Nilay Shroff 370ac285f2 block: avoid cpu_hotplug_lock depedency on freeze_lock ... A recent lockdep[1] splat observed while running blktest block/005 reveals a potential deadlock caused by the cpu_hotplug_lock dependency on ->freeze_lock. This dependency was introduced by commit 033b667a82 ("block: blk-rq-qos: guard rq-qos helpers by static key"). That change added a static key to avoid fetching q->rq_qos when neither blk-wbt nor blk-iolatency is configured. The static key dynamically patches kernel text to a NOP when disabled, eliminating overhead of fetching q->rq_qos in the I/O hot path. However, enabling a static key at runtime requires acquiring both cpu_hotplug_lock and jump_label_mutex. When this happens after the queue has already been frozen (i.e., while holding ->freeze_lock), it creates a locking dependency from cpu_hotplug_lock to ->freeze_lock, which leads to a potential deadlock reported by lockdep [1]. To resolve this, replace the static key mechanism with q->queue_flags: QUEUE_FLAG_QOS_ENABLED. This flag is evaluated in the fast path before accessing q->rq_qos. If the flag is set, we proceed to fetch q->rq_qos; otherwise, the access is skipped. Since q->queue_flags is commonly accessed in IO hotpath and resides in the first cacheline of struct request_queue, checking it imposes minimal overhead while eliminating the deadlock risk. This change avoids the lockdep splat without introducing performance regressions. [1] https://lore.kernel.org/linux-block/4fdm37so3o4xricdgfosgmohn63aa7wj3ua4e5vpihoamwg3ui@fq42f5q5t5ic/ Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com> Closes: https://lore.kernel.org/linux-block/4fdm37so3o4xricdgfosgmohn63aa7wj3ua4e5vpihoamwg3ui@fq42f5q5t5ic/ Fixes: 033b667a82 ("block: blk-rq-qos: guard rq-qos helpers by static key") Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Yu Kuai <yukuai3@huawei.com> Link: https://lore.kernel.org/r/20250814082612.500845-4-nilay@linux.ibm.com Signed-off-by: Jens Axboe <axboe@kernel.dk>		2025-08-21 07:11:11 -06:00
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acpi	mailbox/pcc: support mailbox management of the shared buffer	2025-08-07 23:49:56 -05:00
asm-generic	…
clocksource	…
crypto	This push fixes a regression that breaks hmac(sha3-224-s390).	2025-08-09 07:26:19 +03:00
cxl	…
drm	…
dt-bindings	Pin control changes for v6.17	2025-08-02 12:07:09 -07:00
hyperv	…
keys	…
kunit	…
kvm	…
linux	block: avoid cpu_hotplug_lock depedency on freeze_lock	2025-08-21 07:11:11 -06:00
math-emu	…
media	…
memory	…
misc	…
net	Previous releases - regressions:	2025-08-08 07:03:25 +03:00
pcmcia	…
ras	…
rdma	…
rv	…
scsi	…
soc	…
sound	ASoC: Fixes for v6.17	2025-08-06 20:20:25 +02:00
target	…
trace	…
uapi	md: keep recovery_cp in mdp_superblock_s	2025-08-16 08:47:38 +08:00
ufs	…
vdso	…
video	…
xen	Significant patch series in this pull request:	2025-08-03 16:23:09 -07:00
Kbuild	…