On 17 July 2017 at 18:18, Evangelos Foutras [off-list ref] wrote:

On 17/07/17 10:53, Christoph Hellwig wrote:

quoted

But I did some audit of the code, and it seems blk-mq is lacking
support for the RQF_PM flag.  While I can't directly see how
this would cause the hang your caused it's a least easy to test.

Can you apply the patch below and test with the use_blk_mq=0 parameter?

I think the patch needs to be tested with scsi_mod.use_blk_mq=1 (which I
will try to do and report back).

I briefly tested the patch (on top of Linux 4.12.2) and it appears to
successfully work around the issue; my laptop happily resumes from S3
and can access the HDD.