Messages in this thread | | | Date | Thu, 18 Sep 2008 11:46:54 -0700 | From | Balbir Singh <> | Subject | Re: [PATCH -mm] memrlimit: fix task_lock() recursive locking |
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Andrea Righi wrote: > cgroup_mm_owner_callbacks() can be called with task_lock() held in > mm_update_next_owner(), and all the .mm_owner_changed callbacks seem to > be *always* called with task_lock() held. > > Actually, memrlimit is using task_lock() via get_task_mm() in > memrlimit_cgroup_mm_owner_changed(), raising the following recursive locking > trace:
[snip]
Thanks for the BUG report()
[snip]
> static void memrlimit_cgroup_mm_owner_changed(struct cgroup_subsys *ss, > struct cgroup *old_cgrp, > @@ -246,7 +246,7 @@ static void memrlimit_cgroup_mm_owner_changed(struct cgroup_subsys *ss, > struct task_struct *p) > { > struct memrlimit_cgroup *memrcg, *old_memrcg; > - struct mm_struct *mm = get_task_mm(p); > + struct mm_struct *mm = get_task_mm_task_locked(p); >
Since we hold task_lock(), we know that p->mm cannot change and we don't have to worry about incrementing mm_users. I think using just p->mm will work, we do have checks to make sure we don't pick a kernel thread. I vote for going down that road.
-- Balbir
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