linux-kernel - Re: [patch 1/2] block, drbd: fix drbd_req

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Message-ID: <54FB9FE2.5040707@fb.com>
Date:	Sat, 7 Mar 2015 18:03:30 -0700
From:	Jens Axboe <axboe@...com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Lars Ellenberg <drbd-dev@...ts.linbit.com>,
	<linux-kernel@...r.kernel.org>, <drbd-user@...ts.linbit.com>
Subject: Re: [patch 1/2] block, drbd: fix drbd_req_new() initialization

On 03/07/2015 05:53 PM, David Rientjes wrote:
> On Sat, 7 Mar 2015, Jens Axboe wrote:
> 
>>> mempool_alloc() does not support __GFP_ZERO since elements may come from
>>> memory that has already been released by mempool_free().
>>>
>>> Remove __GFP_ZERO from mempool_alloc() in drbd_req_new() and properly
>>> initialize it to 0.
>>
>> You should add it to mempool instead, avoid having this issue show up for
>> other folks as well. It'd be trivial to do. Normal ->alloc() should honor
>> __GFP_ZERO, just do the same manually for removing an item from the internal
>> pool.
>>
> 
> Umm, it's not trivial to do and wouldn't make sense to do it.  Mempools 

Uhm, it would make sense, though.

> don't know the element size, in other words it wouldn't know the length to 
> memset() to 0 for mempool_alloc().  It shouldn't be modified to know the 
> element size since elements are allocated by the implementation of 
> mempool_alloc_t and they could easily become inconsistent.  This patch is 
> what you want to merge, really.
> 

I forgot we don't have the size in there. Then I would suggest adding a
WARN_ON() for __GFP_ZERO being set in mempool_alloc(), at the very least.

-- 
Jens Axboe

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