| From foo@baz Mon Apr 9 17:09:24 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 |
| @@ -612,6 +612,9 @@ 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); |
| } |
| |