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authorOleg Nesterov <oleg@redhat.com>2014-04-07 15:38:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-07 16:36:06 -0700
commit7c733eb3eac0e3d091aaf37c183d2175eeebfb2b (patch)
tree34616ad33e80a2a422a73febc28195abfe5f2b48 /kernel/exit.c
parent377d75dafa07ee0da64223c9169f4e17b26c2b9a (diff)
downloadlinux-sh-7c733eb3eac0e3d091aaf37c183d2175eeebfb2b.tar.gz
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@redhat.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Jan Kratochvil <jan.kratochvil@redhat.com> Cc: Lennart Poettering <lpoetter@redhat.com> Cc: Michal Schmidt <mschmidt@redhat.com> Cc: Roland McGrath <roland@hack.frob.com> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/exit.c')
-rw-r--r--kernel/exit.c22
1 files changed, 9 insertions, 13 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 92d38d4da4b1..6ed6a1d552b5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1380,20 +1380,16 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
/* 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