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fix async-cancel-safety of pthread_cancel

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the previous commit addressing async-signal-safety issues around
pthread_kill did not fully fix pthread_cancel, which is also required
(albeit rather irrationally) to be async-cancel-safe.

without blocking implementation-internal signals, it's possible that,
when async cancellation is enabled, a cancel signal sent by another
thread interrupts pthread_kill while the killlock for a targeted
thread is held. as a result, the calling thread will terminate due to
cancellation without ever unlocking the targeted thread's killlock,
and thus the targeted thread will be unable to exit.
This commit is contained in:
Rich Felker 2020-07-06 18:46:57 -04:00
parent 7cc9496a18
commit 52ee0dd6d5
1 changed files with 4 additions and 1 deletions
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5
src/thread/pthread_kill.c
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@ -5,7 +5,10 @@ int pthread_kill(pthread_t t, int sig)
{
int r;
sigset_t set;
__block_app_sigs(&set);
/* Block not just app signals, but internal ones too, since
* pthread_kill is used to implement pthread_cancel, which
* must be async-cancel-safe. */
__block_all_sigs(&set);
LOCK(t->killlock);
r = t->tid ? -__syscall(SYS_tkill, t->tid, sig)
: (sig+0U >= _NSIG ? EINVAL : 0);