Re: [patch] __block_write_full_page bug
From: Nick Piggin (nickpiggin_at_yahoo.com.au)
Date: 04/26/05
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To: Andrew Morton <akpm@osdl.org> Date: Tue, 26 Apr 2005 22:00:20 +1000
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.
> Was an ENOSPC involved?
>
No.
> Those tests for buffer_async_write(bh) are redundant now, aren't they?
They are, yes. Sorry I noticed that earlier too - they should probably
be BUG_ON(!buffer_async_write(bh)) instead. Would make things clearer.
Nick
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