[Devel] [PATCH 0/2] fuse: fix signals handling while processing request

[Stanislav Kinsburskiy]

14.10.2016 02:23, Maxim Patlasov пишет:
> Stas,
>
>
> The series look fine, so:
>
> Acked-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
>
>
> But, please, refine the description of the second patch. It must 
> explain clearly why the patch fixes the problem:
>
> block_sigs() blocks ordinary non-fatal signals as expected, but 
> surprisingly SIGTRAP is special: it does not matter whether it comes 
> before or after block_sigs(), the latter does not affect SIGTRAP at 
> all! And in contrast, wait_event_killable() is immune to it -- only 
> fatal sig can wake it up.
>

No, Maxim. You make a mistake here.
There is nothing special with SIGTRAP (although it's being sometimes 
sent via force_sig_info()).
The problem is described as it is: block_sigs() doesn't (!) clear 
TIG_SIGPENDING flag. All it does is blocking future signals to arrive.
Moreover, __set_task_blocked() call recalc_sigpending(), which check 
whether any of the signals to block is present in process pending mask, 
and if so - set (!) TIF_SIGPENDING on the task.
IOW, any pending signal remains pending after call to blocks_sigs().
And that's is the root of the issue (as it described in the patch comment).

> Thanks,
> Maxim
>
> On 10/13/2016 03:03 AM, Stanislav Kinsburskiy wrote:
>> This patch fixes wrong SIGBUS result in page fault handler for fuse 
>> file, when
>> process received a signal.
>>
>> https://jira.sw.ru/browse/PSBM-53581
>>
>> ---
>>
>> Stanislav Kinsburskiy (2):
>>        new helper: wait_event_killable_exclusive()
>>        fuse: handle only fatal signals while waiting request answer
>>
>>
>>   fs/fuse/dev.c        |   42 ++++++++++++++++--------------------------
>>   include/linux/wait.h |   26 ++++++++++++++++++++++++++
>>   2 files changed, 42 insertions(+), 26 deletions(-)
>>
>> -- 
>