Messages in this thread | | | Date | Thu, 05 Oct 2006 16:28:48 +1000 | From | Nick Piggin <> | Subject | Re: 2.6.18: Kernel BUG at mm/rmap.c:522 |
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Dave Jones wrote: > On Wed, Oct 04, 2006 at 05:49:00PM +0200, Peter Zijlstra wrote: > > > > > It is also nice if we can work out where the page actually came from. The > > > > following attached patch should help out a bit with that, if you could > > > > run with it? > > > Okay. I'll reboot with your patch and let you know if it crashes again. > > enable CONFIG_DEBUG_VM to get that. > > Given this warnings still pops up from time to time, I question whether > putting that check under DEBUG_VM was such a good idea. It's not as > if it's a major performance impact. This has potential for us to lose > valuable debugging info for a few nanoseconds performance increase in > an already costly path.
Frustratingly, it usually doesn't tell us much (without my previous patch), because it is normally some driver that has stuffed up their refcounting and the page-> fields don't tell us where the page has come from.
But..
> This patch brings it back unconditionally, and moves the BUG() > into the if arm.
... this shouldn't hurt if gcc moves the unlikely code out of the linear instruction stream, which I think it usually does. It shouldn't cost _anything_ because we're already doing the branch for the BUG_ON which you remove.
> Signed-off-by: Dave Jones <davej@redhat.com>
Thanks, Acked-by: Nick Piggin <npiggin@suse.de>
> > --- local-git/mm/rmap.c~ 2006-10-04 16:38:06.000000000 -0400 > +++ local-git/mm/rmap.c 2006-10-04 16:38:24.000000000 -0400 > @@ -576,15 +576,14 @@ void page_add_file_rmap(struct page *pag > void page_remove_rmap(struct page *page) > { > if (atomic_add_negative(-1, &page->_mapcount)) { > -#ifdef CONFIG_DEBUG_VM > if (unlikely(page_mapcount(page) < 0)) { > printk (KERN_EMERG "Eeek! page_mapcount(page) went negative! (%d)\n", page_mapcount(page)); > printk (KERN_EMERG " page->flags = %lx\n", page->flags); > printk (KERN_EMERG " page->count = %x\n", page_count(page)); > printk (KERN_EMERG " page->mapping = %p\n", page->mapping); > + BUG(); > } > -#endif > - BUG_ON(page_mapcount(page) < 0); > + > /* > * It would be tidy to reset the PageAnon mapping here, > * but that might overwrite a racing page_add_anon_rmap
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