Commit aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") changed
zone locking to using the potentially sleeping wait_on_bit_io()
function. This is acceptable when memory backing is enabled as the
device queue is in that case marked as blocking, but this triggers a
scheduling while in atomic context with memory backing disabled.
Fix this by relying solely on the device zone spinlock for zone
information protection without temporarily releasing this lock around
null_process_cmd() execution in null_zone_write(). This is OK to do
since when memory backing is disabled, command processing does not
block and the memory backing lock nullb->lock is unused. This solution
avoids the overhead of having to mark a zoned null_blk device queue as
blocking when memory backing is unused.
This patch also adds comments to the zone locking code to explain the
unusual locking scheme.
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Fixes: aa1c09cb65e2 ("null_blk: Fix locking in zoned mode")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
drivers/block/null_blk.h | 2 +-
drivers/block/null_blk_zoned.c | 47 ++++++++++++++++++++++------------
2 files changed, 32 insertions(+), 17 deletions(-)
diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
index cfd00ad40355..c24d9b5ad81a 100644
--- a/drivers/block/null_blk.h
+++ b/drivers/block/null_blk.h
@@ -47,7 +47,7 @@ struct nullb_device {
unsigned int nr_zones_closed;
struct blk_zone *zones;
sector_t zone_size_sects;
- spinlock_t zone_dev_lock;
+ spinlock_t zone_lock;
unsigned long *zone_locks;
unsigned long size; /* device size in MB */
diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
index 8775acbb4f8f..beb34b4f76b0 100644
--- a/drivers/block/null_blk_zoned.c
+++ b/drivers/block/null_blk_zoned.c
@@ -46,11 +46,20 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
if (!dev->zones)
return -ENOMEM;
- spin_lock_init(&dev->zone_dev_lock);
- dev->zone_locks = bitmap_zalloc(dev->nr_zones, GFP_KERNEL);
- if (!dev->zone_locks) {
- kvfree(dev->zones);
- return -ENOMEM;
+ /*
+ * With memory backing, the zone_lock spinlock needs to be temporarily
+ * released to avoid scheduling in atomic context. To guarantee zone
+ * information protection, use a bitmap to lock zones with
+ * wait_on_bit_lock_io(). Sleeping on the lock is OK as memory backing
+ * implies that the queue is marked with BLK_MQ_F_BLOCKING.
+ */
+ spin_lock_init(&dev->zone_lock);
+ if (dev->memory_backed) {
+ dev->zone_locks = bitmap_zalloc(dev->nr_zones, GFP_KERNEL);
+ if (!dev->zone_locks) {
+ kvfree(dev->zones);
+ return -ENOMEM;
+ }
}
if (dev->zone_nr_conv >= dev->nr_zones) {
@@ -137,12 +146,17 @@ void null_free_zoned_dev(struct nullb_device *dev)
static inline void null_lock_zone(struct nullb_device *dev, unsigned int zno)
{
- wait_on_bit_lock_io(dev->zone_locks, zno, TASK_UNINTERRUPTIBLE);
+ if (dev->memory_backed)
+ wait_on_bit_lock_io(dev->zone_locks, zno, TASK_UNINTERRUPTIBLE);
+ spin_lock_irq(&dev->zone_lock);
}
static inline void null_unlock_zone(struct nullb_device *dev, unsigned int zno)
{
- clear_and_wake_up_bit(zno, dev->zone_locks);
+ spin_unlock_irq(&dev->zone_lock);
+
+ if (dev->memory_backed)
+ clear_and_wake_up_bit(zno, dev->zone_locks);
}
int null_report_zones(struct gendisk *disk, sector_t sector,
@@ -322,7 +336,6 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
return null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors);
null_lock_zone(dev, zno);
- spin_lock(&dev->zone_dev_lock);
switch (zone->cond) {
case BLK_ZONE_COND_FULL:
@@ -375,9 +388,17 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
if (zone->cond != BLK_ZONE_COND_EXP_OPEN)
zone->cond = BLK_ZONE_COND_IMP_OPEN;
- spin_unlock(&dev->zone_dev_lock);
+ /*
+ * Memory backing allocation may sleep: release the zone_lock spinlock
+ * to avoid scheduling in atomic context. Zone operation atomicity is
+ * still guaranteed through the zone_locks bitmap.
+ */
+ if (dev->memory_backed)
+ spin_unlock_irq(&dev->zone_lock);
ret = null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors);
- spin_lock(&dev->zone_dev_lock);
+ if (dev->memory_backed)
+ spin_lock_irq(&dev->zone_lock);
+
if (ret != BLK_STS_OK)
goto unlock;
@@ -392,7 +413,6 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
ret = BLK_STS_OK;
unlock:
- spin_unlock(&dev->zone_dev_lock);
null_unlock_zone(dev, zno);
return ret;
@@ -516,9 +536,7 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
null_lock_zone(dev, i);
zone = &dev->zones[i];
if (zone->cond != BLK_ZONE_COND_EMPTY) {
- spin_lock(&dev->zone_dev_lock);
null_reset_zone(dev, zone);
- spin_unlock(&dev->zone_dev_lock);
trace_nullb_zone_op(cmd, i, zone->cond);
}
null_unlock_zone(dev, i);
@@ -530,7 +548,6 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
zone = &dev->zones[zone_no];
null_lock_zone(dev, zone_no);
- spin_lock(&dev->zone_dev_lock);
switch (op) {
case REQ_OP_ZONE_RESET:
@@ -550,8 +567,6 @@ static blk_status_t null_zone_mgmt(struct nullb_cmd *cmd, enum req_opf op,
break;
}
- spin_unlock(&dev->zone_dev_lock);
-
if (ret == BLK_STS_OK)
trace_nullb_zone_op(cmd, zone_no, zone->cond);
--
2.26.2
