Hi Bart On 06/21/2018 12:18 AM, Bart Van Assche wrote: > On Wed, 2018-06-20 at 10:09 +0800, jianchao.wang wrote: >> It is very easy to reproduce with following scripts. >> >> script 0 >> while true >> do >> modprobe null_blk queue_mode=2 shared_tags=1 >> sleep 0.1 >> rmmod null_blk >> sleep 0.1 >> done >> >> script 1 >> file0="/sys/block/nullb0/mq/0/nr_tags" >> file1="/sys/block/nullb0/mq/0/cpu0/rq_list" >> while true; >> do >> if [ -e $file0 ];then >> cat $file0 >> fi >> if [ -e $file1 ];then >> cat $file1 >> fi >> done > > Hello Jianchao, > > Thanks for having shared a reproducer. However, the approach of the patch you > posted doesn't seem like the right approach to me. I propose to proceed as > follows: > * Convert the reproducer into a blktests test and submit is as a patch to the > blktests project (https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_osandov_blktests&d=DwIGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26ATvfo6QSTvZyQ&m=_TjwODcX-0o-OZfrVTFMpvbS0QbYxoya17aHM9pZAXw&s=wdVpTkE6PJX3GXvjXNwEup3opdflyCGY324CAYXSixY&e=). > * Remove the mutex_lock/unlock(&sysfs_lock) calls from blk_cleanup_queue(). > These calls are useless. Block drivers are required to call del_gendisk() > before calling blk_cleanup_queue(). That means that sysfs attributes are > removed synchronously before blk_cleanup_queue() is called. The following > statement in blk_cleanup_queue() verifies that: > WARN_ON_ONCE(q->kobj.state_in_sysfs); > BTW, this also means that the blk_queue_dying() checks in various show and > store methods are superfluous. > * Introduce a new mutex to serialize blk_mq_register_dev() and > blk_mq_sysfs_register() and blk_mq_sysfs_unregister(). I think it is wrong > that these functions use sysfs_mutex. > * Document the purpose of sysfs_mutex in include/linux/blkdev.h, namely to > serialize the sysfs .show() and .store() callback functions and also to > serialize elevator changes. > Really appreciate your kindly and detailed directive. I will post the V2 version based on your suggestions later. Thanks Jianchao > > >
