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

[Szabolcs Nagy]

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.