diff options
author | Damien Le Moal <damien.lemoal@wdc.com> | 2020-11-06 14:01:41 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2020-11-06 19:36:42 +0300 |
commit | e1777d099728a76a8f8090f89649aac961e7e530 (patch) | |
tree | 27dac735a263de3ca72c7b8cdbf2c2179fd23f7e /drivers/block | |
parent | 7ae7a8de054253024624abebd86eb25c5bdaf1c8 (diff) | |
download | linux-e1777d099728a76a8f8090f89649aac961e7e530.tar.xz |
null_blk: Fix scheduling in atomic with zoned mode
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.
Fixes: aa1c09cb65e2 ("null_blk: Fix locking in zoned mode")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block')
-rw-r--r-- | drivers/block/null_blk.h | 2 | ||||
-rw-r--r-- | 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); |