Messages in this thread | | | Date | Tue, 26 Apr 2005 05:47:29 -0700 | From | Andrew Morton <> | Subject | Re: [patch] __block_write_full_page bug |
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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.
<looks>
Were you using nobh? I guess not. What's to stop the new mpage_writepage() from trying to write a page which is already under PageWriteback()?
I don't think we understand this bug yet. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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