Messages in this thread |  | | | Date | Wed, 27 Apr 2005 10:10:19 +1000 | | From | Nick Piggin <> | | Subject | Re: [patch] __block_write_full_page bug |
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Andrew Morton wrote: > Nick Piggin <nickpiggin@yahoo.com.au> wrote: > >>On Tue, 2005-04-26 at 04:50 -0700, Andrew Morton wrote: >> > Nick Piggin <nickpiggin@yahoo.com.au> wrote: >> > > >> > > When running >> > > fsstress -v -d $DIR/tmp -n 1000 -p 1000 -l 2 >> > > on an ext2 filesystem with 1024 byte block size, on SMP i386 with 4096 byte >> > > page size over loopback to an image file on a tmpfs filesystem, I would >> > > very quickly hit >> > > BUG_ON(!buffer_async_write(bh)); >> > > in fs/buffer.c:end_buffer_async_write >> > > >> > > It seems that more than one request would be submitted for a given bh >> > > at a time. __block_write_full_page looks like the culprit - with the >> > > following patch things are very stable. >> > >> > What's the bug? I don't see it. >> > >> >> Ah, the bug is that end_buffer_async_write first does >> BUG_ON(!buffer_async_write(bh)); >> then a bit later does >> clear_buffer_async_write(bh); >> >> That's where it was blowing up for me, because end_buffer_async_write >> was being run twice for that buffer. >> >> Or did you mean *how* is it being run twice? I didn't exactly find >> the stack traces involved, but I imagine that simply testing >> buffer_async_write catches other requests in flight - ie. we've >> lost track of exactly which ones we own. >> > > > How can such a thing come about? Both PageLocked() and PageWriteback() are > supposed to stop new writeback being started against the page. >
You have a point.
> <looks> > > Were you using nobh? I guess not. What's to stop the new
No
> mpage_writepage() from trying to write a page which is already under > PageWriteback()? >
Don't know... I didn't think mapping->writepage should be called for a PageWriteback page?
> I don't think we understand this bug yet. >
It appears not. I'll look into it further.
-- SUSE Labs, Novell Inc.
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