On Sat, Feb 19, 2022 at 09:18:58AM -0700, Jens Axboe wrote:

On 2/18/22 8:10 PM, Luis Chamberlain wrote:

quoted

I noticed that since next-20220211 losetup fails at something stupid
simple:

losetup $LOOPDEV $DISK

I can't see how the changes on drivers/block/loop.c would cause this,
I even tried to revert what I thought would be the only commit which
would seem to do a functional change "loop: revert "make autoclear
operation asynchronous" but that didn't fix it.

I proceeded to bisecting... but I did this on today's linux-next,
and well today's linux-next is hosed even at boot. My bisection then
was completley inconclusive since linux-next is pure poop today.

Any ideas though?

Fortunately Linus' tree is fine.

I'm quit afraid that we wouldn't have caught this issue. Seems pretty
straight forward. It would seem we don't have such a basic thing on
blktests, so I'll go add that...

My guess would be that it's:

commit fbdee71bb5d8d054e1bdb5af4c540f2cb86fe296
Author: Christoph Hellwig [off-list ref]
Date:   Tue Jan 4 08:16:47 2022 +0100

    block: deprecate autoloading based on dev_t

Indeed. The issue is that dropping that also does not allow the
association of extra custom higher number loop block nodes created manually
even if you *do* load a respective module before use. That is by design
by the commit, since we're stuffing the nasty old probe logic now under the new
CONFIG_BLOCK_LEGACY_AUTOLOAD. Subtle difference, but same deprecation
effect.

I agree with the approach to stuff all this nasty cruft under
BLOCK_LEGACY_AUTOLOAD however I suspect v5.19 might be too soon to tell if we
can nuke it safely by then though.

I'd go so far as to say that we should sadly make
BLOCK_LEGACY_AUTOLOAD=y for a while before going with an axe to kill it.
I think we have a few hidden gems we'll soon discover might need a bit
more time to adjust.

FWIW below is a simple test, which now fails to explain what I mean with
the above.

root@kdevops ~ # cat loop-high-devs.sh 
#!/bin/bash

NUM="8"
LOOPDEV="/dev/loop${NUM}"

modprobe loop
sleep 2

if [[ ! -e $LOOPDEV ]]; then
	mknod $LOOPDEV b 7 $NUM
fi

losetup -d $LOOPDEV 2>/dev/null

DISK="test_loop_${NUM}.img"
rm -f $DISK
truncate -s 10M $DISK
losetup $LOOPDEV $DISK
if [ $? -eq 0 ]; then
	echo "$LOOPDEV ready"
else
	echo "$LOOPDEV failed"
fi

  Luis