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Re: [dm-devel] [PATCH 0/3] Fix SMP races in dm-crypt



On Thu, 22 Mar 2007 21:28:16 +0100
Christophe Saout <christophe saout de> wrote:

> Hi Olaf,

err, which Olaf are you addressing?  He is not cc'ed.

> > (I'm resending this, because it seems mailman ate this posting
> > the first time around - apologies if you're seeing this twice).
> > 
> > I investigated kernel Bug 5948 (Oops when accessing SATA with device mapper on
> > AMD 64 X2) to help cut down on the number of open bugs.
> > 
> > The problem reported in that bug seems to be caused by memory pressure
> > when writing - crypt_alloc_buffer can return less than the full number of
> > pages required. In that case, the bio is split, but we're keeping a pointer
> > to the first chunk of the request around in first_clone, and copy it. If the
> > first clone completes I/O while we're cloning it, we oops on garbage in
> > the bvec.
> > 
> > I was able to reproduce this on 2.6.20 - and the following patches
> > seem to fix it for me.
> > 
> > dm-crypt-clone_init-early
> > 	We need to call clone_init early on, before we can conceivably
> > 	ever call bio_put on the clone
> > 
> > dm-crypt-clone-race
> > 	Do no access bios after generic_make_request
> > 
> > dm-crypt-drop-first_clone
> > 	Drop the first_clone business, and always allocate a fresh bio.
> 
> I fully agree. I didn't notice when the sharing of the bvec went away,
> but it's no longer needed and the code is simpler. As for the other two
> - ouch, you're right.
> 
> Thanks for investigating fixing these things.
> 
> All four patches are
> 
> Acked-By: Christophe Saout <christophe saout de>

I'm hunting around, but cannot find the patches to which you refer.  Maybe
they're on dm-devel only?


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