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authorOleg Nesterov <oleg@redhat.com>2014-12-10 15:45:24 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-10 17:41:10 -0800
commitdc2fd4b00946751ebd222d366fc64550e4188dc2 (patch)
tree1d05ca2373e4125522b804fdbb458d6d862a8953 /kernel/exit.c
parenta90e984c8a660dd58894a68cc5d9d5cd457d5796 (diff)
downloadlinux-sh-dc2fd4b00946751ebd222d366fc64550e4188dc2.tar.gz
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@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Cc: Sterling Alexander <stalexan@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Roland McGrath <roland@hack.frob.com> 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.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 232c4bc8bcc9..0272305bf855 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -548,7 +548,7 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p,
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(struct task_struct *father)
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);
}
}