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/process/waitid.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'src/process/waitid.c') diff --git a/src/process/waitid.c b/src/process/waitid.c index b1e5e9b1..4fa7c024 100644 --- a/src/process/waitid.c +++ b/src/process/waitid.c @@ -1,7 +1,13 @@ #include #include "syscall.h" +#include "libc.h" int waitid(idtype_t type, id_t id, siginfo_t *info, int options) { - return syscall(SYS_waitid, type, id, info, options, 0); + int r; + CANCELPT_BEGIN; + r = syscall(SYS_waitid, type, id, info, options, 0); + if (r<0) CANCELPT_TRY; + CANCELPT_END; + return r; } -- cgit v1.2.1