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@hua...
V2:
- run .cleanup_rq() in blk_mq_free_request(), as suggested by Mike