
>  		struct task_struct *owner;
> +		unsigned long flags;
>  
> -		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
> +		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
>  		owner = pi_state->owner;
>  		if (owner) {
>  			raw_spin_lock(&owner->pi_lock);
> @@ -797,7 +798,7 @@ static void put_pi_state(struct futex_pi_state *pi_state)
>  			raw_spin_unlock(&owner->pi_lock);
>  		}
>  		rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
> -		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
> +		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
>  	}
>  
>  	if (current->pi_state_cache) {
> -- 
> 2.28.0
> 

  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-06  8:52 Dan Carpenter
2020-11-09 11:21 ` Peter Zijlstra [this message]
2020-11-09 13:34 ` [tip: locking/urgent] " tip-bot2 for Dan Carpenter

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201109112128.GF2594@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=dan.carpenter@oracle.com \
    --cc=dvhart@infradead.org \
    --cc=kernel-janitors@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git