Re: [PATCH] block: blk-mq-sched: Replace GFP_ATOMIC with GFP_KERNEL in blk_mq_sched_assign_ioc

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Jan 25, 2018 at 10:46:26AM +0800, Jia-Ju Bai wrote:
> The function ioc_create_icq here is not called in atomic context.
> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
> 
> This is found by a static analysis tool named DCNS written by myself.

Umm...  Some human-readable analysis would be welcome.  FWIW, I've tried to
put a proof together, but...
	struct blk_mq_ops->timeout = nvme_timeout
	nvme_timeout()
		nvme_alloc_request()
			blk_mq_alloc_request_hctx()
				blk_mq_get_request()
					blk_mq_sched_assign_ioc()
... and while I have not traced the call chain further, the look of that
function (nvme_timeout()) strongly suggests that it *is* meant to be
called from bloody atomic context.

"My tool has found that place/put together a proof" is nice, but it
doesn't replace the proof itself...