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Date: Fri, 8 Dec 2000 14:42:51 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: Alexander Viro <viro@math.psu.edu>
cc: David Woodhouse <dwmw2@infradead.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Re: kernel BUG at buffer.c:827 in test12-pre6 and 7 
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On Fri, 8 Dec 2000, Alexander Viro wrote:
> 
> I'm quite aware of that fact ;-) However, you said 
> 
>    On the other hand, I have this suspicion that there is an even simpler
>    solution: stop using the end_buffer_io_sync version for writes
>    altogether.
> 
> If that happens (i.e. if write requests resulting from prepare_write()/
> commit_write()/bdflush sequence become async) we must stop unlocking pages
> after commit_write(). Essentially it would become unlocker of the same
> kind as readpage() and writepage() - callers must assume that page submitted
> to commit_write() will eventually be unlocked.

You're right, we can't do that for anonymous buffers right now. Mea culpa.

Looking more at this issue, I suspect that the easiest pretty solution
that everybody can probably agree is reasonable is to either pass down the
end-of-io callback to ll_rw_block as you suggested, or, preferably by just
forcing the _caller_ to do the buffer locking, and just do the b_end_io
stuff inside the buffer lock and get rid of all the races that way
instead (and make ll_rw_block() verify that the buffers it is passed are
always locked).

		Linus

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