path: root/src/process/waitpid.c
diff options
authorRich Felker <>2011-03-24 14:18:00 -0400
committerRich Felker <>2011-03-24 14:18:00 -0400
commitb470030f839a375e5030ec9d44903ef7581c15a2 (patch)
tree462b1df89a3ea45bcf50b9d0a844472576ed6585 /src/process/waitpid.c
parent095820016689dfdc9141f477a86de22054c86078 (diff)
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...
Diffstat (limited to 'src/process/waitpid.c')
1 files changed, 7 insertions, 1 deletions
diff --git a/src/process/waitpid.c b/src/process/waitpid.c
index ec2757b3..5e0320f7 100644
--- a/src/process/waitpid.c
+++ b/src/process/waitpid.c
@@ -1,7 +1,13 @@
#include <sys/wait.h>
#include "syscall.h"
+#include "libc.h"
pid_t waitpid(pid_t pid, int *status, int options)
- return syscall(SYS_wait4, pid, status, options, 0);
+ int r;
+ r = syscall(SYS_wait4, pid, status, options, 0);
+ if (r<0) CANCELPT_TRY;
+ return r;