linux-stable.git/block/blk-sysfs.c, branch linux-6.13.y Linux kernel stable tree block: mark GFP_NOIO around sysfs ->store() 2025-02-17T10:36:16+00:00 Ming Lei tom.leiming@gmail.com 2025-01-13T01:58:33+00:00 2566ce907e5d5db8a039647208e029ce559baa31 commit 7c0be4ead1f8f5f8be0803f347de0de81e3b8e1c upstream. sysfs ->store is called with queue freezed, meantime we have several ->store() callbacks(update_nr_requests, wbt, scheduler) to allocate memory with GFP_KERNEL which may run into direct reclaim code path, then potential deadlock can be caused. Fix the issue by marking NOIO around sysfs ->store() Reported-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: stable@vger.kernel.org Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: John Garry <john.g.garry@oracle.com> Link: https://lore.kernel.org/r/20250113015833.698458-1-ming.lei@redhat.com Link: https://lore.kernel.org/linux-block/Z4RkemI9f6N5zoEF@fedora/T/#mc774c65eeca5c024d29695f9ac6152b87763f305 Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 7c0be4ead1f8f5f8be0803f347de0de81e3b8e1c upstream.

sysfs ->store is called with queue freezed, meantime we have several
->store() callbacks(update_nr_requests, wbt, scheduler) to allocate
memory with GFP_KERNEL which may run into direct reclaim code path,
then potential deadlock can be caused.

Fix the issue by marking NOIO around sysfs ->store()

Reported-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20250113015833.698458-1-ming.lei@redhat.com
Link: https://lore.kernel.org/linux-block/Z4RkemI9f6N5zoEF@fedora/T/#mc774c65eeca5c024d29695f9ac6152b87763f305
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
block: fix queue freeze vs limits lock order in sysfs store methods 2025-02-08T09:00:55+00:00 Christoph Hellwig hch@lst.de 2025-01-10T05:47:14+00:00 8985da5481562e96b95e94ed8e5cc9b6565eb82b [ Upstream commit c99f66e4084a62a2cc401c4704a84328aeddc9ec ] queue_attr_store() always freezes a device queue before calling the attribute store operation. For attributes that control queue limits, the store operation will also lock the queue limits with a call to queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may need to issue commands to a device to obtain limit values from the hardware with the queue limits locked. This creates a potential ABBA deadlock situation if a user attempts to modify a limit (thus freezing the device queue) while the device driver starts a revalidation of the device queue limits. Avoid such deadlock by not freezing the queue before calling the ->store_limit() method in struct queue_sysfs_entry and instead use the queue_limits_commit_update_frozen helper to freeze the queue after taking the limits lock. This also removes taking the sysfs lock for the store_limit method as it doesn't protect anything here, but creates even more nesting. Hopefully it will go away from the actual sysfs methods entirely soon. (commit log adapted from a similar patch from Damien Le Moal) Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store") Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store") Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Link: https://lore.kernel.org/r/20250110054726.1499538-7-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit c99f66e4084a62a2cc401c4704a84328aeddc9ec ]

queue_attr_store() always freezes a device queue before calling the
attribute store operation. For attributes that control queue limits, the
store operation will also lock the queue limits with a call to
queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may
need to issue commands to a device to obtain limit values from the
hardware with the queue limits locked. This creates a potential ABBA
deadlock situation if a user attempts to modify a limit (thus freezing
the device queue) while the device driver starts a revalidation of the
device queue limits.

Avoid such deadlock by not freezing the queue before calling the
->store_limit() method in struct queue_sysfs_entry and instead use the
queue_limits_commit_update_frozen helper to freeze the queue after taking
the limits lock.

This also removes taking the sysfs lock for the store_limit method as
it doesn't protect anything here, but creates even more nesting.
Hopefully it will go away from the actual sysfs methods entirely soon.

(commit log adapted from a similar patch from  Damien Le Moal)

Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store")
Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20250110054726.1499538-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
block: add a store_limit operations for sysfs entries 2025-02-08T09:00:55+00:00 Christoph Hellwig hch@lst.de 2025-01-10T05:47:13+00:00 323148ac214b5dd36c78f2dddc244029e0c64146 [ Upstream commit a16230649ce27f8ac7dd8a5b079d9657aa96de16 ] De-duplicate the code for updating queue limits by adding a store_limit method that allows having common code handle the actual queue limits update. Note that this is a pure refactoring patch and does not address the existing freeze vs limits lock order problem in the refactored code, which will be addressed next. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Reviewed-by: John Garry <john.g.garry@oracle.com> Link: https://lore.kernel.org/r/20250110054726.1499538-6-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> Stable-dep-of: c99f66e4084a ("block: fix queue freeze vs limits lock order in sysfs store methods") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a16230649ce27f8ac7dd8a5b079d9657aa96de16 ]

De-duplicate the code for updating queue limits by adding a store_limit
method that allows having common code handle the actual queue limits
update.

Note that this is a pure refactoring patch and does not address the
existing freeze vs limits lock order problem in the refactored code,
which will be addressed next.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20250110054726.1499538-6-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: c99f66e4084a ("block: fix queue freeze vs limits lock order in sysfs store methods")
Signed-off-by: Sasha Levin <sashal@kernel.org>
block: don't update BLK_FEAT_POLL in __blk_mq_update_nr_hw_queues 2025-02-08T09:00:55+00:00 Christoph Hellwig hch@lst.de 2025-01-10T05:47:12+00:00 9467169f7b619a07ed19106cb5443bbdfd1d3ffc [ Upstream commit d432c817c21a48c3baaa0d28e4d3e74b6aa238a0 ] When __blk_mq_update_nr_hw_queues changes the number of tag sets, it might have to disable poll queues. Currently it does so by adjusting the BLK_FEAT_POLL, which is a bit against the intent of features that describe hardware / driver capabilities, but more importantly causes nasty lock order problems with the broadly held freeze when updating the number of hardware queues and the limits lock. Fix this by leaving BLK_FEAT_POLL alone, and instead check for the number of poll queues in the bio submission and poll handlers. While this adds extra work to the fast path, the variables are in cache lines used by these operations anyway, so it should be cheap enough. Fixes: 8023e144f9d6 ("block: move the poll flag to queue_limits") Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Link: https://lore.kernel.org/r/20250110054726.1499538-5-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit d432c817c21a48c3baaa0d28e4d3e74b6aa238a0 ]

When __blk_mq_update_nr_hw_queues changes the number of tag sets, it
might have to disable poll queues.  Currently it does so by adjusting
the BLK_FEAT_POLL, which is a bit against the intent of features that
describe hardware / driver capabilities, but more importantly causes
nasty lock order problems with the broadly held freeze when updating the
number of hardware queues and the limits lock.  Fix this by leaving
BLK_FEAT_POLL alone, and instead check for the number of poll queues in
the bio submission and poll handlers.  While this adds extra work to the
fast path, the variables are in cache lines used by these operations
anyway, so it should be cheap enough.

Fixes: 8023e144f9d6 ("block: move the poll flag to queue_limits")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250110054726.1499538-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
block: Revert "block: Fix potential deadlock while freezing queue and acquiring sysfs_lock" 2024-12-18T14:25:37+00:00 Ming Lei ming.lei@redhat.com 2024-12-18T10:16:14+00:00 224749be6c23efe7fb8a030854f4fc5d1dd813b3 This reverts commit be26ba96421ab0a8fa2055ccf7db7832a13c44d2. Commit be26ba96421a ("block: Fix potential deadlock while freezing queue and acquiring sysfs_loc") actually reverts commit 22465bbac53c ("blk-mq: move cpuhp callback registering out of q->sysfs_lock"), and causes the original resctrl lockdep warning. So revert it and we need to fix the issue in another way. Cc: Nilay Shroff <nilay@linux.ibm.com> Fixes: be26ba96421a ("block: Fix potential deadlock while freezing queue and acquiring sysfs_loc") Signed-off-by: Ming Lei <ming.lei@redhat.com> Link: https://lore.kernel.org/r/20241218101617.3275704-2-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk> 
This reverts commit be26ba96421ab0a8fa2055ccf7db7832a13c44d2.

Commit be26ba96421a ("block: Fix potential deadlock while freezing queue and
acquiring sysfs_loc") actually reverts commit 22465bbac53c ("blk-mq: move cpuhp
callback registering out of q->sysfs_lock"), and causes the original resctrl
lockdep warning.

So revert it and we need to fix the issue in another way.

Cc: Nilay Shroff <nilay@linux.ibm.com>
Fixes: be26ba96421a ("block: Fix potential deadlock while freezing queue and acquiring sysfs_loc")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241218101617.3275704-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block: Fix potential deadlock while freezing queue and acquiring sysfs_lock 2024-12-13T17:51:58+00:00 Nilay Shroff nilay@linux.ibm.com 2024-12-10T14:41:43+00:00 be26ba96421ab0a8fa2055ccf7db7832a13c44d2 For storing a value to a queue attribute, the queue_attr_store function first freezes the queue (->q_usage_counter(io)) and then acquire ->sysfs_lock. This seems not correct as the usual ordering should be to acquire ->sysfs_lock before freezing the queue. This incorrect ordering causes the following lockdep splat which we are able to reproduce always simply by accessing /sys/kernel/debug file using ls command: [ 57.597146] WARNING: possible circular locking dependency detected [ 57.597154] 6.12.0-10553-gb86545e02e8c #20 Tainted: G W [ 57.597162] ------------------------------------------------------ [ 57.597168] ls/4605 is trying to acquire lock: [ 57.597176] c00000003eb56710 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0x58/0xc0 [ 57.597200] but task is already holding lock: [ 57.597207] c0000018e27c6810 (&sb->s_type->i_mutex_key#3){++++}-{4:4}, at: iterate_dir+0x94/0x1d4 [ 57.597226] which lock already depends on the new lock. [ 57.597233] the existing dependency chain (in reverse order) is: [ 57.597241] -> #5 (&sb->s_type->i_mutex_key#3){++++}-{4:4}: [ 57.597255] down_write+0x6c/0x18c [ 57.597264] start_creating+0xb4/0x24c [ 57.597274] debugfs_create_dir+0x2c/0x1e8 [ 57.597283] blk_register_queue+0xec/0x294 [ 57.597292] add_disk_fwnode+0x2e4/0x548 [ 57.597302] brd_alloc+0x2c8/0x338 [ 57.597309] brd_init+0x100/0x178 [ 57.597317] do_one_initcall+0x88/0x3e4 [ 57.597326] kernel_init_freeable+0x3cc/0x6e0 [ 57.597334] kernel_init+0x34/0x1cc [ 57.597342] ret_from_kernel_user_thread+0x14/0x1c [ 57.597350] -> #4 (&q->debugfs_mutex){+.+.}-{4:4}: [ 57.597362] __mutex_lock+0xfc/0x12a0 [ 57.597370] blk_register_queue+0xd4/0x294 [ 57.597379] add_disk_fwnode+0x2e4/0x548 [ 57.597388] brd_alloc+0x2c8/0x338 [ 57.597395] brd_init+0x100/0x178 [ 57.597402] do_one_initcall+0x88/0x3e4 [ 57.597410] kernel_init_freeable+0x3cc/0x6e0 [ 57.597418] kernel_init+0x34/0x1cc [ 57.597426] ret_from_kernel_user_thread+0x14/0x1c [ 57.597434] -> #3 (&q->sysfs_lock){+.+.}-{4:4}: [ 57.597446] __mutex_lock+0xfc/0x12a0 [ 57.597454] queue_attr_store+0x9c/0x110 [ 57.597462] sysfs_kf_write+0x70/0xb0 [ 57.597471] kernfs_fop_write_iter+0x1b0/0x2ac [ 57.597480] vfs_write+0x3dc/0x6e8 [ 57.597488] ksys_write+0x84/0x140 [ 57.597495] system_call_exception+0x130/0x360 [ 57.597504] system_call_common+0x160/0x2c4 [ 57.597516] -> #2 (&q->q_usage_counter(io)#21){++++}-{0:0}: [ 57.597530] __submit_bio+0x5ec/0x828 [ 57.597538] submit_bio_noacct_nocheck+0x1e4/0x4f0 [ 57.597547] iomap_readahead+0x2a0/0x448 [ 57.597556] xfs_vm_readahead+0x28/0x3c [ 57.597564] read_pages+0x88/0x41c [ 57.597571] page_cache_ra_unbounded+0x1ac/0x2d8 [ 57.597580] filemap_get_pages+0x188/0x984 [ 57.597588] filemap_read+0x13c/0x4bc [ 57.597596] xfs_file_buffered_read+0x88/0x17c [ 57.597605] xfs_file_read_iter+0xac/0x158 [ 57.597614] vfs_read+0x2d4/0x3b4 [ 57.597622] ksys_read+0x84/0x144 [ 57.597629] system_call_exception+0x130/0x360 [ 57.597637] system_call_common+0x160/0x2c4 [ 57.597647] -> #1 (mapping.invalidate_lock#2){++++}-{4:4}: [ 57.597661] down_read+0x6c/0x220 [ 57.597669] filemap_fault+0x870/0x100c [ 57.597677] xfs_filemap_fault+0xc4/0x18c [ 57.597684] __do_fault+0x64/0x164 [ 57.597693] __handle_mm_fault+0x1274/0x1dac [ 57.597702] handle_mm_fault+0x248/0x484 [ 57.597711] ___do_page_fault+0x428/0xc0c [ 57.597719] hash__do_page_fault+0x30/0x68 [ 57.597727] do_hash_fault+0x90/0x35c [ 57.597736] data_access_common_virt+0x210/0x220 [ 57.597745] _copy_from_user+0xf8/0x19c [ 57.597754] sel_write_load+0x178/0xd54 [ 57.597762] vfs_write+0x108/0x6e8 [ 57.597769] ksys_write+0x84/0x140 [ 57.597777] system_call_exception+0x130/0x360 [ 57.597785] system_call_common+0x160/0x2c4 [ 57.597794] -> #0 (&mm->mmap_lock){++++}-{4:4}: [ 57.597806] __lock_acquire+0x17cc/0x2330 [ 57.597814] lock_acquire+0x138/0x400 [ 57.597822] __might_fault+0x7c/0xc0 [ 57.597830] filldir64+0xe8/0x390 [ 57.597839] dcache_readdir+0x80/0x2d4 [ 57.597846] iterate_dir+0xd8/0x1d4 [ 57.597855] sys_getdents64+0x88/0x2d4 [ 57.597864] system_call_exception+0x130/0x360 [ 57.597872] system_call_common+0x160/0x2c4 [ 57.597881] other info that might help us debug this: [ 57.597888] Chain exists of: &mm->mmap_lock --> &q->debugfs_mutex --> &sb->s_type->i_mutex_key#3 [ 57.597905] Possible unsafe locking scenario: [ 57.597911] CPU0 CPU1 [ 57.597917] ---- ---- [ 57.597922] rlock(&sb->s_type->i_mutex_key#3); [ 57.597932] lock(&q->debugfs_mutex); [ 57.597940] lock(&sb->s_type->i_mutex_key#3); [ 57.597950] rlock(&mm->mmap_lock); [ 57.597958] *** DEADLOCK *** [ 57.597965] 2 locks held by ls/4605: [ 57.597971] #0: c0000000137c12f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0xcc/0x154 [ 57.597989] #1: c0000018e27c6810 (&sb->s_type->i_mutex_key#3){++++}-{4:4}, at: iterate_dir+0x94/0x1d4 Prevent the above lockdep warning by acquiring ->sysfs_lock before freezing the queue while storing a queue attribute in queue_attr_store function. Later, we also found[1] another function __blk_mq_update_nr_ hw_queues where we first freeze queue and then acquire the ->sysfs_lock. So we've also updated lock ordering in __blk_mq_update_nr_hw_queues function and ensured that in all code paths we follow the correct lock ordering i.e. acquire ->sysfs_lock before freezing the queue. [1] https://lore.kernel.org/all/CAFj5m9Ke8+EHKQBs_Nk6hqd=LGXtk4mUxZUN5==ZcCjnZSBwHw@mail.gmail.com/ Reported-by: kjain@linux.ibm.com Fixes: af2814149883 ("block: freeze the queue in queue_attr_store") Tested-by: kjain@linux.ibm.com Cc: hch@lst.de Cc: axboe@kernel.dk Cc: ritesh.list@gmail.com Cc: ming.lei@redhat.com Cc: gjoyce@linux.ibm.com Signed-off-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Link: https://lore.kernel.org/r/20241210144222.1066229-1-nilay@linux.ibm.com Signed-off-by: Jens Axboe <axboe@kernel.dk> 
For storing a value to a queue attribute, the queue_attr_store function
first freezes the queue (->q_usage_counter(io)) and then acquire
->sysfs_lock. This seems not correct as the usual ordering should be to
acquire ->sysfs_lock before freezing the queue. This incorrect ordering
causes the following lockdep splat which we are able to reproduce always
simply by accessing /sys/kernel/debug file using ls command:

[   57.597146] WARNING: possible circular locking dependency detected
[   57.597154] 6.12.0-10553-gb86545e02e8c #20 Tainted: G        W
[   57.597162] ------------------------------------------------------
[   57.597168] ls/4605 is trying to acquire lock:
[   57.597176] c00000003eb56710 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0x58/0xc0
[   57.597200]
               but task is already holding lock:
[   57.597207] c0000018e27c6810 (&sb->s_type->i_mutex_key#3){++++}-{4:4}, at: iterate_dir+0x94/0x1d4
[   57.597226]
               which lock already depends on the new lock.

[   57.597233]
               the existing dependency chain (in reverse order) is:
[   57.597241]
               -> #5 (&sb->s_type->i_mutex_key#3){++++}-{4:4}:
[   57.597255]        down_write+0x6c/0x18c
[   57.597264]        start_creating+0xb4/0x24c
[   57.597274]        debugfs_create_dir+0x2c/0x1e8
[   57.597283]        blk_register_queue+0xec/0x294
[   57.597292]        add_disk_fwnode+0x2e4/0x548
[   57.597302]        brd_alloc+0x2c8/0x338
[   57.597309]        brd_init+0x100/0x178
[   57.597317]        do_one_initcall+0x88/0x3e4
[   57.597326]        kernel_init_freeable+0x3cc/0x6e0
[   57.597334]        kernel_init+0x34/0x1cc
[   57.597342]        ret_from_kernel_user_thread+0x14/0x1c
[   57.597350]
               -> #4 (&q->debugfs_mutex){+.+.}-{4:4}:
[   57.597362]        __mutex_lock+0xfc/0x12a0
[   57.597370]        blk_register_queue+0xd4/0x294
[   57.597379]        add_disk_fwnode+0x2e4/0x548
[   57.597388]        brd_alloc+0x2c8/0x338
[   57.597395]        brd_init+0x100/0x178
[   57.597402]        do_one_initcall+0x88/0x3e4
[   57.597410]        kernel_init_freeable+0x3cc/0x6e0
[   57.597418]        kernel_init+0x34/0x1cc
[   57.597426]        ret_from_kernel_user_thread+0x14/0x1c
[   57.597434]
               -> #3 (&q->sysfs_lock){+.+.}-{4:4}:
[   57.597446]        __mutex_lock+0xfc/0x12a0
[   57.597454]        queue_attr_store+0x9c/0x110
[   57.597462]        sysfs_kf_write+0x70/0xb0
[   57.597471]        kernfs_fop_write_iter+0x1b0/0x2ac
[   57.597480]        vfs_write+0x3dc/0x6e8
[   57.597488]        ksys_write+0x84/0x140
[   57.597495]        system_call_exception+0x130/0x360
[   57.597504]        system_call_common+0x160/0x2c4
[   57.597516]
               -> #2 (&q->q_usage_counter(io)#21){++++}-{0:0}:
[   57.597530]        __submit_bio+0x5ec/0x828
[   57.597538]        submit_bio_noacct_nocheck+0x1e4/0x4f0
[   57.597547]        iomap_readahead+0x2a0/0x448
[   57.597556]        xfs_vm_readahead+0x28/0x3c
[   57.597564]        read_pages+0x88/0x41c
[   57.597571]        page_cache_ra_unbounded+0x1ac/0x2d8
[   57.597580]        filemap_get_pages+0x188/0x984
[   57.597588]        filemap_read+0x13c/0x4bc
[   57.597596]        xfs_file_buffered_read+0x88/0x17c
[   57.597605]        xfs_file_read_iter+0xac/0x158
[   57.597614]        vfs_read+0x2d4/0x3b4
[   57.597622]        ksys_read+0x84/0x144
[   57.597629]        system_call_exception+0x130/0x360
[   57.597637]        system_call_common+0x160/0x2c4
[   57.597647]
               -> #1 (mapping.invalidate_lock#2){++++}-{4:4}:
[   57.597661]        down_read+0x6c/0x220
[   57.597669]        filemap_fault+0x870/0x100c
[   57.597677]        xfs_filemap_fault+0xc4/0x18c
[   57.597684]        __do_fault+0x64/0x164
[   57.597693]        __handle_mm_fault+0x1274/0x1dac
[   57.597702]        handle_mm_fault+0x248/0x484
[   57.597711]        ___do_page_fault+0x428/0xc0c
[   57.597719]        hash__do_page_fault+0x30/0x68
[   57.597727]        do_hash_fault+0x90/0x35c
[   57.597736]        data_access_common_virt+0x210/0x220
[   57.597745]        _copy_from_user+0xf8/0x19c
[   57.597754]        sel_write_load+0x178/0xd54
[   57.597762]        vfs_write+0x108/0x6e8
[   57.597769]        ksys_write+0x84/0x140
[   57.597777]        system_call_exception+0x130/0x360
[   57.597785]        system_call_common+0x160/0x2c4
[   57.597794]
               -> #0 (&mm->mmap_lock){++++}-{4:4}:
[   57.597806]        __lock_acquire+0x17cc/0x2330
[   57.597814]        lock_acquire+0x138/0x400
[   57.597822]        __might_fault+0x7c/0xc0
[   57.597830]        filldir64+0xe8/0x390
[   57.597839]        dcache_readdir+0x80/0x2d4
[   57.597846]        iterate_dir+0xd8/0x1d4
[   57.597855]        sys_getdents64+0x88/0x2d4
[   57.597864]        system_call_exception+0x130/0x360
[   57.597872]        system_call_common+0x160/0x2c4
[   57.597881]
               other info that might help us debug this:

[   57.597888] Chain exists of:
                 &mm->mmap_lock --> &q->debugfs_mutex --> &sb->s_type->i_mutex_key#3

[   57.597905]  Possible unsafe locking scenario:

[   57.597911]        CPU0                    CPU1
[   57.597917]        ----                    ----
[   57.597922]   rlock(&sb->s_type->i_mutex_key#3);
[   57.597932]                                lock(&q->debugfs_mutex);
[   57.597940]                                lock(&sb->s_type->i_mutex_key#3);
[   57.597950]   rlock(&mm->mmap_lock);
[   57.597958]
                *** DEADLOCK ***

[   57.597965] 2 locks held by ls/4605:
[   57.597971]  #0: c0000000137c12f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0xcc/0x154
[   57.597989]  #1: c0000018e27c6810 (&sb->s_type->i_mutex_key#3){++++}-{4:4}, at: iterate_dir+0x94/0x1d4

Prevent the above lockdep warning by acquiring ->sysfs_lock before
freezing the queue while storing a queue attribute in queue_attr_store
function. Later, we also found[1] another function __blk_mq_update_nr_
hw_queues where we first freeze queue and then acquire the ->sysfs_lock.
So we've also updated lock ordering in __blk_mq_update_nr_hw_queues
function and ensured that in all code paths we follow the correct lock
ordering i.e. acquire ->sysfs_lock before freezing the queue.

[1] https://lore.kernel.org/all/CAFj5m9Ke8+EHKQBs_Nk6hqd=LGXtk4mUxZUN5==ZcCjnZSBwHw@mail.gmail.com/

Reported-by: kjain@linux.ibm.com
Fixes: af2814149883 ("block: freeze the queue in queue_attr_store")
Tested-by: kjain@linux.ibm.com
Cc: hch@lst.de
Cc: axboe@kernel.dk
Cc: ritesh.list@gmail.com
Cc: ming.lei@redhat.com
Cc: gjoyce@linux.ibm.com
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241210144222.1066229-1-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block: Fix queue_iostats_passthrough_show() 2024-12-13T15:09:43+00:00 Bart Van Assche bvanassche@acm.org 2024-12-12T21:29:41+00:00 a6fe7b70513fbf11ffa5e85f7b6ba444497a5a3d Make queue_iostats_passthrough_show() report 0/1 in sysfs instead of 0/4. This patch fixes the following sparse warning: block/blk-sysfs.c:266:31: warning: incorrect type in argument 1 (different base types) block/blk-sysfs.c:266:31: expected unsigned long var block/blk-sysfs.c:266:31: got restricted blk_flags_t Cc: Keith Busch <kbusch@kernel.org> Cc: Christoph Hellwig <hch@lst.de> Fixes: 110234da18ab ("block: enable passthrough command statistics") Signed-off-by: Bart Van Assche <bvanassche@acm.org> Link: https://lore.kernel.org/r/20241212212941.1268662-4-bvanassche@acm.org Signed-off-by: Jens Axboe <axboe@kernel.dk> 
Make queue_iostats_passthrough_show() report 0/1 in sysfs instead of 0/4.

This patch fixes the following sparse warning:
block/blk-sysfs.c:266:31: warning: incorrect type in argument 1 (different base types)
block/blk-sysfs.c:266:31:    expected unsigned long var
block/blk-sysfs.c:266:31:    got restricted blk_flags_t

Cc: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Fixes: 110234da18ab ("block: enable passthrough command statistics")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20241212212941.1268662-4-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block: fix uaf for flush rq while iterating tags 2024-11-19T01:31:57+00:00 Yu Kuai yukuai3@huawei.com 2024-11-04T11:00:05+00:00 3802f73bd80766d70f319658f334754164075bc3 blk_mq_clear_flush_rq_mapping() is not called during scsi probe, by checking blk_queue_init_done(). However, QUEUE_FLAG_INIT_DONE is cleared in del_gendisk by commit aec89dc5d421 ("block: keep q_usage_counter in atomic mode after del_gendisk"), hence for disk like scsi, following blk_mq_destroy_queue() will not clear flush rq from tags->rqs[] as well, cause following uaf that is found by our syzkaller for v6.6: ================================================================== BUG: KASAN: slab-use-after-free in blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261 Read of size 4 at addr ffff88811c969c20 by task kworker/1:2H/224909 CPU: 1 PID: 224909 Comm: kworker/1:2H Not tainted 6.6.0-ga836a5060850 #32 Workqueue: kblockd blk_mq_timeout_work Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106 print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364 print_report+0x3e/0x70 mm/kasan/report.c:475 kasan_report+0xb8/0xf0 mm/kasan/report.c:588 blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261 bt_iter block/blk-mq-tag.c:288 [inline] __sbitmap_for_each_set include/linux/sbitmap.h:295 [inline] sbitmap_for_each_set include/linux/sbitmap.h:316 [inline] bt_for_each+0x455/0x790 block/blk-mq-tag.c:325 blk_mq_queue_tag_busy_iter+0x320/0x740 block/blk-mq-tag.c:534 blk_mq_timeout_work+0x1a3/0x7b0 block/blk-mq.c:1673 process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631 process_scheduled_works kernel/workqueue.c:2704 [inline] worker_thread+0x804/0xe40 kernel/workqueue.c:2785 kthread+0x346/0x450 kernel/kthread.c:388 ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293 Allocated by task 942: kasan_save_stack+0x22/0x50 mm/kasan/common.c:45 kasan_set_track+0x25/0x30 mm/kasan/common.c:52 ____kasan_kmalloc mm/kasan/common.c:374 [inline] __kasan_kmalloc mm/kasan/common.c:383 [inline] __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:380 kasan_kmalloc include/linux/kasan.h:198 [inline] __do_kmalloc_node mm/slab_common.c:1007 [inline] __kmalloc_node+0x69/0x170 mm/slab_common.c:1014 kmalloc_node include/linux/slab.h:620 [inline] kzalloc_node include/linux/slab.h:732 [inline] blk_alloc_flush_queue+0x144/0x2f0 block/blk-flush.c:499 blk_mq_alloc_hctx+0x601/0x940 block/blk-mq.c:3788 blk_mq_alloc_and_init_hctx+0x27f/0x330 block/blk-mq.c:4261 blk_mq_realloc_hw_ctxs+0x488/0x5e0 block/blk-mq.c:4294 blk_mq_init_allocated_queue+0x188/0x860 block/blk-mq.c:4350 blk_mq_init_queue_data block/blk-mq.c:4166 [inline] blk_mq_init_queue+0x8d/0x100 block/blk-mq.c:4176 scsi_alloc_sdev+0x843/0xd50 drivers/scsi/scsi_scan.c:335 scsi_probe_and_add_lun+0x77c/0xde0 drivers/scsi/scsi_scan.c:1189 __scsi_scan_target+0x1fc/0x5a0 drivers/scsi/scsi_scan.c:1727 scsi_scan_channel drivers/scsi/scsi_scan.c:1815 [inline] scsi_scan_channel+0x14b/0x1e0 drivers/scsi/scsi_scan.c:1791 scsi_scan_host_selected+0x2fe/0x400 drivers/scsi/scsi_scan.c:1844 scsi_scan+0x3a0/0x3f0 drivers/scsi/scsi_sysfs.c:151 store_scan+0x2a/0x60 drivers/scsi/scsi_sysfs.c:191 dev_attr_store+0x5c/0x90 drivers/base/core.c:2388 sysfs_kf_write+0x11c/0x170 fs/sysfs/file.c:136 kernfs_fop_write_iter+0x3fc/0x610 fs/kernfs/file.c:338 call_write_iter include/linux/fs.h:2083 [inline] new_sync_write+0x1b4/0x2d0 fs/read_write.c:493 vfs_write+0x76c/0xb00 fs/read_write.c:586 ksys_write+0x127/0x250 fs/read_write.c:639 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81 entry_SYSCALL_64_after_hwframe+0x78/0xe2 Freed by task 244687: kasan_save_stack+0x22/0x50 mm/kasan/common.c:45 kasan_set_track+0x25/0x30 mm/kasan/common.c:52 kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522 ____kasan_slab_free mm/kasan/common.c:236 [inline] __kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244 kasan_slab_free include/linux/kasan.h:164 [inline] slab_free_hook mm/slub.c:1815 [inline] slab_free_freelist_hook mm/slub.c:1841 [inline] slab_free mm/slub.c:3807 [inline] __kmem_cache_free+0xe4/0x520 mm/slub.c:3820 blk_free_flush_queue+0x40/0x60 block/blk-flush.c:520 blk_mq_hw_sysfs_release+0x4a/0x170 block/blk-mq-sysfs.c:37 kobject_cleanup+0x136/0x410 lib/kobject.c:689 kobject_release lib/kobject.c:720 [inline] kref_put include/linux/kref.h:65 [inline] kobject_put+0x119/0x140 lib/kobject.c:737 blk_mq_release+0x24f/0x3f0 block/blk-mq.c:4144 blk_free_queue block/blk-core.c:298 [inline] blk_put_queue+0xe2/0x180 block/blk-core.c:314 blkg_free_workfn+0x376/0x6e0 block/blk-cgroup.c:144 process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631 process_scheduled_works kernel/workqueue.c:2704 [inline] worker_thread+0x804/0xe40 kernel/workqueue.c:2785 kthread+0x346/0x450 kernel/kthread.c:388 ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293 Other than blk_mq_clear_flush_rq_mapping(), the flag is only used in blk_register_queue() from initialization path, hence it's safe not to clear the flag in del_gendisk. And since QUEUE_FLAG_REGISTERED already make sure that queue should only be registered once, there is no need to test the flag as well. Fixes: 6cfeadbff3f8 ("blk-mq: don't clear flush_rq from tags->rqs[]") Depends-on: commit aec89dc5d421 ("block: keep q_usage_counter in atomic mode after del_gendisk") Signed-off-by: Yu Kuai <yukuai3@huawei.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Link: https://lore.kernel.org/r/20241104110005.1412161-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe <axboe@kernel.dk> 
blk_mq_clear_flush_rq_mapping() is not called during scsi probe, by
checking blk_queue_init_done(). However, QUEUE_FLAG_INIT_DONE is cleared
in del_gendisk by commit aec89dc5d421 ("block: keep q_usage_counter in
atomic mode after del_gendisk"), hence for disk like scsi, following
blk_mq_destroy_queue() will not clear flush rq from tags->rqs[] as well,
cause following uaf that is found by our syzkaller for v6.6:

==================================================================
BUG: KASAN: slab-use-after-free in blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261
Read of size 4 at addr ffff88811c969c20 by task kworker/1:2H/224909

CPU: 1 PID: 224909 Comm: kworker/1:2H Not tainted 6.6.0-ga836a5060850 #32
Workqueue: kblockd blk_mq_timeout_work
Call Trace:

__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
print_report+0x3e/0x70 mm/kasan/report.c:475
kasan_report+0xb8/0xf0 mm/kasan/report.c:588
blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261
bt_iter block/blk-mq-tag.c:288 [inline]
__sbitmap_for_each_set include/linux/sbitmap.h:295 [inline]
sbitmap_for_each_set include/linux/sbitmap.h:316 [inline]
bt_for_each+0x455/0x790 block/blk-mq-tag.c:325
blk_mq_queue_tag_busy_iter+0x320/0x740 block/blk-mq-tag.c:534
blk_mq_timeout_work+0x1a3/0x7b0 block/blk-mq.c:1673
process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631
process_scheduled_works kernel/workqueue.c:2704 [inline]
worker_thread+0x804/0xe40 kernel/workqueue.c:2785
kthread+0x346/0x450 kernel/kthread.c:388
ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293

Allocated by task 942:
kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc mm/kasan/common.c:383 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:380
kasan_kmalloc include/linux/kasan.h:198 [inline]
__do_kmalloc_node mm/slab_common.c:1007 [inline]
__kmalloc_node+0x69/0x170 mm/slab_common.c:1014
kmalloc_node include/linux/slab.h:620 [inline]
kzalloc_node include/linux/slab.h:732 [inline]
blk_alloc_flush_queue+0x144/0x2f0 block/blk-flush.c:499
blk_mq_alloc_hctx+0x601/0x940 block/blk-mq.c:3788
blk_mq_alloc_and_init_hctx+0x27f/0x330 block/blk-mq.c:4261
blk_mq_realloc_hw_ctxs+0x488/0x5e0 block/blk-mq.c:4294
blk_mq_init_allocated_queue+0x188/0x860 block/blk-mq.c:4350
blk_mq_init_queue_data block/blk-mq.c:4166 [inline]
blk_mq_init_queue+0x8d/0x100 block/blk-mq.c:4176
scsi_alloc_sdev+0x843/0xd50 drivers/scsi/scsi_scan.c:335
scsi_probe_and_add_lun+0x77c/0xde0 drivers/scsi/scsi_scan.c:1189
__scsi_scan_target+0x1fc/0x5a0 drivers/scsi/scsi_scan.c:1727
scsi_scan_channel drivers/scsi/scsi_scan.c:1815 [inline]
scsi_scan_channel+0x14b/0x1e0 drivers/scsi/scsi_scan.c:1791
scsi_scan_host_selected+0x2fe/0x400 drivers/scsi/scsi_scan.c:1844
scsi_scan+0x3a0/0x3f0 drivers/scsi/scsi_sysfs.c:151
store_scan+0x2a/0x60 drivers/scsi/scsi_sysfs.c:191
dev_attr_store+0x5c/0x90 drivers/base/core.c:2388
sysfs_kf_write+0x11c/0x170 fs/sysfs/file.c:136
kernfs_fop_write_iter+0x3fc/0x610 fs/kernfs/file.c:338
call_write_iter include/linux/fs.h:2083 [inline]
new_sync_write+0x1b4/0x2d0 fs/read_write.c:493
vfs_write+0x76c/0xb00 fs/read_write.c:586
ksys_write+0x127/0x250 fs/read_write.c:639
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x78/0xe2

Freed by task 244687:
kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
__kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1815 [inline]
slab_free_freelist_hook mm/slub.c:1841 [inline]
slab_free mm/slub.c:3807 [inline]
__kmem_cache_free+0xe4/0x520 mm/slub.c:3820
blk_free_flush_queue+0x40/0x60 block/blk-flush.c:520
blk_mq_hw_sysfs_release+0x4a/0x170 block/blk-mq-sysfs.c:37
kobject_cleanup+0x136/0x410 lib/kobject.c:689
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x119/0x140 lib/kobject.c:737
blk_mq_release+0x24f/0x3f0 block/blk-mq.c:4144
blk_free_queue block/blk-core.c:298 [inline]
blk_put_queue+0xe2/0x180 block/blk-core.c:314
blkg_free_workfn+0x376/0x6e0 block/blk-cgroup.c:144
process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631
process_scheduled_works kernel/workqueue.c:2704 [inline]
worker_thread+0x804/0xe40 kernel/workqueue.c:2785
kthread+0x346/0x450 kernel/kthread.c:388
ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293

Other than blk_mq_clear_flush_rq_mapping(), the flag is only used in
blk_register_queue() from initialization path, hence it's safe not to
clear the flag in del_gendisk. And since QUEUE_FLAG_REGISTERED already
make sure that queue should only be registered once, there is no need
to test the flag as well.

Fixes: 6cfeadbff3f8 ("blk-mq: don't clear flush_rq from tags->rqs[]")
Depends-on: commit aec89dc5d421 ("block: keep q_usage_counter in atomic mode after del_gendisk")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241104110005.1412161-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block: pre-calculate max_zone_append_sectors 2024-11-11T16:20:36+00:00 Christoph Hellwig hch@lst.de 2024-11-08T15:46:51+00:00 559218d43ec9dde3d2847c7aa127e88d6ab1c9ed max_zone_append_sectors differs from all other queue limits in that the final value used is not stored in the queue_limits but needs to be obtained using queue_limits_max_zone_append_sectors helper. This not only adds (tiny) extra overhead to the I/O path, but also can be easily forgotten in file system code. Add a new max_hw_zone_append_sectors value to queue_limits which is set by the driver, and calculate max_zone_append_sectors from that and the other inputs in blk_validate_zoned_limits, similar to how max_sectors is calculated to fix this. Signed-off-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20241104073955.112324-3-hch@lst.de Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Link: https://lore.kernel.org/r/20241108154657.845768-2-hch@lst.de Signed-off-by: Jens Axboe <axboe@kernel.dk> 
max_zone_append_sectors differs from all other queue limits in that the
final value used is not stored in the queue_limits but needs to be
obtained using queue_limits_max_zone_append_sectors helper.  This not
only adds (tiny) extra overhead to the I/O path, but also can be easily
forgotten in file system code.

Add a new max_hw_zone_append_sectors value to queue_limits which is
set by the driver, and calculate max_zone_append_sectors from that and
the other inputs in blk_validate_zoned_limits, similar to how
max_sectors is calculated to fix this.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241104073955.112324-3-hch@lst.de
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20241108154657.845768-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block: Replace sprintf() with sysfs_emit() 2024-11-07T22:30:30+00:00 zhangguopeng zhangguopeng@kylinos.cn 2024-11-07T10:42:58+00:00 8e71afb94d6ed59055b67dadbc423c70104f21a9 Per Documentation/filesystems/sysfs.rst, show() should only use sysfs_emit() or sysfs_emit_at() when formatting the value to be returned to user space. No functional change intended. Signed-off-by: zhangguopeng <zhangguopeng@kylinos.cn> Suggested-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20241107104258.29742-1-zhangguopeng@kylinos.cn Signed-off-by: Jens Axboe <axboe@kernel.dk> 
Per Documentation/filesystems/sysfs.rst, show() should only use
sysfs_emit() or sysfs_emit_at() when formatting the value to be
returned to user space.

No functional change intended.

Signed-off-by: zhangguopeng <zhangguopeng@kylinos.cn>
Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241107104258.29742-1-zhangguopeng@kylinos.cn
Signed-off-by: Jens Axboe <axboe@kernel.dk>