On Wed, Aug 22, 2018 at 09:06:40AM +0300, Jarkko Nikula wrote:

On 08/21/2018 04:57 PM, Ming Lei wrote:

quoted

On Tue, Aug 21, 2018 at 04:45:41PM +0300, Jarkko Nikula wrote:

quoted

On 08/21/2018 04:03 PM, Adrian Hunter wrote:

quoted

On 21/08/18 15:37, Jarkko Nikula wrote:

quoted

Hi

I bisected some kind of SDHCI regression to commit 6ce3dd6eec11 ("blk-mq:
issue directly if hw queue isn't busy in case of 'none'") causing dumps
below and one or more systemd-udevd processes being in uninterruptible sleep
state preventing safe reboot/shutdown.

This is from an Intel Baytrail based tablet with integrated eMMC but my
up-to-date Debian/testing rootfs (with systemd) is on USB stick.

It doesn't revert cleanly on today's head 778a33959a8a but issue is gone if
I go to a commit before 6ce3dd6eec11 and occurs at 6ce3dd6eec11.

This was discussed here:

	https://marc.info/?l=linux-block&m=153334717506073&w=2

Coincidentally, I just sent the fix patch:

	https://marc.info/?l=linux-mmc&m=153485326025301&w=2

Cool, it fixed my regression. I tested both on top of 6ce3dd6eec11 and head
778a33959a8a. Maybe you would like to add into your patch another fixes tag
and my tested by:

Fixes: 6ce3dd6eec11 ("blk-mq: issue directly if hw queue isn't busy in case
of 'none'")

If you read the above links carefully, you'd see it is wrong to add the tag of
'Fixes: 6ce3dd6eec11'.

Hmm... why? That commit 6ce3dd6eec11 was clearly regressing on my setup
while Adrian's fix for 81196976ed94 that has been present since v4.16 fixes
my finding too.

I don't know well enough MMC and block layer but if commit 6ce3dd6eec11
revealed an issue from MMC under my configuration I'd call it still a
regression.

6ce3dd6eec11 just makes the original issue to happen easier, and the
root cause is that MMC's stack doesn't support concurrent dispatch for 
SDHCI.

Thanks, 
Ming