From 52ee0dd6d5ccefcbf9b55748896c85801bfafd17 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 6 Jul 2020 18:46:57 -0400 Subject: fix async-cancel-safety of pthread_cancel 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. --- src/thread/pthread_kill.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/src/thread/pthread_kill.c b/src/thread/pthread_kill.c index 446254b6..79ddb209 100644 --- a/src/thread/pthread_kill.c +++ b/src/thread/pthread_kill.c @@ -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); -- cgit v1.2.1