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mq_notify: block all (application) signals in the worker thread

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until the mq notification event arrives, it is mandatory that signals
be blocked. otherwise, a signal can be received, and its handler
executed, in a thread which does not yet exist on the abstract
machine.

after the point of the event arriving, having signals blocked is not a
conformance requirement but a QoI requirement. while the application
can unblock any signals it wants unblocked in the event handler
thread, if they did not start out blocked, it could not block them
without a race window where they are momentarily unblocked, and this
would preclude controlled delivery or other forms of acceptance
(sigwait, etc.) anywhere in the application.
This commit is contained in:
Rich Felker 2023-02-11 19:13:10 -05:00
parent 711673ee77
commit 0ab97350f0
1 changed files with 5 additions and 0 deletions
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5
src/mq/mq_notify.c
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@ -50,6 +50,7 @@ int mq_notify(mqd_t mqd, const struct sigevent *sev)
pthread_t td;
int s;
int cs;
sigset_t allmask, origmask;
if (!sev || sev->sigev_notify != SIGEV_THREAD)
return syscall(SYS_mq_notify, mqd, sev);
@ -64,11 +65,15 @@ int mq_notify(mqd_t mqd, const struct sigevent *sev)
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
sem_init(&args.sem, 0, 0);
sigfillset(&allmask);
pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
if (pthread_create(&td, &attr, start, &args)) {
__syscall(SYS_close, s);
pthread_sigmask(SIG_SETMASK, &origmask, 0);
errno = EAGAIN;
return -1;
}
pthread_sigmask(SIG_SETMASK, &origmask, 0);
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
sem_wait(&args.sem);