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/internal/libc.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'src/internal') diff --git a/src/internal/libc.h b/src/internal/libc.h index 3d09bf6a..bbbb3a4c 100644 --- a/src/internal/libc.h +++ b/src/internal/libc.h @@ -44,7 +44,8 @@ void __lockfile(FILE *); #define UNLOCK(x) (*(x)=0) #define CANCELPT(x) (libc.cancelpt ? libc.cancelpt((x)),0 : (void)(x),0) #define CANCELPT_BEGIN CANCELPT(1) -#define CANCELPT_END CANCELPT(0) +#define CANCELPT_TRY CANCELPT(0) +#define CANCELPT_END CANCELPT(-1) extern char **__environ; #define environ __environ -- cgit v1.2.1