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Date:   Tue, 5 Jun 2018 10:45:07 -0400
From:   Mike Snitzer <snitzer@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Kent Overstreet <kent.overstreet@gmail.com>,
        torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: dm: Use kzalloc for all structs with embedded biosets/mempools
Message-ID: <20180605144506.GA13100@redhat.com>
References: <20180605092633.29583-1-kent.overstreet@gmail.com>
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On Tue, Jun 05 2018 at 10:22P -0400,
Jens Axboe <axboe@kernel.dk> wrote:

> On 6/5/18 3:26 AM, Kent Overstreet wrote:
> > mempool_init()/bioset_init() require that the mempools/biosets be zeroed
> > first; they probably should not _require_ this, but not allocating those
> > structs with kzalloc is a fairly nonsensical thing to do (calling
> > mempool_exit()/bioset_exit() on an uninitialized mempool/bioset is legal
> > and safe, but only works if said memory was zeroed.)
> > 
> > Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
> > ---
> > 
> > Linus,
> > 
> > I fucked up majorly on the bioset/mempool conversion - I forgot to check that
> > everything biosets/mempools were being embedded in was actually being zeroed on
> > allocation. Device mapper currently explodes, you'll probably want to apply this
> > patch post haste.
> > 
> > I have now done that auditing, for every single conversion - this patch fixes
> > everything I found. There do not seem to be any incorrect ones outside of device
> > mapper...
> > 
> > We'll probably want a second patch that either a) changes
> > bioset_init()/mempool_init() to zero the passed in bioset/mempool first, or b)
> > my preference, WARN() or BUG() if they're passed memory that isn't zeroed.
> 
> Odd, haven't seen a crash, but probably requires kasan or poisoning to
> trigger anything? Mike's tree also had the changes, since they were based
> on the block tree.
> 
> I can queue this up and ship it later today. Mike, you want to review
> this one?

Yes, looks good.

From the start of revisiting these changes last week, Kent and I
discussed whether it was safe to call mempool_exit() even if
mempool_init() failed or was never called.  He advised that it was so
long as the containing structure was zeroed.  But I forgot to audit that 
aspect.  So this was an oversight by both of us.

DM core uses kvzalloc_node for struct mapped_device and cache, crypt,
integrity, verity-fec and zoned targets are already using kzalloc as
needed.

Acked-by: Mike Snitzer <snitzer@redhat.com>