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 --- drivers/block/loop.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 3e65ae144fde..1dd16f26e77d 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -623,6 +623,9 @@ static int loop_switch(struct loop_device *lo, struct file *file) */ 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); }