Subject: + wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch added to -mm tree
To: oleg@xxxxxxxxxx,jan.kratochvil@xxxxxxxxxx,lpoetter@xxxxxxxxxx,mschmidt@xxxxxxxxxx,roland@xxxxxxxxxxxxx,tj@xxxxxxxxxx,viro@xxxxxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 26 Feb 2014 15:45:06 -0800
The patch titled
Subject: wait: WSTOPPED|WCONTINUED doesn't work if a zombie leader is traced by another process
has been added to the -mm tree. Its filename is
wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** 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: wait: WSTOPPED|WCONTINUED doesn't work if a zombie leader is traced by another process
Even if the main thread is dead the process still can stop/continue.
However, if the leader is ptraced wait_consider_task(ptrace => false)
always skips wait_task_stopped/wait_task_continued, so WSTOPPED or
WCONTINUED can never work for the natural parent in this case.
Move the "A zombie ptracee is only visible to its ptracer" check into the
"if (!delay_group_leader(p))" block. ->notask_error is cleared by the
"fall through" code below.
This depends on the previous change, wait_task_stopped/continued must be
avoided if !delay_group_leader() and the tracer is ->real_parent.
Otherwise WSTOPPED|WEXITED could wrongly report "stopped" when the child
is already dead (single-threaded or not). If it is traced by another task
then the "stopped" state is fine until the debugger detaches and reveals a
zombie state.
Stupid test-case:
void *tfunc(void *arg)
{
sleep(1); // wait for zombie leader
raise(SIGSTOP);
exit(0x13);
return NULL;
}
int run_child(void)
{
pthread_t thread;
if (!fork()) {
int tracee = getppid();
assert(ptrace(PTRACE_ATTACH, tracee, 0,0) == 0);
do
ptrace(PTRACE_CONT, tracee, 0,0);
while (wait(NULL) > 0);
return 0;
}
sleep(1); // wait for PTRACE_ATTACH
assert(pthread_create(&thread, NULL, tfunc, NULL) == 0);
pthread_exit(NULL);
}
int main(void)
{
int child, stat;
child = fork();
if (!child)
return run_child();
assert(child == waitpid(-1, &stat, WSTOPPED));
assert(stat == 0x137f);
kill(child, SIGCONT);
assert(child == waitpid(-1, &stat, WCONTINUED));
assert(stat == 0xffff);
assert(child == waitpid(-1, &stat, 0));
assert(stat == 0x1300);
return 0;
}
Without this patch it hangs in waitpid(WSTOPPED), wait_task_stopped() is
never called.
Note: this doesn't fix all problems with a zombie delay_group_leader(),
WCONTINUED | WEXITED check is not exactly right. debugger can't assume it
will be notified if another thread reaps the whole thread group.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jan Kratochvil <jan.kratochvil@xxxxxxxxxx>
Cc: Lennart Poettering <lpoetter@xxxxxxxxxx>
Cc: Michal Schmidt <mschmidt@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
diff -puN kernel/exit.c~wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process kernel/exit.c
--- a/kernel/exit.c~wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process
+++ a/kernel/exit.c
@@ -1382,20 +1382,16 @@ static int wait_consider_task(struct wai
/* slay zombie? */
if (p->exit_state == EXIT_ZOMBIE) {
- /*
- * A zombie ptracee is only visible to its ptracer.
- * Notification and reaping will be cascaded to the real
- * parent when the ptracer detaches.
- */
- if (likely(!ptrace) && unlikely(p->ptrace)) {
- /* it will become visible, clear notask_error */
- wo->notask_error = 0;
- return 0;
- }
-
/* we don't reap group leaders with subthreads */
- if (!delay_group_leader(p))
- return wait_task_zombie(wo, p);
+ if (!delay_group_leader(p)) {
+ /*
+ * A zombie ptracee is only visible to its ptracer.
+ * Notification and reaping will be cascaded to the
+ * real parent when the ptracer detaches.
+ */
+ if (unlikely(ptrace) || likely(!p->ptrace))
+ return wait_task_zombie(wo, p);
+ }
/*
* Allow access to stopped/continued state via zombie by
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
kthread-ensure-locality-of-task_struct-allocations.patch
mm-revert-thp-make-madv_hugepage-check-for-mm-def_flags.patch
mm-thp-add-vm_init_def_mask-and-prctl_thp_disable.patch
exec-kill-the-unnecessary-mm-def_flags-setting-in-load_elf_binary.patch
exitc-call-proc_exit_connector-after-exit_state-is-set.patch
wait-fix-reparent_leader-vs-exit_dead-exit_zombie-race.patch
wait-introduce-exit_trace-to-avoid-the-racy-exit_dead-exit_zombie-transition.patch
wait-use-exit_trace-only-if-thread_group_leaderzombie.patch
wait-completely-ignore-the-exit_dead-tasks.patch
wait-swap-exit_zombie-and-exit_dead-to-hide-exit_trace-from-user-space.patch
wait-wstoppedwcontinued-hangs-if-a-zombie-child-is-traced-by-real_parent.patch
wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch
linux-next.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
