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/select/pselect.c | 1 + src/select/select.c | 1 + 2 files changed, 2 insertions(+) (limited to 'src/select') diff --git a/src/select/pselect.c b/src/select/pselect.c index 63ea0695..155a6eb0 100644 --- a/src/select/pselect.c +++ b/src/select/pselect.c @@ -10,6 +10,7 @@ int pselect(int n, fd_set *rfds, fd_set *wfds, fd_set *efds, const struct timesp if (ts) ts_tmp = *ts; CANCELPT_BEGIN; r = syscall(SYS_pselect6, n, rfds, wfds, efds, ts ? &ts_tmp : 0, data); + CANCELPT_TRY; CANCELPT_END; return r; } diff --git a/src/select/select.c b/src/select/select.c index 12322718..b38e7fd2 100644 --- a/src/select/select.c +++ b/src/select/select.c @@ -7,6 +7,7 @@ int select(int n, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeval *tv) int r; CANCELPT_BEGIN; r = syscall(SYS_select, n, rfds, wfds, efds, tv); + CANCELPT_TRY; CANCELPT_END; return r; } -- cgit v1.2.1