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 [thread overview]
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
>
next prev parent reply other threads:[~2020-11-09 11:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-06 8:52 [PATCH] futex: Don't enable IRQs unconditionally in put_pi_state() Dan Carpenter
2020-11-09 11:21 ` Peter Zijlstra [this message]
2020-11-09 13:34 ` [tip: locking/urgent] " tip-bot2 for Dan Carpenter
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