Re: [PATCH 1/1] do not abuse ->cred_guard_mutex in threadgroup_lock()

From: Li Zefan
Date: Sun Mar 10 2013 - 21:51:54 EST

On 2013/3/10 4:01, Oleg Nesterov wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Acked-by: Li Zefan <lizefan@xxxxxxxxxx>

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at