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posix: Fix system blocks SIGCHLD erroneously [BZ #30163]

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Fix bug that SIGCHLD is erroneously blocked forever in the following
scenario:

1. Thread A calls system but hasn't returned yet
2. Thread B calls another system but returns

SIGCHLD would be blocked forever in thread B after its system() returns,
even after the system() in thread A returns.

Although POSIX does not require, glibc system implementation aims to be
thread and cancellation safe. This bug was introduced in
5fb7fc9635 when we moved reverting signal
mask to happen when the last concurrently running system returns,
despite that signal mask is per thread. This commit reverts this logic
and adds a test.

Signed-off-by: Adam Yi <ayi@janestreet.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Adam Yi
2023-03-07 07:30:02 -05:00
committed by Adhemerval Zanella
parent 969e9733c7
commit 436a604b7d
7 changed files with 140 additions and 3 deletions
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6
sysdeps/posix/system.c
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@@ -179,16 +179,16 @@ do_system (const char *line)
as if the shell had terminated using _exit(127). */
status = W_EXITCODE (127, 0);
/* sigaction can not fail with SIGINT/SIGQUIT used with old
disposition. Same applies for sigprocmask. */
DO_LOCK ();
if (SUB_REF () == 0)
{
/* sigaction can not fail with SIGINT/SIGQUIT used with old
disposition. Same applies for sigprocmask. */
__sigaction (SIGINT, &intr, NULL);
__sigaction (SIGQUIT, &quit, NULL);
__sigprocmask (SIG_SETMASK, &omask, NULL);
}
DO_UNLOCK ();
__sigprocmask (SIG_SETMASK, &omask, NULL);
if (ret != 0)
__set_errno (ret);