linux-kernel - [PATCH STABLE 4.4] futex: fix spin_lock() / spin_unlock

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Message-Id: <20210305153342.25248-1-tst@schoebel-theuer.de>
Date:   Fri,  5 Mar 2021 16:33:42 +0100
From:   Thomas Schoebel-Theuer <tst@...oebel-theuer.de>
To:     tst@...oebel-theuer.de,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lee Jones <lee.jones@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Schoebel-Theuer <tst@...d1.de>,
        Arnd Bergmann <arnd@...db.de>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH STABLE 4.4] futex: fix spin_lock() / spin_unlock_irq() imbalance

From: Thomas Schoebel-Theuer <tst@...d1.de>

The following is obviously incorrect:

static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
             struct futex_hash_bucket *hb)
{
[...]
	raw_spin_lock(&pi_state->pi_mutex.wait_lock);
[...]
	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
[...]
}

The 4.4-specific fix should probably go into the direction of
b4abf91047c.

Probably, backporting of b4abf91047c
to 4.4 LTS could be another good idea.

However, this might involve some more 4.4-specific work and
require thorough testing:

> git log --oneline v4.4..b4abf91047c -- kernel/futex.c kernel/locking/rtmutex.c | wc -l
10

So this patch is just an obvious quickfix for now.

Signed-off-by: Thomas Schoebel-Theuer <tst@...d1.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Lee Jones <lee.jones@...aro.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Fixes: 394fc498142
Fixes: 6510e4a2d04
---
 kernel/futex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 70ad21bbb1d5..4a707bc7cceb 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1406,7 +1406,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
 	if (pi_state->owner != current)
 		return -EINVAL;
 
-	raw_spin_lock(&pi_state->pi_mutex.wait_lock);
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
 
 	/*
-- 
2.26.2