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authorTejun Heo <tj@kernel.org>2011-03-23 10:37:01 +0100
committerTejun Heo <tj@kernel.org>2011-03-23 10:37:01 +0100
commit244056f9dbbc6dc4126a301c745fa3dd67d8af3c (patch)
treedced7105f53b5d5ed34e170d77f5c6ab0172542a /kernel
parentceb6bd67f9b9db765e1c29405f26e8460391badd (diff)
job control: Don't send duplicate job control stop notification while ptraced
Just as group_exit_code shouldn't be generated when a PTRACE_CONT'd task re-enters job control stop, notifiction for the event should be suppressed too. The logic is the same as the group_exit_code generation suppression in do_signal_stop(), if SIGNAL_STOP_STOPPED is already set, the task is re-entering job control stop without intervening SIGCONT and the notifications should be suppressed. Test case follows. #include <stdio.h> #include <unistd.h> #include <signal.h> #include <time.h> #include <sys/ptrace.h> #include <sys/wait.h> static const struct timespec ts100ms = { .tv_nsec = 100000000 }; static pid_t tracee, tracer; static const char *pid_who(pid_t pid) { return pid == tracee ? "tracee" : (pid == tracer ? "tracer" : "mommy "); } static void sigchld_sigaction(int signo, siginfo_t *si, void *ucxt) { printf("%s: SIG status=%02d code=%02d (%s)\n", pid_who(getpid()), si->si_status, si->si_code, pid_who(si->si_pid)); } int main(void) { const struct sigaction chld_sa = { .sa_sigaction = sigchld_sigaction, .sa_flags = SA_SIGINFO|SA_RESTART }; siginfo_t si; sigaction(SIGCHLD, &chld_sa, NULL); tracee = fork(); if (!tracee) { tracee = getpid(); while (1) pause(); } kill(tracee, SIGSTOP); waitid(P_PID, tracee, &si, WSTOPPED); tracer = fork(); if (!tracer) { tracer = getpid(); ptrace(PTRACE_ATTACH, tracee, NULL, NULL); waitid(P_PID, tracee, &si, WSTOPPED); ptrace(PTRACE_CONT, tracee, NULL, (void *)(long)si.si_status); waitid(P_PID, tracee, &si, WSTOPPED); ptrace(PTRACE_CONT, tracee, NULL, (void *)(long)si.si_status); waitid(P_PID, tracee, &si, WSTOPPED); printf("tracer: detaching\n"); ptrace(PTRACE_DETACH, tracee, NULL, NULL); return 0; } while (1) pause(); return 0; } Before the patch, the parent gets the second notification for the tracee after the tracer detaches. si_status is zero because group_exit_code is not set by the group stop completion which triggered this notification. mommy : SIG status=19 code=05 (tracee) tracer: SIG status=00 code=05 (tracee) tracer: SIG status=19 code=04 (tracee) tracer: SIG status=00 code=05 (tracee) tracer: detaching mommy : SIG status=00 code=05 (tracee) mommy : SIG status=00 code=01 (tracer) ^C After the patch, the duplicate notification is gone. mommy : SIG status=19 code=05 (tracee) tracer: SIG status=00 code=05 (tracee) tracer: SIG status=19 code=04 (tracee) tracer: SIG status=00 code=05 (tracee) tracer: detaching mommy : SIG status=00 code=01 (tracer) ^C Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Oleg Nesterov <oleg@redhat.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/signal.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index f65403da410..f799a054f29 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -268,6 +268,10 @@ void task_clear_group_stop_pending(struct task_struct *task)
*
* CONTEXT:
* Must be called with @task->sighand->siglock held.
+ *
+ * RETURNS:
+ * %true if group stop completion should be notified to the parent, %false
+ * otherwise.
*/
static bool task_participate_group_stop(struct task_struct *task)
{
@@ -284,7 +288,11 @@ static bool task_participate_group_stop(struct task_struct *task)
if (!WARN_ON_ONCE(sig->group_stop_count == 0))
sig->group_stop_count--;
- if (!sig->group_stop_count) {
+ /*
+ * Tell the caller to notify completion iff we are entering into a
+ * fresh group stop. Read comment in do_signal_stop() for details.
+ */
+ if (!sig->group_stop_count && !(sig->flags & SIGNAL_STOP_STOPPED)) {
sig->flags = SIGNAL_STOP_STOPPED;
return true;
}