kernel/linux.git/block/blk-sysfs.c, branch v7.1-rc5

block: make queue_sysfs_entry instances const

2026-03-18T01:29:16+00:00

The queue_sysfs_entry structures are never modified, mark them as const. Signed-off-by: Thomas Weißschuh Reviewed-by: John Garry Link: https://patch.msgid.link/20260316-b4-sysfs-const-attr-block-v1-1-a35d73b986b0@weissschuh.net Signed-off-by: Jens Axboe

block: default to QD=1 writes for blk-mq rotational zoned devices

2026-03-09T20:30:00+00:00

For blk-mq rotational zoned block devices (e.g. SMR HDDs), default to having zone write plugging limit write operations to a maximum queue depth of 1 for all zones. This significantly reduce write seek overhead and improves SMR HDD write throughput. For remotely connected disks with a very high network latency this features might not be useful. However, remotely connected zoned devices are rare at the moment, and we cannot know the round trip latency to pick a good default for network attached devices. System administrators can however disable this feature in that case. For BIO based (non blk-mq) rotational zoned block devices, the device driver (e.g. a DM target driver) can directly set an appropriate default. Signed-off-by: Damien Le Moal Reviewed-by: Hannes Reinecke Reviewed-by: Christoph Hellwig Reviewed-by: Bart Van Assche Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

block: allow submitting all zone writes from a single context

2026-03-09T20:30:00+00:00

In order to maintain sequential write patterns per zone with zoned block devices, zone write plugging issues only a single write BIO per zone at any time. This works well but has the side effect that when large sequential write streams are issued by the user and these streams cross zone boundaries, the device ends up receiving a discontiguous set of write commands for different zones. The same also happens when a user writes simultaneously at high queue depth multiple zones: the device does not see all sequential writes per zone and receives discontiguous writes to different zones. While this does not affect the performance of solid state zoned block devices, when using an SMR HDD, this pattern change from sequential writes to discontiguous writes to different zones significantly increases head seek which results in degraded write throughput. In order to reduce this seek overhead for rotational media devices, introduce a per disk zone write plugs kernel thread to issue all write BIOs to zones. This single zone write issuing context is enabled for any zoned block device that has a request queue flagged with the new QUEUE_ZONED_QD1_WRITES flag. The flag QUEUE_ZONED_QD1_WRITES is visible as the sysfs queue attribute zoned_qd1_writes for zoned devices. For regular block devices, this attribute is not visible. For zoned block devices, a user can override the default value set to force the global write maximum queue depth of 1 for a zoned block device, or clear this attribute to fallback to the default behavior of zone write plugging which limits writes to QD=1 per sequential zone. Writing to a zoned block device flagged with QUEUE_ZONED_QD1_WRITES is implemented using a list of zone write plugs that have a non-empty BIO list. Listed zone write plugs are processed by the disk zone write plugs worker kthread in FIFO order, and all BIOs of a zone write plug are all processed before switching to the next listed zone write plug. A newly submitted BIO for a non-FULL zone write plug that is not yet listed causes the addition of the zone write plug at the end of the disk list of zone write plugs. Since the write BIOs queued in a zone write plug BIO list are necessarilly sequential, for rotational media, using the single zone write plugs kthread to issue all BIOs maintains a sequential write pattern and thus reduces seek overhead and improves write throughput. This processing essentially result in always writing to HDDs at QD=1, which is not an issue for HDDs operating with write caching enabled. Performance with write cache disabled is also not degraded thanks to the efficient write handling of modern SMR HDDs. A disk list of zone write plugs is defined using the new struct gendisk zone_wplugs_list, and accesses to this list is protected using the zone_wplugs_list_lock spinlock. The per disk kthread (zone_wplugs_worker) code is implemented by the function disk_zone_wplugs_worker(). A reference on listed zone write plugs is always held until all BIOs of the zone write plug are processed by the worker kthread. BIO issuing at QD=1 is driven using a completion structure (zone_wplugs_worker_bio_done) and calls to blk_io_wait(). With this change, performance when sequentially writing the zones of a 30 TB SMR SATA HDD connected to an AHCI adapter changes as follows (1MiB direct I/Os, results in MB/s unit): +--------------------+ | Write BW (MB/s) | +------------------+----------+---------+ | Sequential write | Baseline | Patched | | Queue Depth | 6.19-rc8 | | +------------------+----------+---------+ | 1 | 244 | 245 | | 2 | 244 | 245 | | 4 | 245 | 245 | | 8 | 242 | 245 | | 16 | 222 | 246 | | 32 | 211 | 245 | | 64 | 193 | 244 | | 128 | 112 | 246 | +------------------+----------+---------+ With the current code (baseline), as the sequential write stream crosses a zone boundary, higher queue depth creates a gap between the last IO to the previous zone and the first IOs to the following zones, causing head seeks and degrading performance. Using the disk zone write plugs worker thread, this pattern disappears and the maximum throughput of the drive is maintained, leading to over 100% improvements in throughput for high queue depth write. Using 16 fio jobs all writing to randomly chosen zones at QD=32 with 1 MiB direct IOs, write throughput also increases significantly. +--------------------+ | Write BW (MB/s) | +------------------+----------+---------+ | Random write | Baseline | Patched | | Number of zones | 6.19-rc7 | | +------------------+----------+---------+ | 1 | 191 | 192 | | 2 | 101 | 128 | | 4 | 115 | 123 | | 8 | 90 | 120 | | 16 | 64 | 115 | | 32 | 58 | 105 | | 64 | 56 | 101 | | 128 | 55 | 99 | +------------------+----------+---------+ Tests using XFS shows that buffered write speed with 8 jobs writing files increases by 12% to 35% depending on the workload. +--------------------+ | Write BW (MB/s) | +------------------+----------+---------+ | Workload | Baseline | Patched | | | 6.19-rc7 | | +------------------+----------+---------+ | 256MiB file size | 212 | 238 | +------------------+----------+---------+ | 4MiB .. 128 MiB | 213 | 243 | | random file size | | | +------------------+----------+---------+ | 2MiB .. 8 MiB | 179 | 242 | | random file size | | | +------------------+----------+---------+ Performance gains are even more significant when using an HBA that limits the maximum size of commands to a small value, e.g. HBAs controlled with the mpi3mr driver limit commands to a maximum of 1 MiB. In such case, the write throughput gains are over 40%. +--------------------+ | Write BW (MB/s) | +------------------+----------+---------+ | Workload | Baseline | Patched | | | 6.19-rc7 | | +------------------+----------+---------+ | 256MiB file size | 175 | 245 | +------------------+----------+---------+ | 4MiB .. 128 MiB | 174 | 244 | | random file size | | | +------------------+----------+---------+ | 2MiB .. 8 MiB | 171 | 243 | | random file size | | | +------------------+----------+---------+ Signed-off-by: Damien Le Moal Reviewed-by: Christoph Hellwig Reviewed-by: Bart Van Assche Reviewed-by: Johannes Thumshirn Signed-off-by: Jens Axboe

block: use trylock to avoid lockdep circular dependency in sysfs

2026-03-05T11:01:42+00:00

Use trylock instead of blocking lock acquisition for update_nr_hwq_lock in queue_requests_store() and elv_iosched_store() to avoid circular lock dependency with kernfs active reference during concurrent disk deletion: update_nr_hwq_lock -> kn->active (via del_gendisk -> kobject_del) kn->active -> update_nr_hwq_lock (via sysfs write path) Return -EBUSY when the lock is not immediately available. Reported-and-tested-by: Yi Zhang Closes: https://lore.kernel.org/linux-block/CAHj4cs-em-4acsHabMdT=jJhXkCzjnprD-aQH1OgrZo4nTnmMw@mail.gmail.com/ Fixes: 626ff4f8ebcb ("blk-mq: convert to serialize updating nr_requests with update_nr_hwq_lock") Signed-off-by: Ming Lei Tested-by: Yi Zhang Signed-off-by: Jens Axboe

blk-mq: use NOIO context to prevent deadlock during debugfs creation

2026-02-16T17:47:25+00:00

Creating debugfs entries can trigger fs reclaim, which can enter back into the block layer request_queue. This can cause deadlock if the queue is frozen. Previously, a WARN_ON_ONCE check was used in debugfs_create_files() to detect this condition, but it was racy since the queue can be frozen from another context at any time. Introduce blk_debugfs_lock()/blk_debugfs_unlock() helpers that combine the debugfs_mutex with memalloc_noio_save()/restore() to prevent fs reclaim from triggering block I/O. Also add blk_debugfs_lock_nomemsave() and blk_debugfs_unlock_nomemrestore() variants for callers that don't need NOIO protection (e.g., debugfs removal or read-only operations). Replace all raw debugfs_mutex lock/unlock pairs with these helpers, using the _nomemsave/_nomemrestore variants where appropriate. Reported-by: Yi Zhang Closes: https://lore.kernel.org/all/CAHj4cs9gNKEYAPagD9JADfO5UH+OiCr4P7OO2wjpfOYeM-RV=A@mail.gmail.com/ Reported-by: Shinichiro Kawasaki Closes: https://lore.kernel.org/all/aYWQR7CtYdk3K39g@shinmob/ Suggested-by: Christoph Hellwig Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe

blk-mq: add a new queue sysfs attribute async_depth

2026-02-03T14:45:36+00:00

Add a new field async_depth to request_queue and related APIs, this is currently not used, following patches will convert elevators to use this instead of internal async_depth. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe

blk-wbt: factor out a helper wbt_set_lat()

2026-02-02T14:05:19+00:00

To move implementation details inside blk-wbt.c, prepare to fix possible deadlock to call wbt_init() while queue is frozen in the next patch. Reviewed-by: Ming Lei Reviewed-by: Nilay Shroff Signed-off-by: Yu Kuai Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

block: fix race between wbt_enable_default and IO submission

2025-12-12T19:51:11+00:00

When wbt_enable_default() is moved out of queue freezing in elevator_change(), it can cause the wbt inflight counter to become negative (-1), leading to hung tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter is in an inconsistent state. The issue occurs because wbt_enable_default() could race with IO submission, allowing the counter to be decremented before proper initialization. This manifests as: rq_wait[0]: inflight: -1 has_waiters: True rwb_enabled() checks the state, which can be updated exactly between wbt_wait() (rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter will become negative. And results in hung task warnings like: task:kworker/u24:39 state:D stack:0 pid:14767 Call Trace: rq_qos_wait+0xb4/0x150 wbt_wait+0xa9/0x100 __rq_qos_throttle+0x24/0x40 blk_mq_submit_bio+0x672/0x7b0 ... Fix this by: 1. Splitting wbt_enable_default() into: - __wbt_enable_default(): Returns true if wbt_init() should be called - wbt_enable_default(): Wrapper for existing callers (no init) - wbt_init_enable_default(): New function that checks and inits WBT 2. Using wbt_init_enable_default() in blk_register_queue() to ensure proper initialization during queue registration 3. Move wbt_init() out of wbt_enable_default() which is only for enabling disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the original lock warning can be avoided. 4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling code since it's no longer needed This ensures WBT is properly initialized before any IO can be submitted, preventing the counter from going negative. Cc: Nilay Shroff Cc: Yu Kuai Cc: Guangwu Zhang Fixes: 78c271344b6f ("block: move wbt_enable_default() out of queue freezing from sched ->exit()") Signed-off-by: Ming Lei Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe

block: Remove queue freezing from several sysfs store callbacks

2025-11-18T22:00:11+00:00

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. Add the __data_racy annotation to request_queue.rq_timeout to suppress KCSAN data race reports about the rq_timeout reads. This patch may cause a small delay in applying the new settings. For all the attributes affected by this patch, I/O will complete correctly whether the old or the new value of the attribute is used. 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 if this patch is not applied: task:multipathd Call Trace: __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:(udev-worker) Call Trace: __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 Cc: Christoph Hellwig Cc: Ming Lei Cc: Nilay Shroff Cc: Martin Wilck Cc: Benjamin Marzinski Cc: stable@vger.kernel.org Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") Signed-off-by: Bart Van Assche Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe

blk-mq: fix potential deadlock while nr_requests grown

2025-09-10T11:25:56+00:00

Allocate and free sched_tags while queue is freezed can deadlock[1], this is a long term problem, hence allocate memory before freezing queue and free memory after queue is unfreezed. [1] https://lore.kernel.org/all/0659ea8d-a463-47c8-9180-43c719e106eb@linux.ibm.com/ Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs") Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe