Messages in this thread | | | Date | Fri, 8 Jun 2007 12:32:30 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 1/3] [PATCH i386] during VM oom condition, kill all threads in process group |
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On Fri, 08 Jun 2007 14:19:18 -0500 Will Schmidt <will_schmidt@vnet.ibm.com> wrote:
> > > > zap_other_threads() requires tasklist_lock. > > Yup, I missed that. Thanks for pointing it out. > > > > > > > > > If we're going to do this then we should probably create some new function > > > > (with a better name) which takes tasklsit_lock and then calls > > > > zap_other_threads(). > > I expect this will be a write_lock_irq() since zap_other_threads will be > doing a bit more than just reading the task info.
No, I think read_lock() will be sufficient.
In fact, it's probably the case that rcu_read_lock() is now sufficient locking coverage for zap_other_threads() (cc's people).
It had better be, because do_group_exit() forgot to take tasklist_lock. It is perhaps relying upon spin_lock()'s hidden rcu_read_lock() properties without so much as a code comment, which would be somewhat nasty of it.
You could perhaps just call do_group_exit() from within the fault handler, btw.
> This will be down in a do-page-fault failure path (see > arch/*/mm/fault.c). I wonder if calling write_lock is going to be safe, > or if its possible to get into a deadlock? i.e. should I branch back up > to the survive: label if I can't take the lock? Would that even be > sufficient? or is it not an issue here?
You can take the lock in the fault handler. Nobody should be getting pagefaults while holding tasklist_lock. (Well, a vmalloc fault might, but that's a special-case which doesn't allocate memory or anything like that).
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