linux-stable.git/block/elevator.c, branch v6.12

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

elevator: do not request_module if elevator exists

2024-10-11T17:10:52+00:00

Whenever an I/O elevator is changed, the system attempts to load a
module for the new elevator. This occurs regardless of whether the
elevator is already loaded or built directly into the kernel. This
behavior introduces unnecessary overhead and potential issues.

This makes the operation slower, and more error-prone. For instance,
making the problem fixed by [1] visible for users that doesn't even rely
on modules being available through modules.

Do not try to load the ioscheduler if it is already visible.

This change brings two main benefits: it improves the performance of
elevator changes, and it reduces the likelihood of errors occurring
during this process.

[1] Commit e3accac1a976 ("block: Fix elv_iosched_local_module handling of "none" scheduler")

Fixes: 734e1a860312 ("block: Prevent deadlocks when switching elevators")
Signed-off-by: Breno Leitao 
Link: https://lore.kernel.org/r/20241011170122.3880087-1-leitao@debian.org
Signed-off-by: Jens Axboe

block: Fix elevator_get_default() checking for NULL q->tag_set

2024-10-07T20:24:36+00:00

elevator_get_default() and elv_support_iosched() both check for whether
or not q->tag_set is non-NULL, however it's not possible for them to be
NULL. This messes up some static checkers, as the checking of tag_set
isn't consistent.

Remove the checks, which both simplifies the logic and avoids checker
errors.

Signed-off-by: SurajSonawane2415 
Link: https://lore.kernel.org/r/20241007111416.13814-1-surajsonawane0215@gmail.com
Signed-off-by: Jens Axboe

block: Fix elv_iosched_local_module handling of "none" scheduler

2024-09-17T14:34:00+00:00

Commit 734e1a860312 ("block: Prevent deadlocks when switching
elevators") introduced the function elv_iosched_load_module() to allow
loading an elevator module outside of elv_iosched_store() with the
target device queue not frozen, to avoid deadlocks. However, the "none"
scheduler does not have a module and as a result,
elv_iosched_load_module() always returns an error when trying to switch
to this valid scheduler.

Fix this by ignoring the return value of the request_module() call
done by elv_iosched_load_module(). This restores the behavior before
commit 734e1a860312, which was to ignore the request_module() result and
instead rely on elevator_change() to handle the "none" scheduler case.

Reported-by: Shin'ichiro Kawasaki 
Fixes: 734e1a860312 ("block: Prevent deadlocks when switching elevators")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20240917133231.134806-1-dlemoal@kernel.org
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: release scheduler resource when request completes

2023-08-19T13:47:17+00:00

Chuck reported [1] an IO hang problem on NFS exports that reside on SATA
devices and bisected to commit 615939a2ae73 ("blk-mq: defer to the normal
submission path for post-flush requests").

We analysed the IO hang problem, found there are two postflush requests
waiting for each other.

The first postflush request completed the REQ_FSEQ_DATA sequence, so go to
the REQ_FSEQ_POSTFLUSH sequence and added in the flush pending list, but
failed to blk_kick_flush() because of the second postflush request which
is inflight waiting in scheduler queue.

The second postflush waiting in scheduler queue can't be dispatched because
the first postflush hasn't released scheduler resource even though it has
completed by itself.

Fix it by releasing scheduler resource when the first postflush request
completed, so the second postflush can be dispatched and completed, then
make blk_kick_flush() succeed.

While at it, remove the check for e->ops.finish_request, as all
schedulers set that. Reaffirm this requirement by adding a WARN_ON_ONCE()
at scheduler registration time, just like we do for insert_requests and
dispatch_request.

[1] https://lore.kernel.org/all/7A57C7AE-A51A-4254-888B-FE15CA21F9E9@oracle.com/

Link: https://lore.kernel.org/linux-block/20230819031206.2744005-1-chengming.zhou@linux.dev/
Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-lkp/202308172100.8ce4b853-oliver.sang@intel.com
Fixes: 615939a2ae73 ("blk-mq: defer to the normal submission path for post-flush requests")
Reported-by: Chuck Lever 
Signed-off-by: Chengming Zhou 
Tested-by: Chuck Lever 
Link: https://lore.kernel.org/r/20230813152325.3017343-1-chengming.zhou@linux.dev
[axboe: folded in incremental fix and added tags]
Signed-off-by: Jens Axboe

block: Replace all non-returning strlcpy with strscpy

2023-06-01T15:13:31+00:00

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
No return values were used, so direct replacement is safe.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh 
Reviewed-by: Kees Cook 
Link: https://lore.kernel.org/r/20230530155608.272266-1-azeemshaikh38@gmail.com
Signed-off-by: Jens Axboe

block: make kobj_type structures constant

2023-02-09T16:38:16+00:00

Since commit ee6d3dd4ed48 ("driver core: make kobj_type constant.")
the driver core allows the usage of const struct kobj_type.

Take advantage of this to constify the structure definitions to prevent
modification at runtime.

Signed-off-by: Thomas Weißschuh 
Link: https://lore.kernel.org/r/20230208-kobj_type-block-v1-1-0b3eafd7d983@weissschuh.net
Signed-off-by: Jens Axboe