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Exit trace loop if got ECHILD, not if nprocs == 0.

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Comment gives a testcase which wasn't handled correctly
by the old code.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2013-07-08 11:28:27 +02:00
parent f5730e9614
commit d2e1f42d8a
1 changed files with 15 additions and 3 deletions
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18
strace.c
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@ -1964,7 +1964,17 @@ trace(void)
{
struct rusage ru;
while (nprocs != 0) {
/* Used to be "while (nprocs != 0)", but in this testcase:
* int main() { _exit(!!fork()); }
* under strace -f, parent sometimes (rarely) manages
* to exit before we see the first stop of the child,
* and we are losing track of it:
* 19923 clone(...) = 19924
* 19923 exit_group(1) = ?
* 19923 +++ exited with 1 +++
* Waiting for ECHILD works better.
*/
while (1) {
int pid;
int wait_errno;
int status, sig;
@ -1985,9 +1995,11 @@ trace(void)
if (pid < 0) {
if (wait_errno == EINTR)
continue;
if (wait_errno == ECHILD)
/* Should not happen since nprocs > 0 */
if (nprocs == 0 && wait_errno == ECHILD)
return;
/* If nprocs > 0, ECHILD is not expected,
* treat it as any other error here:
*/
errno = wait_errno;
perror_msg_and_die("wait4(__WALL)");
}