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

I still haven't gotten hold of an i915 machine where I could
run the actua ltest suite.

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?

Note that implementing RQF_PM for blk-mq shouldn't be too hard either,
but if we don't get rid of the nr_pending counter somehow it would
be a severe performance penalty for all scsi devices.

First, tested that next-20170717 still triggers the problem when no 
extra options given. Adding scsi_mod.use_blk_mq=0 makes tests work.

Then I tried with sd.diff patched next-20170717. Works (still) with 
use_blk_mq=0. Also works when no options given, so this patch avoids the 
hang when using the new block-mq.

These tests on generic Haswell 4790K desktop machine.

Best regards,

Tomi
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