The patch titled
Subject: signal: kill the obsolete SIGNAL_UNKILLABLE check in complete_signal()
has been added to the -mm tree. Its filename is
signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: signal: kill the obsolete SIGNAL_UNKILLABLE check in complete_signal()
complete_signal() checks SIGNAL_UNKILLABLE before it starts to destroy the
thread group, today this is unnecessary and even not 100% correct.
After the commit f008faff0e27 ("signals: protect init from unwanted
signals more") we rely on sig_task_ignored(), complete_signal(SIGKILL) can
only see a SIGNAL_UNKILLABLE task if we actually want to kill it. And
note that after the commit b3bfa0cba867 ("signals: protect cinit from
blocked fatal signals") we do not drop SIGKILL dequeued by /sbin/init.
And it does not look right. fatal_signal_pending() should always imply
that the whole thread group (except ->group_exit_task if it is not NULL)
is killed, this check breaks the rule.
This explains WARN_ON(!JOBCTL_STOP_PENDING) in task_participate_group_stop()
triggered by the test-case from Dmitry:
int main()
{
int pid = 1;
ptrace(PTRACE_ATTACH, pid, 0, 0);
ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_EXITKILL);
sleep(1);
return 0;
}
do_signal_stop()->signal_group_exit() returns false because
SIGNAL_GROUP_EXIT is not set, but task_set_jobctl_pending() checks
fatal_signal_pending() and does not set JOBCTL_STOP_PENDING.
The test-case above needs root and (correctly) crashes the kernel, but we
can trigger the same warning inside the container or using another
test-case:
static int init(void *arg)
{
for (;;)
pause();
}
int main(void)
{
char stack[16 * 1024];
for (;;) {
int pid = clone(init, stack + sizeof(stack)/2,
CLONE_NEWPID | SIGCHLD, NULL);
assert(pid > 0);
assert(ptrace(PTRACE_ATTACH, pid, 0, 0) == 0);
assert(waitpid(-1, NULL, WSTOPPED) == pid);
assert(ptrace(PTRACE_DETACH, pid, 0, SIGSTOP) == 0);
assert(syscall(__NR_tkill, pid, SIGKILL) == 0);
assert(pid == wait(NULL));
}
}
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/signal.c~signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal kernel/signal.c
--- a/kernel/signal.c~signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal
+++ a/kernel/signal.c
@@ -909,7 +909,7 @@ static void complete_signal(int sig, str
* then start taking the whole group down immediately.
*/
if (sig_fatal(p, sig) &&
- !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
+ !(signal->flags & SIGNAL_GROUP_EXIT) &&
!sigismember(&t->real_blocked, sig) &&
(sig == SIGKILL || !t->ptrace)) {
/*
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
mmoom-fix-potentially-killing-unrelated-process-fix.patch
mm-fix-the-racy-mm-locked_vm-change-in.patch
mm-add-the-struct-mm_struct-mm-local-into.patch
mm-oom_kill-remove-the-wrong-fatal_signal_pending-check-in-oom_kill_process.patch
mm-oom_kill-cleanup-the-kill-sharing-same-memory-loop.patch
mm-oom_kill-fix-the-wrong-task-mm-==-mm-checks-in-oom_kill_process.patch
proc-actually-make-proc_fd_permission-thread-friendly.patch
change-current_is_single_threaded-to-use-for_each_thread.patch
signals-kill-block_all_signals-and-unblock_all_signals.patch
signal-turn-dequeue_signal_lock-into-kernel_dequeue_signal.patch
signal-turn-dequeue_signal_lock-into-kernel_dequeue_signal-fix.patch
signal-introduce-kernel_signal_stop-to-fix-jffs2_garbage_collect_thread.patch
signal-remove-jffs2_garbage_collect_thread-allow_signalsigcont.patch
signal-kill-the-obsolete-signal_unkillable-check-in-complete_signal.patch
coredump-ensure-all-coredumping-tasks-have-signal_group_coredump.patch
coredump-change-zap_threads-and-zap_process-to-use-for_each_thread.patch
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