[dm-devel] block: eliminate potential for infinite loop in blkdev_issue_discard

[Jens Axboe]

On 2010-10-14 23:37, Mike Snitzer wrote:
> On Mon, Sep 27 2010 at  2:13pm -0400,
> Mike Snitzer <snitzer at redhat.com> wrote:
> 
>> Due to the recently identified overflow in read_capacity_16() it was
>> possible for max_discard_sectors to be zero but still have discards
>> enabled on the associated device's queue.
>>
>> Eliminate the possibility for blkdev_issue_discard to infinitely loop.
>>
>> Interestingly this issue wasn't identified until a device, whose
>> discard_granularity was 0 due to read_capacity_16 overflow, was consumed
>> by blk_stack_limits() to construct limits for a higher-level DM
>> multipath device.  The multipath device's resulting limits never had the
>> discard limits stacked because blk_stack_limits() will only do so if
>> the bottom device's discard_granularity != 0.  This resulted in the
>> multipath device's limits.max_discard_sectors being 0.
> 
> Hi Jens,
> 
> This patch would only serve as a future safety-net now that the
> elimination of the overflow in read_capacity_16() has been staged for
> 2.6.37.  Defensive programming and all...
> 
> What do you (and others) think about this patch?

Agree, may as well play it safe(r).

-- 
Jens Axboe