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authorOleg Nesterov <oleg@redhat.com>2013-04-30 15:28:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-04-30 17:04:07 -0700
commite56fb2874015370e3b7f8d85051f6dce26051df9 (patch)
tree0820c06eb4a25daf65734412af139e98ac1649c8 /fs
parent12eaaf309a798973d215f7f21aa5a67a760ed7c8 (diff)
downloadlinux-e56fb2874015370e3b7f8d85051f6dce26051df9.tar.gz
exec: do not abuse ->cred_guard_mutex in threadgroup_lock()
threadgroup_lock() takes signal->cred_guard_mutex to ensure that thread_group_leader() is stable. This doesn't look nice, the scope of this lock in do_execve() is huge. And as Dave pointed out this can lead to deadlock, we have the following dependencies: do_execve: cred_guard_mutex -> i_mutex cgroup_mount: i_mutex -> cgroup_mutex attach_task_by_pid: cgroup_mutex -> cred_guard_mutex Change de_thread() to take threadgroup_change_begin() around the switch-the-leader code and change threadgroup_lock() to avoid ->cred_guard_mutex. Note that de_thread() can't sleep with ->group_rwsem held, this can obviously deadlock with the exiting leader if the writer is active, so it does threadgroup_change_end() before schedule(). Reported-by: Dave Jones <davej@redhat.com> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 260f89f6665..963f510a25a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -898,11 +898,13 @@ static int de_thread(struct task_struct *tsk)
sig->notify_count = -1; /* for exit_notify() */
for (;;) {
+ threadgroup_change_begin(tsk);
write_lock_irq(&tasklist_lock);
if (likely(leader->exit_state))
break;
__set_current_state(TASK_KILLABLE);
write_unlock_irq(&tasklist_lock);
+ threadgroup_change_end(tsk);
schedule();
if (unlikely(__fatal_signal_pending(tsk)))
goto killed;
@@ -960,6 +962,7 @@ static int de_thread(struct task_struct *tsk)
if (unlikely(leader->ptrace))
__wake_up_parent(leader, leader->parent);
write_unlock_irq(&tasklist_lock);
+ threadgroup_change_end(tsk);
release_task(leader);
}