linux-stable.git/block/elevator.c, 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

block: move q->sysfs_lock and queue-freeze under show/store method

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

In preparation to further simplify and group sysfs attributes which
don't require locking or require some form of locking other than q->
limits_lock, move acquire/release of q->sysfs_lock and queue freeze/
unfreeze under each attributes' respective show/store method.

While we are at it, also remove ->load_module() as it's used to load
the module before queue is freezed. Now as we moved queue-freeze under
->store(), we could load module directly from the attributes' store
method before we actually start freezing the queue. Currently, the
->load_module() is only used by "scheduler" attribute, so we now load
the relevant elevator module before we start freezing the queue in
elv_iosched_store().

Reviewed-by: Christoph Hellwig 
Reviewed-by: Hannes Reinecke 
Reviewed-by: Ming Lei 
Signed-off-by: Nilay Shroff 
Link: https://lore.kernel.org/r/20250304102551.2533767-3-nilay@linux.ibm.com
Signed-off-by: Jens Axboe

block: force noio scope in blk_mq_freeze_queue

2025-01-31T14:20:08+00:00

When block drivers or the core block code perform allocations with a
frozen queue, this could try to recurse into the block device to
reclaim memory and deadlock.  Thus all allocations done by a process
that froze a queue need to be done without __GFP_IO and __GFP_FS.
Instead of tying to track all of them down, force a noio scope as
part of freezing the queue.

Note that nvme is a bit of a mess here due to the non-owner freezes,
and they will be addressed separately.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20250131120352.1315351-2-hch@lst.de
Signed-off-by: Jens Axboe

block: remove BLK_MQ_F_NO_SCHED

2025-01-06T14:37:41+00:00

The only queues that really can't support a scheduler are those that
do not have a gendisk associated with them, and thus can't be used for
non-passthrough commands.  In addition to those null_blk can optionally
set the flag, which is a bad odd.  Replace the null_blk usage with
BLK_MQ_F_NO_SCHED_BY_DEFAULT to keep the expected semantics and then
remove BLK_MQ_F_NO_SCHED as the non-disk queues never call into
elevator_init_mq or blk_register_queue which adds the sysfs attributes.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20250106083531.799976-4-hch@lst.de
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: don't verify queue freeze manually in elevator_init_mq()

2024-12-23T15:17:22+00:00

Now blk_freeze_queue_start() can track disk state automatically, and
it isn't necessary to verify queue freeze manually in elevator_init_mq()
any more.

Signed-off-by: Ming Lei 
Link: https://lore.kernel.org/r/20241127135133.3952153-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe

block: track disk DEAD state automatically for modeling queue freeze lockdep

2024-12-23T15:17:22+00:00

Now we only verify the outmost freeze & unfreeze in current context in case
that !q->mq_freeze_depth, so it is reliable to save disk DEAD state when
we want to lock the freeze queue since the state is one per-task variable
now.

Doing this way can kill lots of false positive when freeze queue is
called before adding disk[1].

[1] https://lore.kernel.org/linux-block/6741f6b2.050a0220.1cc393.0017.GAE@google.com/

Signed-off-by: Ming Lei 
Link: https://lore.kernel.org/r/20241127135133.3952153-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe

block: don't verify IO lock for freeze/unfreeze in elevator_init_mq()

2024-11-07T23:27:22+00:00

elevator_init_mq() is only called at the entry of add_disk_fwnode() when
disk IO isn't allowed yet.

So not verify io lock(q->io_lockdep_map) for freeze & unfreeze in
elevator_init_mq().

Reported-by: Marek Szyprowski 
Reported-by: Lai Yi 
Fixes: f1be1788a32e ("block: model freeze & enter queue as lock for supporting lockdep")
Signed-off-by: Ming Lei 
Link: https://lore.kernel.org/r/20241031133723.303835-5-ming.lei@redhat.com
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

elevator: Remove argument from elevator_find_get

2024-10-11T17:11:09+00:00

Commit e4eb37cc0f3ed ("block: Remove elevator required features")
removed the usage of `struct request_queue` from elevator_find_get(),
but didn't removed the argument.

Remove the "struct request_queue *q" argument from elevator_find_get()
given it is useless.

Fixes: e4eb37cc0f3e ("block: Remove elevator required features")
Signed-off-by: Breno Leitao 
Link: https://lore.kernel.org/r/20241011155615.3361143-1-leitao@debian.org
Signed-off-by: Jens Axboe