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Mohamed Khalfella 3baeec23a8 block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list_lock 
[ Upstream commit 59e25ef2b4 ]

blk_mq_{add,del}_queue_tag_set() functions add and remove queues from
tagset, the functions make sure that tagset and queues are marked as
shared when two or more queues are attached to the same tagset.
Initially a tagset starts as unshared and when the number of added
queues reaches two, blk_mq_add_queue_tag_set() marks it as shared along
with all the queues attached to it. When the number of attached queues
drops to 1 blk_mq_del_queue_tag_set() need to mark both the tagset and
the remaining queues as unshared.

Both functions need to freeze current queues in tagset before setting on
unsetting BLK_MQ_F_TAG_QUEUE_SHARED flag. While doing so, both functions
hold set->tag_list_lock mutex, which makes sense as we do not want
queues to be added or deleted in the process. This used to work fine
until commit 98d81f0df7 ("nvme: use blk_mq_[un]quiesce_tagset")
made the nvme driver quiesce tagset instead of quiscing individual
queues. blk_mq_quiesce_tagset() does the job and quiesce the queues in
set->tag_list while holding set->tag_list_lock also.

This results in deadlock between two threads with these stacktraces:

  __schedule+0x47c/0xbb0
  ? timerqueue_add+0x66/0xb0
  schedule+0x1c/0xa0
  schedule_preempt_disabled+0xa/0x10
  __mutex_lock.constprop.0+0x271/0x600
  blk_mq_quiesce_tagset+0x25/0xc0
  nvme_dev_disable+0x9c/0x250
  nvme_timeout+0x1fc/0x520
  blk_mq_handle_expired+0x5c/0x90
  bt_iter+0x7e/0x90
  blk_mq_queue_tag_busy_iter+0x27e/0x550
  ? __blk_mq_complete_request_remote+0x10/0x10
  ? __blk_mq_complete_request_remote+0x10/0x10
  ? __call_rcu_common.constprop.0+0x1c0/0x210
  blk_mq_timeout_work+0x12d/0x170
  process_one_work+0x12e/0x2d0
  worker_thread+0x288/0x3a0
  ? rescuer_thread+0x480/0x480
  kthread+0xb8/0xe0
  ? kthread_park+0x80/0x80
  ret_from_fork+0x2d/0x50
  ? kthread_park+0x80/0x80
  ret_from_fork_asm+0x11/0x20

  __schedule+0x47c/0xbb0
  ? xas_find+0x161/0x1a0
  schedule+0x1c/0xa0
  blk_mq_freeze_queue_wait+0x3d/0x70
  ? destroy_sched_domains_rcu+0x30/0x30
  blk_mq_update_tag_set_shared+0x44/0x80
  blk_mq_exit_queue+0x141/0x150
  del_gendisk+0x25a/0x2d0
  nvme_ns_remove+0xc9/0x170
  nvme_remove_namespaces+0xc7/0x100
  nvme_remove+0x62/0x150
  pci_device_remove+0x23/0x60
  device_release_driver_internal+0x159/0x200
  unbind_store+0x99/0xa0
  kernfs_fop_write_iter+0x112/0x1e0
  vfs_write+0x2b1/0x3d0
  ksys_write+0x4e/0xb0
  do_syscall_64+0x5b/0x160
  entry_SYSCALL_64_after_hwframe+0x4b/0x53

The top stacktrace is showing nvme_timeout() called to handle nvme
command timeout. timeout handler is trying to disable the controller and
as a first step, it needs to blk_mq_quiesce_tagset() to tell blk-mq not
to call queue callback handlers. The thread is stuck waiting for
set->tag_list_lock as it tries to walk the queues in set->tag_list.

The lock is held by the second thread in the bottom stack which is
waiting for one of queues to be frozen. The queue usage counter will
drop to zero after nvme_timeout() finishes, and this will not happen
because the thread will wait for this mutex forever.

Given that [un]quiescing queue is an operation that does not need to
sleep, update blk_mq_[un]quiesce_tagset() to use RCU instead of taking
set->tag_list_lock, update blk_mq_{add,del}_queue_tag_set() to use RCU
safe list operations. Also, delete INIT_LIST_HEAD(&q->tag_set_list)
in blk_mq_del_queue_tag_set() because we can not re-initialize it while
the list is being traversed under RCU. The deleted queue will not be
added/deleted to/from a tagset and it will be freed in blk_free_queue()
after the end of RCU grace period.

Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
Fixes: 98d81f0df7 ("nvme: use blk_mq_[un]quiesce_tagset")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-12-18 13:55:21 +01:00
arch ARM: 9464/1: fix input-only operand modification in load_unaligned_zeropad() 2025-12-18 13:55:20 +01:00
block block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list_lock 2025-12-18 13:55:21 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate_id 2025-12-18 13:54:47 +01:00
Documentation docs: hwmon: fix link to g762 devicetree binding 2025-12-18 13:55:20 +01:00
drivers rtc: gamecube: Check the return value of ioremap() 2025-12-18 13:55:20 +01:00
fs cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB2 2025-12-18 13:55:20 +01:00
include ALSA: uapi: Fix typo in asound.h comment 2025-12-18 13:55:20 +01:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/napi: fix io_napi_entry RCU accesses 2025-11-24 10:36:06 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel dma/pool: eliminate alloc_pages warning in atomic_pool_expand 2025-12-18 13:55:20 +01:00
lib lib/vsprintf: Check pointer before dereferencing in time_and_date() 2025-12-18 13:54:57 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/huge_memory: fix NULL pointer deference when splitting folio 2025-12-07 06:25:02 +09:00
net net/sched: sch_cake: Fix incorrect qlen reduction in cake_drop 2025-12-18 13:55:14 +01:00
rust rust: kbuild: workaround rustdoc doctests modifier bug 2025-11-24 10:36:07 +01:00
samples samples: work around glibc redefining some of our defines wrong 2025-12-12 18:37:21 +01:00
scripts kconfig/nconf: Initialize the default locale at startup 2025-12-01 11:43:36 +01:00
security ima: Handle error code returned by ima_filter_rule_match() 2025-12-18 13:55:04 +01:00
sound ALSA: firewire-motu: add bounds check in put_user loop for DSP events 2025-12-18 13:55:20 +01:00
tools perf hist: In init, ensure mem_info is put on error paths 2025-12-18 13:55:14 +01:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying 2025-11-24 10:36:06 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:25:02 +09:00
Makefile Linux 6.12.62 2025-12-12 18:37:22 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.