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Re: 3.14-rc2 XFS backtrace because irqs_disabled.

To: Dave Chinner <david@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 12 Feb 2014 09:57:53 -0600
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140212061038.GC13997@dastard>
References: <20140211172707.GA1749@xxxxxxxxxx> <20140211210841.GM13647@dastard> <52FA9ADA.9040803@xxxxxxxxxxx> <20140212004403.GA17129@xxxxxxxxxx> <20140212010941.GM18016@xxxxxxxxxxxxxxxxxx> <CA+55aFwoWT-0A_KTkXMkNqOy8hc=YmouTMBgWUD_z+8qYPphjA@xxxxxxxxxxxxxx> <20140212040358.GA25327@xxxxxxxxxx> <20140212042215.GN18016@xxxxxxxxxxxxxxxxxx> <20140212054043.GB13997@dastard> <20140212055027.GA28502@xxxxxxxxxx> <20140212061038.GC13997@dastard>
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On 2/12/14, 12:10 AM, Dave Chinner wrote:
> On Wed, Feb 12, 2014 at 12:50:27AM -0500, Dave Jones wrote:
>> On Wed, Feb 12, 2014 at 04:40:43PM +1100, Dave Chinner wrote:
>>
>>  > None of the XFS code disables interrupts in that path, not does is
>>  > call outside XFS except to dispatch IO. The stack is pretty deep at
>>  > this point and I know that the standard (non stacked) IO stack can
>>  > consume >3kb of stack space when it gets down to having to do memory
>>  > reclaim during GFP_NOIO allocation at the lowest level of SCSI
>>  > drivers. Stack overruns typically show up with symptoms like we are
>>  > seeing.
>>  > ..
>>  > 
>>  > Dave, before chasing ghosts, can you (like Eric originally asked)
>>  > turn on stack overrun detection?
>>
>> CONFIG_DEBUG_STACKOVERFLOW ? Already turned on.
> 
> That only checks stack usage when an interrupt is taken. If no
> interrupts are taken when stack usage is within 128 bytes of
> overflow, then it doesn't catch it.
> 
> I tend to use CONFIG_DEBUG_STACK_USAGE=y as it records the maximum
> stack usage of a process via canary overwrites and it records it in
> do_exit(). I also use the stack tracer to record the largest stack
> usage seen so I know exactly what code paths are approaching stack
> overruns...
> 
> Cheers,
> 
> Dave.
> 


I'm not sure if I'm off base here, but maybe this would make sense: check
for a corrupted stack in __might_sleep.  Compile tested only,
possibly inelegant, and/or completely wrong, but:


From: Eric Sandeen <sandeen@xxxxxxxxxx>

sched: Test for corrupted task_struct in __might_sleep

If a thread overruns the stack, it may corrupt the task_struct,
leading to false positives on tests like irqs_disabled().

Warn if this seems to be the case.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b46131e..6920c3c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6934,6 +6934,8 @@ static inline int preempt_count_equals(int preempt_offset)
 
 void __might_sleep(const char *file, int line, int preempt_offset)
 {
+       struct task_struct *tsk = current;
+       unsigned long *stackend;
        static unsigned long prev_jiffy;        /* ratelimiting */
 
        rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
@@ -6952,6 +6954,11 @@ void __might_sleep(const char *file, int line, int 
preempt_offset)
                        in_atomic(), irqs_disabled(),
                        current->pid, current->comm);
 
+       /* A corrupted stack can cause a false positive on irqs_disabled etc */
+       stackend = end_of_stack(tsk);
+       if (tsk != &init_task && *stackend != STACK_END_MAGIC)
+               printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
+       
        debug_show_held_locks(current);
        if (irqs_disabled())
                print_irqtrace_events(current);


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