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authorOleg Nesterov <oleg@redhat.com>2014-04-07 15:38:41 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-04-26 17:13:20 -0700
commitd66d2078181ddf2d26585c6737ea43ea8a6f52e6 (patch)
parent371d9bb7dab6293e79aafb5481b842629a60aa5e (diff)
wait: fix reparent_leader() vs EXIT_DEAD->EXIT_ZOMBIE race
commit dfccbb5e49a621c1b21a62527d61fc4305617aca upstream. wait_task_zombie() first does EXIT_ZOMBIE->EXIT_DEAD transition and drops tasklist_lock. If this task is not the natural child and it is traced, we change its state back to EXIT_ZOMBIE for ->real_parent. The last transition is racy, this is even documented in 50b8d257486a "ptrace: partially fix the do_wait(WEXITED) vs EXIT_DEAD->EXIT_ZOMBIE race". wait_consider_task() tries to detect this transition and clear ->notask_error but we can't rely on ptrace_reparented(), debugger can exit and do ptrace_unlink() before its sub-thread sets EXIT_ZOMBIE. And there is another problem which were missed before: this transition can also race with reparent_leader() which doesn't reset >exit_signal if EXIT_DEAD, assuming that this task must be reaped by someone else. So the tracee can be re-parented with ->exit_signal != SIGCHLD, and if /sbin/init doesn't use __WALL it becomes unreapable. Change reparent_leader() to update ->exit_signal even if EXIT_DEAD. Note: this is the simple temporary hack for -stable, it doesn't try to solve all problems, it will be reverted by the next changes. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reported-by: Jan Kratochvil <jan.kratochvil@redhat.com> Reported-by: Michal Schmidt <mschmidt@redhat.com> Tested-by: Michal Schmidt <mschmidt@redhat.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Lennart Poettering <lpoetter@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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index bfbd85669694..3eb4dcfc658a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -761,9 +761,6 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p,
struct list_head *dead)
list_move_tail(&p->sibling, &p->real_parent->children);
- if (p->exit_state == EXIT_DEAD)
- return;
* If this is a threaded reparent there is no need to
* notify anyone anything has happened.
@@ -771,9 +768,19 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p,
if (same_thread_group(p->real_parent, father))
- /* We don't want people slaying init. */
+ /*
+ * We don't want people slaying init.
+ *
+ * Note: we do this even if it is EXIT_DEAD, wait_task_zombie()
+ * can change ->exit_state to EXIT_ZOMBIE. If this is the final
+ * state, do_notify_parent() was already called and ->exit_signal
+ * doesn't matter.
+ */
p->exit_signal = SIGCHLD;
+ if (p->exit_state == EXIT_DEAD)
+ return;
/* If it has exited notify the new parent about this child's death. */
if (!p->ptrace &&
p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {