Messages in this thread |  | | | Date | Tue, 17 Oct 2006 01:24:01 +1000 | | From | Nick Piggin <> | | Subject | pagefault_disable (was Re: [patch 6/6] mm: fix pagecache write deadlocks) |
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(trimming cc list)
Peter Zijlstra wrote: > On Sun, 2006-10-15 at 17:57 +0200, Nick Piggin wrote:
>>Hmm, but you may not be doing a copy*user within the kmap. And you may >>want an atomic copy*user not within a kmap (maybe). >> >>I think it really would be more logical to do it in a wrapper function >>pagefault_disable() pagefault_enable()? ;) > > > I did that one first, but then noticed that most non trivial kmap_atomic > implementations already did the inc_preempt_count()/dec_preempt_count() > thing (except frv which did preempt_disable()/preempt_enable() ?) > > Anyway, here goes: > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
I think this is a good approach. The missed preempt checks could easily have been causing scheduling delays because the usercopy can take up a lot of kernel time.
I don't know that the function should go in filemap.h... uaccess.h seems more appropriate, and had thought the pagefault_disable() be calle directly from within the copy_*_user_inatomic functions themselves, not the filemap helper.
Also, the rest of the kernel tree (mainly uaccess and futexes) should be converted ;)
> Index: linux-2.6/mm/filemap.h > =================================================================== > --- linux-2.6.orig/mm/filemap.h 2006-10-14 20:20:20.000000000 +0200 > +++ linux-2.6/mm/filemap.h 2006-10-15 17:17:45.000000000 +0200 > @@ -21,6 +21,22 @@ __filemap_copy_from_user_iovec_inatomic( > size_t bytes); > > /* > + * By increasing the preempt_count we make sure the arch preempt > + * handler bails out early, before taking any locks, so that the copy > + * operation gets terminated early. > + */ > +pagefault_static inline void disable(void) > +{ > + inc_preempt_count(); > +} > + > +pagefault_static inline void enable(void) > +{ > + dec_preempt_count(); > + preempt_check_resched(); > +}
Interesting prototype ;)
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