block: introduce a dedicated lock for protecting queue elevator updates

A queue's elevator can be updated either when modifying nr_hw_queues
or through the sysfs scheduler attribute. Currently, elev

block: introduce a dedicated lock for protecting queue elevator updates

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/[email protected]/

Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Signed-off-by: Nilay Shroff <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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elevator: Enable const sysfs attributes

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-onl

elevator: Enable const sysfs attributes

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 <[email protected]>
Link: https://lore.kernel.org/r/20250102-sysfs-const-attr-elevator-v1-1-9837d2058c60@weissschuh.net
Signed-off-by: Jens Axboe <[email protected]>

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block: return void from the queue_sysfs_entry load_module method

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

Also move the load_module

block: return void from the queue_sysfs_entry load_module method

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 <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: Prevent deadlocks when switching elevators

Commit af2814149883 ("block: freeze the queue in queue_attr_store")
changed queue_attr_store() to always freeze a sysfs attribute queue
before calli

block: Prevent deadlocks when switching elevators

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 <[email protected]>
Reported-by: Jiri Jaburek <[email protected]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166
Fixes: af2814149883 ("block: freeze the queue in queue_attr_store")
Cc: [email protected]
Signed-off-by: Damien Le Moal <[email protected]>
Tested-by: Richard W.M. Jones <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: pass a gendisk to the queue_sysfs_entry methods

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.

block: pass a gendisk to the queue_sysfs_entry methods

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 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: Remove elevator required features

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 di

block: Remove elevator required features

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 <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Tested-by: Hans Holmberg <[email protected]>
Tested-by: Dennis Maisenbacher <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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

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

Signed-off-by: Christoph Hellwi

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

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

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: add proper helpers for elevator_type module refcount management

Make sure we have helpers for all relevant module refcount operations on
the elevator_type in elevator.h, and use them. Move t

block: add proper helpers for elevator_type module refcount management

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 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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

Commit b5dc5d4d1f4f ("block,bfq: Disable writeback throttling") tries to
disable wbt for bfq, it's done by calling wbt_disable_default() i

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

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 <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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elevator: add new field flags in struct elevator_queue

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.

Si

elevator: add new field flags in struct elevator_queue

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 <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: Use the new blk_opf_t type

Use the new blk_opf_t type for arguments and variables that represent
request flags or a bitwise combination of a request operation and
request flags. Rename the fu

block: Use the new blk_opf_t type

Use the new blk_opf_t type for arguments and variables that represent
request flags or a bitwise combination of a request operation and
request flags. Rename the function arguments and also a structure member
that hold a request operation and flags from 'rw' into 'opf'.

This patch does not change any functionality.

Cc: Christoph Hellwig <[email protected]>
Cc: Ming Lei <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Damien Le Moal <[email protected]>
Cc: Johannes Thumshirn <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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block: move elevator.h to block/

Except for the features passed to blk_queue_required_elevator_features,
elevator.h is only needed internally to the block layer. Move the
ELEVATOR_F_* definitions t

block: move elevator.h to block/

Except for the features passed to blk_queue_required_elevator_features,
elevator.h is only needed internally to the block layer. Move the
ELEVATOR_F_* definitions to blkdev.h, and the move elevator.h to
block/, dropping all the spurious includes outside of that.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

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