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authorJames Wang <jnwang@suse.com>2017-06-08 14:52:51 +0800
committerJens Axboe <axboe@fb.com>2017-06-08 08:04:18 -0600
commit6460495709aeb651896bc8e5c134b2e4ca7d34a8 (patch)
tree94bb68a2febbf13aa2295e4161a9c61692bd2441 /drivers/block
parent6679a90c4b0dc2563383df1fe0eb170736952a2e (diff)
downloadlinux-6460495709aeb651896bc8e5c134b2e4ca7d34a8.tar.bz2
Fix loop device flush before configure v3
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>
Diffstat (limited to 'drivers/block')
-rw-r--r--drivers/block/loop.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 28d932906f24..ebbd0c3fe0ed 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -608,6 +608,9 @@ 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);
}