Re: [PATCH V2 0/2] block/scsi/dm-rq: fix leak of request private data in dm-mpath

[Benjamin Block <bblock@linux.ibm.com>]

Hey Ming Lei,

On Sat, Jul 20, 2019 at 11:06:35AM +0800, Ming Lei wrote:
> Hi,
> 
> When one request is dispatched to LLD via dm-rq, if the result is
> BLK_STS_*RESOURCE, dm-rq will free the request. However, LLD may allocate
> private data for this request, so this way will cause memory leak.

I am confused about this. Probably because I am not up-to-date with
all of blk-mq. But if you free the LLD private data before the request
is finished, what is the LLD doing if the request finishes afterwards?
Would that not be an automatic use-after-free?

> 
> Add .cleanup_rq() callback and implement it in SCSI for fixing the issue,
> since SCSI is the only driver which allocates private requst data in
> .queue_rq() path.
> 
> Another use case of this callback is to free the request and re-submit
> bios during cpu hotplug when the hctx is dead, see the following link:
> 
> https://lore.kernel.org/linux-block/f122e8f2-5ede-2d83-9ca0-bc713ce66d01@huawei.com/T/#t
> 
> V2:
> 	- run .cleanup_rq() in blk_mq_free_request(), as suggested by Mike 

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IBM Systems & Technology Group   /  IBM Deutschland Research & Development GmbH
Vorsitz. AufsR.: Matthias Hartmann       /      Geschäftsführung: Dirk Wittkopp
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