Patch "Fix loop device flush before configure v3" has been added to the 4.4-stable tree

Patch "Fix loop device flush before configure v3" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    Fix loop device flush before configure v3

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fix-loop-device-flush-before-configure-v3.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Apr 10 10:31:53 CEST 2018
From: James Wang <jnwang@suse.com>
Date: Thu, 8 Jun 2017 14:52:51 +0800
Subject: Fix loop device flush before configure v3

From: James Wang <jnwang@suse.com>


[ Upstream commit 6460495709aeb651896bc8e5c134b2e4ca7d34a8 ]

While installing SLES-12 (based on v4.4), I found that the installer
will stall for 60+ seconds during LVM disk scan.  The root cause was
determined to be the removal of a bound device check in loop_flush()
by commit b5dd2f6047ca ("block: loop: improve performance via blk-mq").

Restoring this check, examining ->lo_state as set by loop_set_fd()
eliminates the bad behavior.

Test method:
modprobe loop max_loop=64
dd if=/dev/zero of=disk bs=512 count=200K
for((i=0;i<4;i++))do losetup -f disk; done
mkfs.ext4 -F /dev/loop0
for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done
for f in `ls /dev/loop[0-9]*|sort`; do \
	echo $f; dd if=$f of=/dev/null  bs=512 count=1; \
	done

Test output:  stock          patched
/dev/loop0    18.1217e-05    8.3842e-05
/dev/loop1     6.1114e-05    0.000147979
/dev/loop10    0.414701      0.000116564
/dev/loop11    0.7474        6.7942e-05
/dev/loop12    0.747986      8.9082e-05
/dev/loop13    0.746532      7.4799e-05
/dev/loop14    0.480041      9.3926e-05
/dev/loop15    1.26453       7.2522e-05

Note that from loop10 onward, the device is not mounted, yet the
stock kernel consumes several orders of magnitude more wall time
than it does for a mounted device.
(Thanks for Mike Galbraith <efault@gmx.de>, give a changelog review.)

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: James Wang <jnwang@suse.com>
Fixes: b5dd2f6047ca ("block: loop: improve performance via blk-mq")
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/block/loop.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -623,6 +623,9 @@ static int loop_switch(struct loop_devic
  */
 static int loop_flush(struct loop_device *lo)
 {
+	/* loop not yet configured, no running thread, nothing to flush */
+	if (lo->lo_state != Lo_bound)
+		return 0;
 	return loop_switch(lo, NULL);
 }
 


Patches currently in stable-queue which might be from jnwang@suse.com are

queue-4.4/fix-loop-device-flush-before-configure-v3.patch