Re: [PATCH v2] nptl: Handle spurious EINTR when thread cancellation is disabled (BZ#29029)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 19/04/2022 09:18, Adhemerval Zanella wrote:
> 
> 
> On 19/04/2022 07:44, Szabolcs Nagy wrote:
>> The 04/14/2022 12:49, Adhemerval Zanella via Libc-alpha wrote:
>>> Some Linux interfaces never restart after being interrupted by a signal
>>> handler, regardless of the use of SA_RESTART [1].  It means that for
>>> pthread cancellation, if the target thread disables cancellation with
>>> pthread_setcancelstate and calls such interfaces (like poll or select),
>>> it should not see spurious EINTR failures due the internal SIGCANCEL.
>>>
>>> However recent changes made pthread_cancel to always sent the internal
>>> signal, regardless of the target thread cancellation status or type.
>>> To fix it, the previous semantic is restored, where the cancel signal
>>> is only sent if the target thread has cancelation enabled in
>>> asynchronous mode.
>>>
>>> The cancel state and cancel type is moved back to cancelhandling
>>> and atomic operation are used to synchronize between threads.  The
>>> patch essentially revert the following commits:
>>>
>>>   8c1c0aae20 nptl: Move cancel type out of cancelhandling
>>>   2b51742531 nptl: Move cancel state out of cancelhandling
>>>   26cfbb7162 nptl: Remove CANCELING_BITMASK
>>>
>>> However I changed the atomic operation to follow the internal C11
>>> semantic and removed the MACRO usage, it simplifies a bit the
>>> resulting code (and removes another usage of the old atomic macros).
>>>
>>> Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
>>> and powerpc64-linux-gnu.
>>>
>>> [1] https://man7.org/linux/man-pages/man7/signal.7.html
>>>
>>> Reviewed-by: Florian Weimer <fweimer@redhat.com>
>>> Tested-by: Aurelien Jarno <aurelien@aurel32.net>
>>> ---
>>> v2: Fixed some typos and extended pthread_cancel comments.
>>
>>
>> since this commit various cancel tests fail for me (unreliably)
>> on aarch64 e.g. failures from 2 different test runs:
>>
>> FAIL: nptl/tst-cancel17
>> FAIL: nptl/tst-cancelx5
>> FAIL: nptl/tst-cond7
>> FAIL: nptl/tst-pthread-raise-blocked-self
>> FAIL: nptl/tst-pthread_cancel-select-loop
>>
>> FAIL: nptl/tst-cancelx20
>> FAIL: nptl/tst-cond7
>> FAIL: nptl/tst-cond8
>> FAIL: nptl/tst-join12
>> FAIL: nptl/tst-key3
>> FAIL: nptl/tst-pthread_cancel-select-loop
>>
>> an example run of nptl/tst-cond7
>>
>> $ elf/ld.so --library-path . nptl/tst-cond7 --direct
>> round 0
>> child created
>> parent: joining now
>> round 1
>> child created
>> parent: joining now
>> round 2
>> child created
>> parent: joining now
>> round 3
>> child created
>> parent: joining now
>> round 4
>> child created
>> parent: joining now
>>
>> where it is blocked forever: it seems pthread_cancel returns without
>> sending a signal (__pthread_kill_internal is not called) so join hangs.
>>
> 
> But the signal should be only sent if thread is is cancelled and has
> async cancellation enabled, which is not the case for the tests. 

Scratch that, I keep forgetting about __pthread_enable_asynccancel....