Messages in this thread Patch in this message | | | Subject | Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's mmap_sem... | From | Peter Zijlstra <> | Date | Wed, 10 Sep 2008 09:57:35 +0200 |
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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.
--- Subject: lockdep: might_lock annotation
useful to establish a lock dependency in case the actual dependency is rare or hard to trigger.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 331e5f1..0aa657a 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -480,4 +480,22 @@ static inline void print_irqtrace_events(struct task_struct *curr) # define lock_map_release(l) do { } while (0) #endif +#ifdef CONFIG_PROVE_LOCKING +# define might_lock(lock) \ +do { \ + typecheck(struct lockdep_map *, &(lock)->dep_map); \ + lock_acquire(&(lock)->dep_map, 0, 0, 0, 2, NULL, _THIS_IP_); \ + lock_release(&(lock)->dep_map, 0, _THIS_IP_); \ +} while (0) +# define might_lock_read(lock) \ +do { \ + typecheck(struct lockdep_map *, &(lock)->dep_map); \ + lock_acquire(&(lock)->dep_map, 0, 0, 1, 2, NULL, _THIS_IP_); \ + lock_release(&(lock)->dep_map, 0, _THIS_IP_); \ +} while (0) +#else +# define might_lock(lock) do { } while (0) +# define might_lock_read(lock) do { } while (0) +#endif + #endif /* __LINUX_LOCKDEP_H */
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