From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>,
linux-xfs@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] block: fix 32 bit overflow in __blkdev_issue_discard()
Date: Wed, 14 Nov 2018 18:51:47 -0700 [thread overview]
Message-ID: <80b9c4b7-1625-a1b6-0f1e-94de9d8b446b@kernel.dk> (raw)
In-Reply-To: <20181115010651.GD32603@ming.t460p>
On 11/14/18 6:06 PM, Ming Lei wrote:
> On Wed, Nov 14, 2018 at 08:18:24AM -0700, Jens Axboe wrote:
>> On 11/13/18 2:43 PM, Dave Chinner wrote:
>>> From: Dave Chinner <dchinner@redhat.com>
>>>
>>> A discard cleanup merged into 4.20-rc2 causes fstests xfs/259 to
>>> fall into an endless loop in the discard code. The test is creating
>>> a device that is exactly 2^32 sectors in size to test mkfs boundary
>>> conditions around the 32 bit sector overflow region.
>>>
>>> mkfs issues a discard for the entire device size by default, and
>>> hence this throws a sector count of 2^32 into
>>> blkdev_issue_discard(). It takes the number of sectors to discard as
>>> a sector_t - a 64 bit value.
>>>
>>> The commit ba5d73851e71 ("block: cleanup __blkdev_issue_discard")
>>> takes this sector count and casts it to a 32 bit value before
>>> comapring it against the maximum allowed discard size the device
>>> has. This truncates away the upper 32 bits, and so if the lower 32
>>> bits of the sector count is zero, it starts issuing discards of
>>> length 0. This causes the code to fall into an endless loop, issuing
>>> a zero length discards over and over again on the same sector.
>>
>> Applied, thanks. Ming, can you please add a blktests test for
>> this case? This is the 2nd time it's been broken.
>
> OK, I will add zram discard test in blktests, which should cover the
> 1st report. For the xfs/259, I need to investigate if it is easy to
> do in blktests.
null_blk has discard support, might be an easier target in terms
of blktests.
--
Jens Axboe
prev parent reply other threads:[~2018-11-15 11:57 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-13 21:43 [PATCH] block: fix 32 bit overflow in __blkdev_issue_discard() Dave Chinner
2018-11-14 2:36 ` Darrick J. Wong
2018-11-14 2:53 ` Ming Lei
2018-11-14 8:08 ` Dave Chinner
2018-11-14 8:15 ` Ming Lei
2018-11-14 15:18 ` Jens Axboe
2018-11-15 1:06 ` Ming Lei
2018-11-15 1:22 ` Dave Chinner
2018-11-15 3:10 ` Ming Lei
2018-11-15 22:13 ` Dave Chinner
2018-11-15 22:24 ` Darrick J. Wong
2018-11-16 4:04 ` Dave Chinner
2018-11-16 8:32 ` Christoph Hellwig
2018-11-16 8:46 ` Omar Sandoval
2018-11-16 8:53 ` Christoph Hellwig
2018-11-16 12:06 ` Ming Lei
2018-11-15 1:51 ` Jens Axboe [this message]
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