From b470030f839a375e5030ec9d44903ef7581c15a2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Thu, 24 Mar 2011 14:18:00 -0400 Subject: overhaul cancellation to fix resource leaks and dangerous behavior with signals this commit addresses two issues: 1. a race condition, whereby a cancellation request occurring after a syscall returned from kernelspace but before the subsequent CANCELPT_END would cause cancellable resource-allocating syscalls (like open) to leak resources. 2. signal handlers invoked while the thread was blocked at a cancellation point behaved as if asynchronous cancellation mode wer in effect, resulting in potentially dangerous state corruption if a cancellation request occurs. the glibc/nptl implementation of threads shares both of these issues. with this commit, both are fixed. however, cancellation points encountered in a signal handler will not be acted upon if the signal was received while the thread was already at a cancellation point. they will of course be acted upon after the signal handler returns, so in real-world usage where signal handlers quickly return, it should not be a problem. it's possible to solve this problem too by having sigaction() wrap all signal handlers with a function that uses a pthread_cleanup handler to catch cancellation, patch up the saved context, and return into the cancellable function that will catch and act upon the cancellation. however that would be a lot of complexity for minimal if any benefit... --- src/thread/pthread_cond_timedwait.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'src/thread/pthread_cond_timedwait.c') diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c index 228f61f7..1439aace 100644 --- a/src/thread/pthread_cond_timedwait.c +++ b/src/thread/pthread_cond_timedwait.c @@ -8,19 +8,21 @@ static void relock(void *m) int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct timespec *ts) { int r, e=0; - CANCELPT(0); + CANCELPT_BEGIN; + CANCELPT_END; pthread_cleanup_push(relock, m); c->_c_block = 1; if ((r=pthread_mutex_unlock(m))) return r; - CANCELPT(1); + CANCELPT_BEGIN; e = __timedwait(&c->_c_block, 1, c->_c_clock, ts, 0); - CANCELPT(0); + CANCELPT_END; pthread_cleanup_pop(0); if ((r=pthread_mutex_lock(m))) return r; - CANCELPT(0); + CANCELPT_BEGIN; + CANCELPT_END; return e; } -- cgit v1.2.1