Messages in this thread | | | Date | Wed, 10 Sep 2008 10:37:49 +0200 | From | Ingo Molnar <> | Subject | Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's mmap_sem... |
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* Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> On Wednesday 10 September 2008 17:57, Peter Zijlstra wrote: > > On Wed, 2008-09-10 at 14:07 +1000, Nick Piggin wrote: > > > On Wednesday 10 September 2008 07:03, Daniel J Blueman wrote: > > > > I observed this locking violation [1] while gnome-panel was loading; > > > > this was previously reported at > > > > http://uwsg.iu.edu/hypermail/linux/kernel/0806.3/2881.html . > > > > > > > > Let me know for more information/config/testing. Thanks! > > > > > > Thanks for the report. I've attached a patch you could test. It compiles > > > (and boots a UML here) but I don't think I've actually tested the inotify > > > path at all, so it may explode on you. > > > > > > Peter, this copy_*_user stuff is quite a nightmare... Well actually it > > > isn't, if the code is designed with it in mind from the start, but it is > > > easy for people to forget it can take mmap_sem and filesystem locks... Is > > > there a way to annotate it and say "might take mmap_sem for read" for > > > example? So that these LORs will _always_ trigger rather than just once > > > in a million times when the reclaim gods frown on us? > > > > Sure, how about the below - untested - uncompiled, might eat kittens, > > etc.. > > > > Just sprinkle something like: > > > > might_lock_read(&mm->mmap_sem); > > > > in the right places. > > Ahh, very nice, thanks! I'll give that a try...
cool! Please send in an RFC patch once you have something that boots - we can stick it into tip/core/locking and see whether there's any new messages on a wide range of systems and workloads. (and we'd also check whether the number of kittens is an invariant.)
Ingo
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