The patch titled
Subject: exit: reparent: use ->ptrace_entry rather than ->sibling for EXIT_DEAD tasks
has been added to the -mm tree. Its filename is
exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
echo and later at
echo http://ozlabs.org/~akpm/mmotm/broken-out/exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: exit: reparent: use ->ptrace_entry rather than ->sibling for EXIT_DEAD tasks
reparent_leader() reuses ->sibling as a list node to add an EXIT_DEAD task
into dead_children list we are going to release. This obviously removes
the dead task from its real_parent->children list and this is even good;
the parent can do nothing with the EXIT_DEAD reparented zombie, it only
makes do_wait() slower.
But, this also means that it can not be reparented once again, so if its
new parent dies too nobody will update ->parent/real_parent, they can
point to the freed memory even before release_task() we are going to call,
this breaks the code which relies on pid_alive() to access
->real_parent/parent.
Fortunately this is mostly theoretical, this can only happen if init or
PR_SET_CHILD_SUBREAPER process ignores SIGCHLD and the new parent
sub-thread exits right after we drop tasklist_lock.
Change this code to use ->ptrace_entry instead, we know that the child is
not traced so nobody can ever use this member. This also allows to unify
this logic with exit_ptrace(), see the next changes.
Note: we really need to change release_task() to nullify real_parent/
parent/group_leader pointers, but we need to change the current users
first somehow. And it would be better to reap this zombie immediately but
release_task_locked() we need is complicated by proc_flush_task().
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>,
Cc: Sterling Alexander <stalexan@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN kernel/exit.c~exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks kernel/exit.c
--- a/kernel/exit.c~exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks
+++ a/kernel/exit.c
@@ -548,7 +548,7 @@ static void reparent_leader(struct task_
p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
if (do_notify_parent(p, p->exit_signal)) {
p->exit_state = EXIT_DEAD;
- list_move_tail(&p->sibling, dead);
+ list_add(&p->ptrace_entry, dead);
}
}
@@ -587,8 +587,8 @@ static void forget_original_parent(struc
BUG_ON(!list_empty(&father->children));
- list_for_each_entry_safe(p, n, &dead_children, sibling) {
- list_del_init(&p->sibling);
+ list_for_each_entry_safe(p, n, &dead_children, ptrace_entry) {
+ list_del_init(&p->ptrace_entry);
release_task(p);
}
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
mmfs-introduce-helpers-around-the-i_mmap_mutex.patch
mm-use-new-helper-functions-around-the-i_mmap_mutex.patch
mm-convert-i_mmap_mutex-to-rwsem.patch
mm-rmap-share-the-i_mmap_rwsem.patch
uprobes-share-the-i_mmap_rwsem.patch
mm-xip-share-the-i_mmap_rwsem.patch
mm-memory-failure-share-the-i_mmap_rwsem.patch
mm-nommu-share-the-i_mmap_rwsem.patch
mm-memoryc-share-the-i_mmap_rwsem.patch
proc-task_state-read-cred-group_info-outside-of-task_lock.patch
proc-task_state-deuglify-the-max_fds-calculation.patch
proc-task_state-move-the-main-seq_printf-outside-of-rcu_read_lock.patch
proc-task_state-ptrace_parent-doesnt-need-pid_alive-check.patch
sched_show_task-fix-unsafe-usage-of-real_parent.patch
exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
exit-reparent-cleanup-the-changing-of-parent.patch
exit-reparent-cleanup-the-usage-of-reparent_leader.patch
exit-ptrace-shift-reap-dead-code-from-exit_ptrace-to-forget_original_parent.patch
usermodehelper-dont-use-clone_vfork-for-____call_usermodehelper.patch
usermodehelper-kill-the-kmod_thread_locker-logic.patch
linux-next.patch
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