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 <hch@lst.de>
Link: https://lore.kernel.org/r/20250131120352.1315351-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 <hch@lst.de>
Link: https://lore.kernel.org/r/20250106083531.799976-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20241008050841.104602-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit e4eb37cc0f ("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: e4eb37cc0f ("block: Remove elevator required features")
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/20241011155615.3361143-1-leitao@debian.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 e3accac1a9 ("block: Fix elv_iosched_local_module handling of "none" scheduler")
Fixes: 734e1a8603 ("block: Prevent deadlocks when switching elevators")
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/20241011170122.3880087-1-leitao@debian.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 <surajsonawane0215@gmail.com>
Link: https://lore.kernel.org/r/20241007111416.13814-1-surajsonawane0215@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit 734e1a8603 ("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 734e1a8603, 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 <shinichiro.kawasaki@wdc.com>
Fixes: 734e1a8603 ("block: Prevent deadlocks when switching elevators")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240917133231.134806-1-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit af28141498 ("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 <rjones@redhat.com>
Reported-by: Jiri Jaburek <jjaburek@redhat.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219166
Fixes: af28141498 ("block: freeze the queue in queue_attr_store")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Link: https://lore.kernel.org/r/20240908000704.414538-1-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Tested-by: Dennis Maisenbacher <dennis.maisenbacher@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240408014128.205141-23-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Chuck reported [1] an IO hang problem on NFS exports that reside on SATA
devices and bisected to commit 615939a2ae ("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 <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202308172100.8ce4b853-oliver.sang@intel.com
Fixes: 615939a2ae ("blk-mq: defer to the normal submission path for post-flush requests")
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
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 <axboe@kernel.dk>
The kobject embedded into the request_queue is used for the queue
directory in sysfs, but that is a child of the gendisks directory and is
intimately tied to it. Move this kobject to the gendisk and use a
refcount_t in the request_queue for the actual request_queue refcounting
that is completely unrelated to the device model.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221114042637.1009333-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
