[ Upstream commit 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 22465bbac53c821319089016f268a2437de9b00a ]
Registering and unregistering cpuhp callback requires global cpu hotplug lock,
which is used everywhere. Meantime q->sysfs_lock is used in block layer
almost everywhere.
It is easy to trigger lockdep warning[1] by connecting the two locks.
Fix the warning by moving blk-mq's cpuhp callback registering out of
q->sysfs_lock. Add one dedicated global lock for covering registering &
unregistering hctx's cpuhp, and it is safe to do so because hctx is
guaranteed to be live if our request_queue is live.
[1] https://lore.kernel.org/lkml/Z04pz3AlvI4o0Mr8@agluck-desk3/
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Newman <peternewman@google.com>
Cc: Babu Moger <babu.moger@amd.com>
Reported-by: Luck Tony <tony.luck@intel.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20241206111611.978870-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: be26ba96421a ("block: Fix potential deadlock while freezing queue and acquiring sysfs_lock")
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 57e420c84f9ab55ba4c5e2ae9c5f6c8e1ea834d2 ]
After a recent change to clamp() and its variants [1] that increases the
coverage of the check that high is greater than low because it can be
done through inlining, certain build configurations (such as s390
defconfig) fail to build with clang with:
block/blk-iocost.c:1101:11: error: call to '__compiletime_assert_557' declared with 'error' attribute: clamp() low limit 1 greater than high limit active
1101 | inuse = clamp_t(u32, inuse, 1, active);
| ^
include/linux/minmax.h:218:36: note: expanded from macro 'clamp_t'
218 | #define clamp_t(type, val, lo, hi) __careful_clamp(type, val, lo, hi)
| ^
include/linux/minmax.h:195:2: note: expanded from macro '__careful_clamp'
195 | __clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_))
| ^
include/linux/minmax.h:188:2: note: expanded from macro '__clamp_once'
188 | BUILD_BUG_ON_MSG(statically_true(ulo > uhi), \
| ^
__propagate_weights() is called with an active value of zero in
ioc_check_iocgs(), which results in the high value being less than the
low value, which is undefined because the value returned depends on the
order of the comparisons.
The purpose of this expression is to ensure inuse is not more than
active and at least 1. This could be written more simply with a ternary
expression that uses min(inuse, active) as the condition so that the
value of that condition can be used if it is not zero and one if it is.
Do this conversion to resolve the error and add a comment to deter
people from turning this back into clamp().
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Link: https://lore.kernel.org/r/34d53778977747f19cce2abb287bb3e6@AcuMS.aculab.com/ [1]
Suggested-by: David Laight <david.laight@aculab.com>
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/llvm/CA+G9fYsD7mw13wredcZn0L-KBA3yeoVSTuxnss-AEWMN3ha0cA@mail.gmail.com/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412120322.3GfVe3vF-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 790eb09e59709a1ffc1c64fe4aae2789120851b0 ]
Call bdev_offset_from_zone_start() instead of open-coding it.
Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Signed-off-by: LongPing Wei <weilongping@oppo.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20241107020439.1644577-1-weilongping@oppo.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
commit 5eb3317aa5a2ffe4574ab1a12cf9bc9447ca26c0 upstream.
There are currently any issuer of REQ_OP_ZONE_RESET and
REQ_OP_ZONE_FINISH operations that set REQ_NOWAIT. However, as we cannot
handle this flag correctly due to the potential request allocation
failure that may happen in blk_mq_submit_bio() after blk_zone_plug_bio()
has handled the zone write plug write pointer updates for the targeted
zones, modify blk_zone_wplug_handle_reset_or_finish() to warn if this
flag is set and ignore it.
Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20241209122357.47838-3-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit fe0418eb9bd69a19a948b297c8de815e05f3cde1 upstream.
Zone write plugging for handling writes to zones of a zoned block
device always execute a zone report whenever a write BIO to a zone
fails. The intent of this is to ensure that the tracking of a zone write
pointer is always correct to ensure that the alignment to a zone write
pointer of write BIOs can be checked on submission and that we can
always correctly emulate zone append operations using regular write
BIOs.
However, this error recovery scheme introduces a potential deadlock if a
device queue freeze is initiated while BIOs are still plugged in a zone
write plug and one of these write operation fails. In such case, the
disk zone write plug error recovery work is scheduled and executes a
report zone. This in turn can result in a request allocation in the
underlying driver to issue the report zones command to the device. But
with the device queue freeze already started, this allocation will
block, preventing the report zone execution and the continuation of the
processing of the plugged BIOs. As plugged BIOs hold a queue usage
reference, the queue freeze itself will never complete, resulting in a
deadlock.
Avoid this problem by completely removing from the zone write plugging
code the use of report zones operations after a failed write operation,
instead relying on the device user to either execute a report zones,
reset the zone, finish the zone, or give up writing to the device (which
is a fairly common pattern for file systems which degrade to read-only
after write failures). This is not an unreasonnable requirement as all
well-behaved applications, FSes and device mapper already use report
zones to recover from write errors whenever possible by comparing the
current position of a zone write pointer with what their assumption
about the position is.
The changes to remove the automatic error recovery are as follows:
- Completely remove the error recovery work and its associated
resources (zone write plug list head, disk error list, and disk
zone_wplugs_work work struct). This also removes the functions
disk_zone_wplug_set_error() and disk_zone_wplug_clear_error().
- Change the BLK_ZONE_WPLUG_ERROR zone write plug flag into
BLK_ZONE_WPLUG_NEED_WP_UPDATE. This new flag is set for a zone write
plug whenever a write opration targetting the zone of the zone write
plug fails. This flag indicates that the zone write pointer offset is
not reliable and that it must be updated when the next report zone,
reset zone, finish zone or disk revalidation is executed.
- Modify blk_zone_write_plug_bio_endio() to set the
BLK_ZONE_WPLUG_NEED_WP_UPDATE flag for the target zone of a failed
write BIO.
- Modify the function disk_zone_wplug_set_wp_offset() to clear this
new flag, thus implementing recovery of a correct write pointer
offset with the reset (all) zone and finish zone operations.
- Modify blkdev_report_zones() to always use the disk_report_zones_cb()
callback so that disk_zone_wplug_sync_wp_offset() can be called for
any zone marked with the BLK_ZONE_WPLUG_NEED_WP_UPDATE flag.
This implements recovery of a correct write pointer offset for zone
write plugs marked with BLK_ZONE_WPLUG_NEED_WP_UPDATE and within
the range of the report zones operation executed by the user.
- Modify blk_revalidate_seq_zone() to call
disk_zone_wplug_sync_wp_offset() for all sequential write required
zones when a zoned block device is revalidated, thus always resolving
any inconsistency between the write pointer offset of zone write
plugs and the actual write pointer position of sequential zones.
Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20241209122357.47838-5-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit b76b840fd93374240b59825f1ab8e2f5c9907acb upstream.
The zone reclaim processing of the dm-zoned device mapper uses
blkdev_issue_zeroout() to align the write pointer of a zone being used
for reclaiming another zone, to write the valid data blocks from the
zone being reclaimed at the same position relative to the zone start in
the reclaim target zone.
The first call to blkdev_issue_zeroout() will try to use hardware
offload using a REQ_OP_WRITE_ZEROES operation if the device reports a
non-zero max_write_zeroes_sectors queue limit. If this operation fails
because of the lack of hardware support, blkdev_issue_zeroout() falls
back to using a regular write operation with the zero-page as buffer.
Currently, such REQ_OP_WRITE_ZEROES failure is automatically handled by
the block layer zone write plugging code which will execute a report
zones operation to ensure that the write pointer of the target zone of
the failed operation has not changed and to "rewind" the zone write
pointer offset of the target zone as it was advanced when the write zero
operation was submitted. So the REQ_OP_WRITE_ZEROES failure does not
cause any issue and blkdev_issue_zeroout() works as expected.
However, since the automatic recovery of zone write pointers by the zone
write plugging code can potentially cause deadlocks with queue freeze
operations, a different recovery must be implemented in preparation for
the removal of zone write plugging report zones based recovery.
Do this by introducing the new function blk_zone_issue_zeroout(). This
function first calls blkdev_issue_zeroout() with the flag
BLKDEV_ZERO_NOFALLBACK to intercept failures on the first execution
which attempt to use the device hardware offload with the
REQ_OP_WRITE_ZEROES operation. If this attempt fails, a report zone
operation is issued to restore the zone write pointer offset of the
target zone to the correct position and blkdev_issue_zeroout() is called
again without the BLKDEV_ZERO_NOFALLBACK flag. The report zones
operation performing this recovery is implemented using the helper
function disk_zone_sync_wp_offset() which calls the gendisk report_zones
file operation with the callback disk_report_zones_cb(). This callback
updates the target write pointer offset of the target zone using the new
function disk_zone_wplug_sync_wp_offset().
dmz_reclaim_align_wp() is modified to change its call to
blkdev_issue_zeroout() to a call to blk_zone_issue_zeroout() without any
other change needed as the two functions are functionnally equivalent.
Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20241209122357.47838-4-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit cae005670887cb07ceafc25bb32e221e56286488 upstream.
For zoned block devices, a write BIO issued to a zone that has no
on-going writes will be prepared for execution and allowed to execute
immediately by blk_zone_wplug_handle_write() (called from
blk_zone_plug_bio()). However, if this BIO specifies REQ_NOWAIT, the
allocation of a request for its execution in blk_mq_submit_bio() may
fail after blk_zone_plug_bio() completed, marking the target zone of the
BIO as plugged. When this BIO is retried later on, it will be blocked as
the zone write plug of the target zone is in a plugged state without any
on-going write operation (completion of write operations trigger
unplugging of the next write BIOs for a zone). This leads to a BIO that
is stuck in a zone write plug and never completes, which results in
various issues such as hung tasks.
Avoid this problem by always executing REQ_NOWAIT write BIOs using the
BIO work of a zone write plug. This ensure that we never block the BIO
issuer and can thus safely ignore the REQ_NOWAIT flag when executing the
BIO from the zone write plug BIO work.
Since such BIO may be the first write BIO issued to a zone with no
on-going write, modify disk_zone_wplug_add_bio() to schedule the zone
write plug BIO work if the write plug is not already marked with the
BLK_ZONE_WPLUG_PLUGGED flag. This scheduling is otherwise not necessary
as the completion of the on-going write for the zone will schedule the
execution of the next plugged BIOs.
blk_zone_wplug_handle_write() is also fixed to better handle zone write
plug allocation failures for REQ_NOWAIT BIOs by failing a write BIO
using bio_wouldblock_error() instead of bio_io_error().
Reported-by: Bart Van Assche <bvanassche@acm.org>
Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20241209122357.47838-2-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 4122fef16b172f7c1838fcf74340268c86ed96db upstream. Replace the raw atomic_t reference counting of zone write plugs with a refcount_t. No functional changes. Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202411050650.ilIZa8S7-lkp@intel.com/ Signed-off-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20241107065438.236348-1-dlemoal@kernel.org Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af upstream.
blkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To
walk up, it uses blkcg_parent(blkcg) but it was calling that after
blkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the
following UAF:
==================================================================
BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270
Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117
CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022
Workqueue: cgwb_release cgwb_release_workfn
Call Trace:
<TASK>
dump_stack_lvl+0x27/0x80
print_report+0x151/0x710
kasan_report+0xc0/0x100
blkcg_unpin_online+0x15a/0x270
cgwb_release_workfn+0x194/0x480
process_scheduled_works+0x71b/0xe20
worker_thread+0x82a/0xbd0
kthread+0x242/0x2c0
ret_from_fork+0x33/0x70
ret_from_fork_asm+0x1a/0x30
</TASK>
...
Freed by task 1944:
kasan_save_track+0x2b/0x70
kasan_save_free_info+0x3c/0x50
__kasan_slab_free+0x33/0x50
kfree+0x10c/0x330
css_free_rwork_fn+0xe6/0xb30
process_scheduled_works+0x71b/0xe20
worker_thread+0x82a/0xbd0
kthread+0x242/0x2c0
ret_from_fork+0x33/0x70
ret_from_fork_asm+0x1a/0x30
Note that the UAF is not easy to trigger as the free path is indirected
behind a couple RCU grace periods and a work item execution. I could only
trigger it with artifical msleep() injected in blkcg_unpin_online().
Fix it by reading the parent pointer before destroying the blkcg's blkg's.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Abagail ren <renzezhongucas@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Fixes: 4308a434e5e0 ("blkcg: don't offline parent blkcg first")
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>