From 7cc9496a18c3fa665c286b8be41d790c795e0171 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 6 Jul 2020 17:56:19 -0400 Subject: [PATCH] make thread killlock async-signal-safe for pthread_kill pthread_kill is required to be AS-safe. that requirement can't be met if the target thread's killlock can be taken in contexts where application-installed signal handlers can run. block signals around use of this lock in all pthread_* functions which target a tid, and reorder blocking/unblocking of signals in pthread_exit so that they're blocked whenever the killlock is held. --- src/thread/pthread_create.c | 11 ++++++----- src/thread/pthread_getschedparam.c | 3 +++ src/thread/pthread_kill.c | 3 +++ src/thread/pthread_setschedparam.c | 3 +++ src/thread/pthread_setschedprio.c | 3 +++ 5 files changed, 18 insertions(+), 5 deletions(-) diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index 6bdfb44f..10f1b7d8 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -72,12 +72,13 @@ _Noreturn void __pthread_exit(void *result) /* Access to target the exiting thread with syscalls that use * its kernel tid is controlled by killlock. For detached threads, * any use past this point would have undefined behavior, but for - * joinable threads it's a valid usage that must be handled. */ + * joinable threads it's a valid usage that must be handled. + * Signals must be blocked since pthread_kill must be AS-safe. */ + __block_app_sigs(&set); LOCK(self->killlock); - /* The thread list lock must be AS-safe, and thus requires - * application signals to be blocked before it can be taken. */ - __block_app_sigs(&set); + /* The thread list lock must be AS-safe, and thus depends on + * application signals being blocked above. */ __tl_lock(); /* If this is the only thread in the list, don't proceed with @@ -85,8 +86,8 @@ _Noreturn void __pthread_exit(void *result) * signal state to prepare for exit to call atexit handlers. */ if (self->next == self) { __tl_unlock(); - __restore_sigs(&set); UNLOCK(self->killlock); + __restore_sigs(&set); exit(0); } diff --git a/src/thread/pthread_getschedparam.c b/src/thread/pthread_getschedparam.c index 1cba073d..c098befb 100644 --- a/src/thread/pthread_getschedparam.c +++ b/src/thread/pthread_getschedparam.c @@ -4,6 +4,8 @@ int pthread_getschedparam(pthread_t t, int *restrict policy, struct sched_param *restrict param) { int r; + sigset_t set; + __block_app_sigs(&set); LOCK(t->killlock); if (!t->tid) { r = ESRCH; @@ -14,5 +16,6 @@ int pthread_getschedparam(pthread_t t, int *restrict policy, struct sched_param } } UNLOCK(t->killlock); + __restore_sigs(&set); return r; } diff --git a/src/thread/pthread_kill.c b/src/thread/pthread_kill.c index 3d9395cb..446254b6 100644 --- a/src/thread/pthread_kill.c +++ b/src/thread/pthread_kill.c @@ -4,9 +4,12 @@ int pthread_kill(pthread_t t, int sig) { int r; + sigset_t set; + __block_app_sigs(&set); LOCK(t->killlock); r = t->tid ? -__syscall(SYS_tkill, t->tid, sig) : (sig+0U >= _NSIG ? EINVAL : 0); UNLOCK(t->killlock); + __restore_sigs(&set); return r; } diff --git a/src/thread/pthread_setschedparam.c b/src/thread/pthread_setschedparam.c index 038d13d8..76d4d45a 100644 --- a/src/thread/pthread_setschedparam.c +++ b/src/thread/pthread_setschedparam.c @@ -4,8 +4,11 @@ int pthread_setschedparam(pthread_t t, int policy, const struct sched_param *param) { int r; + sigset_t set; + __block_app_sigs(&set); LOCK(t->killlock); r = !t->tid ? ESRCH : -__syscall(SYS_sched_setscheduler, t->tid, policy, param); UNLOCK(t->killlock); + __restore_sigs(&set); return r; } diff --git a/src/thread/pthread_setschedprio.c b/src/thread/pthread_setschedprio.c index 5bf4a019..fc2e13dd 100644 --- a/src/thread/pthread_setschedprio.c +++ b/src/thread/pthread_setschedprio.c @@ -4,8 +4,11 @@ int pthread_setschedprio(pthread_t t, int prio) { int r; + sigset_t set; + __block_app_sigs(&set); LOCK(t->killlock); r = !t->tid ? ESRCH : -__syscall(SYS_sched_setparam, t->tid, &prio); UNLOCK(t->killlock); + __restore_sigs(&set); return r; } -- 2.21.0