linux-stable.git/block/elevator.h, branch v6.15

block: introduce a dedicated lock for protecting queue elevator updates

2025-03-10T13:30:18+00:00

A queue's elevator can be updated either when modifying nr_hw_queues
or through the sysfs scheduler attribute. Currently, elevator switching/
updating is protected using q->sysfs_lock, but this has led to lockdep
splats[1] due to inconsistent lock ordering between q->sysfs_lock and
the freeze-lock in multiple block layer call sites.

As the scope of q->sysfs_lock is not well-defined, its (mis)use has
resulted in numerous lockdep warnings. To address this, introduce a new
q->elevator_lock, dedicated specifically for protecting elevator
switches/updates. And we'd now use this new q->elevator_lock instead of
q->sysfs_lock for protecting elevator switches/updates.

While at it, make elv_iosched_load_module() a static function, as it is
only called from elv_iosched_store(). Also, remove redundant parameters
from elv_iosched_load_module() function signature.

[1] https://lore.kernel.org/all/67637e70.050a0220.3157ee.000c.GAE@google.com/

Reviewed-by: Christoph Hellwig 
Reviewed-by: Hannes Reinecke 
Reviewed-by: Ming Lei 
Signed-off-by: Nilay Shroff 
Link: https://lore.kernel.org/r/20250304102551.2533767-5-nilay@linux.ibm.com
Signed-off-by: Jens Axboe

elevator: Enable const sysfs attributes

2025-01-02T20:20:29+00:00

The elevator core does not need to modify the sysfs attributes added by
the elevators. Reflect this in the types, so the attributes can be moved
into read-only memory.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20250102-sysfs-const-attr-elevator-v1-1-9837d2058c60@weissschuh.net
Signed-off-by: Jens Axboe

block: return void from the queue_sysfs_entry load_module method

2024-10-22T14:16:22+00:00

Requesting a module either succeeds or does nothing, return an error from
this method does not make sense.

Also move the load_module after the store method in the struct
declaration to keep the important show and store methods together.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Damien Le Moal 
Reviewed-by: Andreas Hindborg 
Link: https://lore.kernel.org/r/20241008050841.104602-1-hch@lst.de
Signed-off-by: Jens Axboe

block: Prevent deadlocks when switching elevators

2024-09-10T19:43:42+00:00

Commit af2814149883 ("block: freeze the queue in queue_attr_store")
changed queue_attr_store() to always freeze a sysfs attribute queue
before calling the attribute store() method, to ensure that no IOs are
in-flight when an attribute value is being updated.

However, this change created a potential deadlock situation for the
scheduler queue attribute as changing the queue elevator with
elv_iosched_store() can result in a call to request_module() if the user
requested module is not already registered. If the file of the requested
module is stored on the block device of the frozen queue, a deadlock
will happen as the read operations triggered by request_module() will
wait for the queue freeze to end.

Solve this issue by introducing the load_module method in struct
queue_sysfs_entry, and to calling this method function in
queue_attr_store() before freezing the attribute queue.
The macro definition QUEUE_RW_LOAD_MODULE_ENTRY() is added to define a
queue sysfs attribute that needs loading a module.

The definition of the scheduler atrribute is changed to using
QUEUE_RW_LOAD_MODULE_ENTRY(), with the function
elv_iosched_load_module() defined as the load_module method.
elv_iosched_store() can then be simplified to remove the call to
request_module().

Reported-by: Richard W.M. Jones 
Reported-by: Jiri Jaburek 
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166
Fixes: af2814149883 ("block: freeze the queue in queue_attr_store")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal 
Tested-by: Richard W.M. Jones 
Link: https://lore.kernel.org/r/20240908000704.414538-1-dlemoal@kernel.org
Signed-off-by: Jens Axboe

block: pass a gendisk to the queue_sysfs_entry methods

2024-06-28T21:06:16+00:00

The kobject for the queue entries is embedded into a struct gendisk.
Pass it to the sysfs methods instead of the request_queue derived from
it.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20240627111407.476276-4-hch@lst.de
Signed-off-by: Jens Axboe

block: Remove elevator required features

2024-04-17T14:44:03+00:00

The only elevator feature ever implemented is ELEVATOR_F_ZBD_SEQ_WRITE
for signaling that a scheduler implements zone write locking to tightly
control the dispatching order of write operations to zoned block
devices. With the removal of zone write locking support in mq-deadline
and the reliance of all block device drivers on the block layer zone
write plugging to control ordering of write operations to zones, the
elevator feature ELEVATOR_F_ZBD_SEQ_WRITE is completely unused.
Remove it, and also remove the now unused code for filtering the
possible schedulers for a block device based on required features.

Signed-off-by: Damien Le Moal 
Reviewed-by: Hannes Reinecke 
Reviewed-by: Christoph Hellwig 
Reviewed-by: Bart Van Assche 
Tested-by: Hans Holmberg 
Tested-by: Dennis Maisenbacher 
Reviewed-by: Martin K. Petersen 
Link: https://lore.kernel.org/r/20240408014128.205141-23-dlemoal@kernel.org
Signed-off-by: Jens Axboe

blk-mq: pass a flags argument to elevator_type->insert_requests

2023-04-13T12:52:30+00:00

Instead of passing a bool at_head, pass down the full flags from the
blk_mq_insert_request interface.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Bart Van Assche 
Reviewed-by: Damien Le Moal 
Link: https://lore.kernel.org/r/20230413064057.707578-20-hch@lst.de
Signed-off-by: Jens Axboe

block: add proper helpers for elevator_type module refcount management

2022-10-24T00:59:17+00:00

Make sure we have helpers for all relevant module refcount operations on
the elevator_type in elevator.h, and use them.  Move the call to the get
helper in blk_mq_elv_switch_none a bit so that it is obvious with a less
verbose comment.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20221020064819.1469928-2-hch@lst.de
Signed-off-by: Jens Axboe

blk-wbt: don't enable throttling if default elevator is bfq

2022-10-24T00:59:17+00:00

Commit b5dc5d4d1f4f ("block,bfq: Disable writeback throttling") tries to
disable wbt for bfq, it's done by calling wbt_disable_default() in
bfq_init_queue(). However, wbt is still enabled if default elevator is
bfq:

device_add_disk
 elevator_init_mq
  bfq_init_queue
   wbt_disable_default -> done nothing

 blk_register_queue
  wbt_enable_default -> wbt is enabled

Fix the problem by adding a new flag ELEVATOR_FLAG_DISBALE_WBT, bfq
will set the flag in bfq_init_queue, and following wbt_enable_default()
won't enable wbt while the flag is set.

Signed-off-by: Yu Kuai 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20221019121518.3865235-7-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe

elevator: add new field flags in struct elevator_queue

2022-10-24T00:59:17+00:00

There are only one flag to indicate that elevator is registered currently,
prepare to add a flag to disable wbt if default elevator is bfq.

Signed-off-by: Yu Kuai 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20221019121518.3865235-6-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe