linux-kernel - Re: [dm-devel] [PATCH v10 1/8] block: Generalized bio pool freeing

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Message-ID: <20120918163156.GC17356@agk-dp.fab.redhat.com>
Date:	Tue, 18 Sep 2012 17:31:57 +0100
From:	Alasdair G Kergon <agk@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Jens Axboe <axboe@...nel.dk>,
	Lars Ellenberg <lars.ellenberg@...bit.com>,
	Hannes Reinecke <hare@...e.de>
Subject: Re: [dm-devel] [PATCH v10 1/8] block: Generalized bio pool freeing

On Mon, Sep 17, 2012 at 01:51:39PM -0700, Kent Overstreet wrote:
> That isn't a very good patch - it says it's clearing bi_end_io as a
> precaution, but as a precaution to what?
 
As a precaution against the endio function being called an extra time by
mistake if a stray reference remains after the bio has been freed.
Wipe this field when dm frees it.  Defensive programming, basically,
in response to a tricky bug he had to deal with.

Alasdair

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