korg/linux
0
0
Fork 0
mirror of https://mirrors.bfsu.edu.cn/git/linux.git synced 2024-11-26 21:54:11 +08:00
Code Issues Packages Projects Releases Wiki Activity

block: fix race between adding/removing rq qos and normal IO

Browse Source 
Yi reported several kernel panics on:

[16687.001777] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
...
[16687.163549] pc : __rq_qos_track+0x38/0x60

or

[  997.690455] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
...
[  997.850347] pc : __rq_qos_done+0x2c/0x50

Turns out it is caused by race between adding rq qos(wbt) and normal IO
because rq_qos_add can be run when IO is being submitted, fix this issue
by freezing queue before adding/deleting rq qos to queue.

rq_qos_exit() needn't to freeze queue because it is called after queue
has been frozen.

iolatency calls rq_qos_add() during allocating queue, so freezing won't
add delay because queue usage refcount works at atomic mode at that
time.

iocost calls rq_qos_add() when writing cgroup attribute file, that is
fine to freeze queue at that time since we usually freeze queue when
storing to queue sysfs attribute, meantime iocost only exists on the
root cgroup.

wbt_init calls it in blk_register_queue() and queue sysfs attribute
store(queue_wb_lat_store() when write it 1st time in case of !BLK_WBT_MQ),
the following patch will speedup the queue freezing in wbt_init.

Reported-by: Yi Zhang <yi.zhang@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Link: https://lore.kernel.org/r/20210609015822.103433-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2021-06-09 09:58:21 +08:00 committed by Jens Axboe
parent 6a03cd9843
commit 2cafe29a8d
1 changed files with 24 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
block/blk-rq-qos.h
View File

@ -7,6 +7,7 @@
#include <linux/blk_types.h>
#include <linux/atomic.h>
#include <linux/wait.h>
#include <linux/blk-mq.h>
#include "blk-mq-debugfs.h"
@ -99,8 +100,21 @@ static inline void rq_wait_init(struct rq_wait *rq_wait)
static inline void rq_qos_add(struct request_queue *q, struct rq_qos *rqos)
{
/*
* No IO can be in-flight when adding rqos, so freeze queue, which
* is fine since we only support rq_qos for blk-mq queue.
*
* Reuse ->queue_lock for protecting against other concurrent
* rq_qos adding/deleting
*/
blk_mq_freeze_queue(q);
spin_lock_irq(&q->queue_lock);
rqos->next = q->rq_qos;
q->rq_qos = rqos;
spin_unlock_irq(&q->queue_lock);
blk_mq_unfreeze_queue(q);
if (rqos->ops->debugfs_attrs)
blk_mq_debugfs_register_rqos(rqos);
@ -110,12 +124,22 @@ static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
{
struct rq_qos **cur;
/*
* See comment in rq_qos_add() about freezing queue & using
* ->queue_lock.
*/
blk_mq_freeze_queue(q);
spin_lock_irq(&q->queue_lock);
for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
if (*cur == rqos) {
*cur = rqos->next;
break;
}
}
spin_unlock_irq(&q->queue_lock);
blk_mq_unfreeze_queue(q);
blk_mq_debugfs_unregister_rqos(rqos);
}