Re: [PATCH linux-4.1.y] sched/wait: Fix signal handling in bit wait helpers

[Florian Fainelli <f.fainelli@gmail.com>]

On 04/18/2017 06:46 AM, Oleg Nesterov wrote:
> Just curious, any particular reason you want to backport this patch?
> 
> because nobody understands why it actually helped.

While working with a customer we found this patch and it did solve the
original reporters' problem and matched the issue reported by Vladimir.

> 
> and please note that this patch is buggy, fixed by dfd01f0260
> "sched/wait: Fix the signal handling fix"

Ah, thanks, I missed that one!

Since Peter's fix is on top of this change, how should we proceed with
the stable-4.1 kernel? Alex, do you still actively maintain linux-4.1.y?

> 
> Oleg.
> 
> On 04/12, Florian Fainelli wrote:
>>
>> From: Peter Zijlstra <peterz@infradead.org>
>>
>> [ Upstream commit 68985633bccb6066bf1803e316fbc6c1f5b796d6 ]
>>
>> Vladimir reported getting RCU stall warnings and bisected it back to
>> commit:
>>
>>   743162013d40 ("sched: Remove proliferation of wait_on_bit() action functions")
>>
>> That commit inadvertently reversed the calls to schedule() and signal_pending(),
>> thereby not handling the case where the signal receives while we sleep.
>>
>> Reported-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>> Cc: Mike Galbraith <efault@gmx.de>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: mark.rutland@arm.com
>> Cc: neilb@suse.de
>> Cc: oleg@redhat.com
>> Fixes: 743162013d40 ("sched: Remove proliferation of wait_on_bit() action functions")
>> Fixes: cbbce8220949 ("SCHED: add some "wait..on_bit...timeout()" interfaces.")
>> Link: http://lkml.kernel.org/r/20151201130404.GL3816@twins.programming.kicks-ass.net
>> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>> ---
>>  kernel/sched/wait.c | 16 ++++++++--------
>>  1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
>> index 852143a79f36..e0bb7e6c4fb0 100644
>> --- a/kernel/sched/wait.c
>> +++ b/kernel/sched/wait.c
>> @@ -583,18 +583,18 @@ EXPORT_SYMBOL(wake_up_atomic_t);
>>  
>>  __sched int bit_wait(struct wait_bit_key *word)
>>  {
>> -	if (signal_pending_state(current->state, current))
>> -		return 1;
>>  	schedule();
>> +	if (signal_pending(current))
>> +		return -EINTR;
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL(bit_wait);
>>  
>>  __sched int bit_wait_io(struct wait_bit_key *word)
>>  {
>> -	if (signal_pending_state(current->state, current))
>> -		return 1;
>>  	io_schedule();
>> +	if (signal_pending(current))
>> +		return -EINTR;
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL(bit_wait_io);
>> @@ -602,11 +602,11 @@ EXPORT_SYMBOL(bit_wait_io);
>>  __sched int bit_wait_timeout(struct wait_bit_key *word)
>>  {
>>  	unsigned long now = ACCESS_ONCE(jiffies);
>> -	if (signal_pending_state(current->state, current))
>> -		return 1;
>>  	if (time_after_eq(now, word->timeout))
>>  		return -EAGAIN;
>>  	schedule_timeout(word->timeout - now);
>> +	if (signal_pending(current))
>> +		return -EINTR;
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL_GPL(bit_wait_timeout);
>> @@ -614,11 +614,11 @@ EXPORT_SYMBOL_GPL(bit_wait_timeout);
>>  __sched int bit_wait_io_timeout(struct wait_bit_key *word)
>>  {
>>  	unsigned long now = ACCESS_ONCE(jiffies);
>> -	if (signal_pending_state(current->state, current))
>> -		return 1;
>>  	if (time_after_eq(now, word->timeout))
>>  		return -EAGAIN;
>>  	io_schedule_timeout(word->timeout - now);
>> +	if (signal_pending(current))
>> +		return -EINTR;
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
>> -- 
>> 2.12.1
>>
> 


-- 
Florian