linux-kernel - Re: [bug] block subsystem related crash with latest -git

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Message-ID: <20071017180218.GQ15552@kernel.dk>
Date:	Wed, 17 Oct 2007 20:02:19 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [bug] block subsystem related crash with latest -git

On Wed, Oct 17 2007, Linus Torvalds wrote:
> 
> 
> On Wed, 17 Oct 2007, Jens Axboe wrote:
> > 
> > OK, it is fine, as long as the sglist is cleared initially. And I don't
> > think there's anyway around that, clearly I didn't think long enough
> > before including the memset() removal from Tomo.
> 
> Ok, I think that one-liner fixes the real bug.
> 
> But I think the rest of your changes are simply bad.
> 
> The fix to block/ll_rw_block.c should likely be something like the 
> appended instead:
> 
>  - remove the "memset()" you had added earlier. It's bogus. It cannot be 
>    the right thing. If the sg list wasn't initialized correctly much 
>    earlier, trying to initialize it late is pointless - it contains crap.

It's required to clear output members (like dma_len and so on), since
some of the IOMU code really wants that initialized.

>  - the old code was fine, but let's initialize "sg" to NULL to make it 
>    clear that the initial value of sg is pointless, and only "next_sg" 
>    matters (since sg had better be assigned from that).

If you prefer the old next_sg approach to my alternative, that is fine
with me. But we do need the memset().

-- 
Jens Axboe

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