@@ -559,9 +559,6 @@ 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.
@@ -569,9 +566,19 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p,
if (same_thread_group(p->real_parent, father))
return;
- /* 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)) {
This is a note to let you know that I have just added a patch titled wait: fix reparent_leader() vs EXIT_DEAD->EXIT_ZOMBIE race to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.11.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 5124318ee2679a92978c5d4e5a94d6156939091a Mon Sep 17 00:00:00 2001 From: Oleg Nesterov <oleg@redhat.com> Date: Mon, 7 Apr 2014 15:38:41 -0700 Subject: 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: Luis Henriques <luis.henriques@canonical.com> --- kernel/exit.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) -- 1.9.1