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/sem_timedwait.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'src/thread/sem_timedwait.c') diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c index ad3bf075..11a01700 100644 --- a/src/thread/sem_timedwait.c +++ b/src/thread/sem_timedwait.c @@ -9,15 +9,18 @@ int sem_timedwait(sem_t *sem, const struct timespec *at) if (a_fetch_add(sem->__val, -1) > 0) return 0; val = a_fetch_add(sem->__val, 1)+1; if (val==1) __wake(sem->__val, 1, 0); - CANCELPT_BEGIN; if (at && at->tv_nsec >= 1000000000UL) { errno = EINVAL; return -1; } + CANCELPT_BEGIN; if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) { errno = ETIMEDOUT; + CANCELPT_TRY; + CANCELPT_END; return -1; } + CANCELPT_TRY; CANCELPT_END; } } -- cgit v1.2.1