Freezing the request queue from inside sysfs store callbacks may cause a
deadlock in combination with the dm-multipath driver and the
queue_if_no_path option. Additionally, freezing the request queue slows
down system boot on systems where sysfs attributes are set synchronously.
Fix this by removing the blk_mq_freeze_queue() / blk_mq_unfreeze_queue()
calls from the store callbacks that do not strictly need these callbacks.
This patch may cause a small delay in applying the new settings.
This patch affects the following sysfs attributes:
* io_poll_delay
* io_timeout
* nomerges
* read_ahead_kb
* rq_affinity
Here is an example of a deadlock triggered by running test srp/002:
task:multipathd
Call Trace:
<TASK>
__schedule+0x8c1/0x1bf0
schedule+0xdd/0x270
schedule_preempt_disabled+0x1c/0x30
__mutex_lock+0xb89/0x1650
mutex_lock_nested+0x1f/0x30
dm_table_set_restrictions+0x823/0xdf0
__bind+0x166/0x590
dm_swap_table+0x2a7/0x490
do_resume+0x1b1/0x610
dev_suspend+0x55/0x1a0
ctl_ioctl+0x3a5/0x7e0
dm_ctl_ioctl+0x12/0x20
__x64_sys_ioctl+0x127/0x1a0
x64_sys_call+0xe2b/0x17d0
do_syscall_64+0x96/0x3a0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
</TASK>
task:(udev-worker)
Call Trace:
<TASK>
__schedule+0x8c1/0x1bf0
schedule+0xdd/0x270
blk_mq_freeze_queue_wait+0xf2/0x140
blk_mq_freeze_queue_nomemsave+0x23/0x30
queue_ra_store+0x14e/0x290
queue_attr_store+0x23e/0x2c0
sysfs_kf_write+0xde/0x140
kernfs_fop_write_iter+0x3b2/0x630
vfs_write+0x4fd/0x1390
ksys_write+0xfd/0x230
__x64_sys_write+0x76/0xc0
x64_sys_call+0x276/0x17d0
do_syscall_64+0x96/0x3a0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
</TASK>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Nilay Shroff <nilay@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: af2814149883 ("block: freeze the queue in queue_attr_store")
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/blk-sysfs.c | 16 +---------------
1 file changed, 1 insertion(+), 15 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index b2b9b89d6967..ab34fe62f4da 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -105,7 +105,6 @@ queue_ra_store(struct gendisk *disk, const char *page, size_t count)
{
unsigned long ra_kb;
ssize_t ret;
- unsigned int memflags;
struct request_queue *q = disk->queue;
ret = queue_var_store(&ra_kb, page, count);
@@ -116,10 +115,8 @@ queue_ra_store(struct gendisk *disk, const char *page, size_t count)
* calculated from the queue limits by queue_limits_commit_update.
*/
mutex_lock(&q->limits_lock);
- memflags = blk_mq_freeze_queue(q);
disk->bdi->ra_pages = ra_kb >> (PAGE_SHIFT - 10);
mutex_unlock(&q->limits_lock);
- blk_mq_unfreeze_queue(q, memflags);
return ret;
}
@@ -317,21 +314,18 @@ static ssize_t queue_nomerges_store(struct gendisk *disk, const char *page,
size_t count)
{
unsigned long nm;
- unsigned int memflags;
struct request_queue *q = disk->queue;
ssize_t ret = queue_var_store(&nm, page, count);
if (ret < 0)
return ret;
- memflags = blk_mq_freeze_queue(q);
blk_queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
blk_queue_flag_clear(QUEUE_FLAG_NOXMERGES, q);
if (nm == 2)
blk_queue_flag_set(QUEUE_FLAG_NOMERGES, q);
else if (nm)
blk_queue_flag_set(QUEUE_FLAG_NOXMERGES, q);
- blk_mq_unfreeze_queue(q, memflags);
return ret;
}
@@ -351,7 +345,6 @@ queue_rq_affinity_store(struct gendisk *disk, const char *page, size_t count)
#ifdef CONFIG_SMP
struct request_queue *q = disk->queue;
unsigned long val;
- unsigned int memflags;
ret = queue_var_store(&val, page, count);
if (ret < 0)
@@ -363,7 +356,6 @@ queue_rq_affinity_store(struct gendisk *disk, const char *page, size_t count)
* are accessed individually using atomic test_bit operation. So we
* don't grab any lock while updating these flags.
*/
- memflags = blk_mq_freeze_queue(q);
if (val == 2) {
blk_queue_flag_set(QUEUE_FLAG_SAME_COMP, q);
blk_queue_flag_set(QUEUE_FLAG_SAME_FORCE, q);
@@ -374,7 +366,6 @@ queue_rq_affinity_store(struct gendisk *disk, const char *page, size_t count)
blk_queue_flag_clear(QUEUE_FLAG_SAME_COMP, q);
blk_queue_flag_clear(QUEUE_FLAG_SAME_FORCE, q);
}
- blk_mq_unfreeze_queue(q, memflags);
#endif
return ret;
}
@@ -388,11 +379,9 @@ static ssize_t queue_poll_delay_store(struct gendisk *disk, const char *page,
static ssize_t queue_poll_store(struct gendisk *disk, const char *page,
size_t count)
{
- unsigned int memflags;
ssize_t ret = count;
struct request_queue *q = disk->queue;
- memflags = blk_mq_freeze_queue(q);
if (!(q->limits.features & BLK_FEAT_POLL)) {
ret = -EINVAL;
goto out;
@@ -401,7 +390,6 @@ static ssize_t queue_poll_store(struct gendisk *disk, const char *page,
pr_info_ratelimited("writes to the poll attribute are ignored.\n");
pr_info_ratelimited("please use driver specific parameters instead.\n");
out:
- blk_mq_unfreeze_queue(q, memflags);
return ret;
}
@@ -414,7 +402,7 @@ static ssize_t queue_io_timeout_show(struct gendisk *disk, char *page)
static ssize_t queue_io_timeout_store(struct gendisk *disk, const char *page,
size_t count)
{
- unsigned int val, memflags;
+ unsigned int val;
int err;
struct request_queue *q = disk->queue;
@@ -422,9 +410,7 @@ static ssize_t queue_io_timeout_store(struct gendisk *disk, const char *page,
if (err || val == 0)
return -EINVAL;
- memflags = blk_mq_freeze_queue(q);
blk_queue_rq_timeout(q, msecs_to_jiffies(val));
- blk_mq_unfreeze_queue(q, memflags);
return count;
}
