From: Thomas Schoebel-Theuer tst@1und1.de
This patch and problem analysis is specific for 4.4 LTS, due to incomplete backporting of other fixes. Later LTS series have different backports.
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 in the direction of b4abf91047c, making everything irq-safe.
Probably, backporting of b4abf91047c to 4.4 LTS could thus 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.
Hint: the lock order is documented in 4.9.y and later. A similar documenting is missing in 4.4.y. Please somebody either backport also, or write a new description, if there would be some differences I cannot easily see at the moment. Without reliable docs, inspection of the locking correctness may become a pain.
Signed-off-by: Thomas Schoebel-Theuer tst@1und1.de Cc: Thomas Gleixner tglx@linutronix.de Cc: Lee Jones lee.jones@linaro.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.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);
/*