On Thu, 11 Sep 2014, Dave Jones wrote:
> Hit this overnight on Linus tree from yesterday.
>
> BUG: sleeping function called from invalid context at
> include/linux/freezer.h:56
> in_atomic(): 1, irqs_disabled(): 0, pid: 31948, name: trinity-c121
> Preemption disabled at:[<ffffffffb90f2512>] futex_wait_setup+0xb2/0x140
Huch? So we are in a preempt disabled region in futex_wait_setup and
we get interrupted and end up in the signal delivery path?
I really love that futex stuff....
But fortunately the preemption disabled hint made it into mainline so
looking at the callsites of futex_wait_setup() makes it pretty clear
where the shit hits the fan. Patch below.
Thanks,
tglx
------------------->
From: Thomas Gleixner <[email protected]>
Date: Thu, 11 Sep 2014 23:44:35 +0200
Subject: futex: Unlock hb->lock in futex_wait_requeue_pi() error path
futex_wait_requeue_pi() calls futex_wait_setup(). If
futex_wait_setup() succeeds it returns with hb->lock held and
preemption disabled. Now the sanity check after this does:
if (match_futex(&q.key, &key2)) {
ret = -EINVAL;
goto out_put_keys;
}
which releases the keys but does not release hb->lock. So we happily
return to user space with hb->lock held and therefor preemption
disabled.
Unlock hb->lock before taking the exit route.
Reported-by: Dave "Trinity" Jones <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
---
diff --git a/kernel/futex.c b/kernel/futex.c
index d3a9d946d0b7..815d7af2ffe8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2592,6 +2592,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr,
unsigned int flags,
* shared futexes. We need to compare the keys:
*/
if (match_futex(&q.key, &key2)) {
+ queue_unlock(hb);
ret = -EINVAL;
goto out_put_keys;
}
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