Setting IORING_SETUP_SINGLE_ISSUER when creating an io_uring doesn't
actually enable any additional optimizations (aside from being a
requirement for IORING_SETUP_DEFER_TASKRUN). This series leverages
IORING_SETUP_SINGLE_ISSUER's guarantee that only one task submits SQEs
to skip taking the uring_lock mutex for the issue and task work paths.

First, we need to disable this optimization for IORING_SETUP_SQPOLL by
clearing the IORING_SETUP_SINGLE_ISSUER flag. For IORING_SETUP_SQPOLL,
the SQ thread is the one taking the uring_lock mutex in the issue path.
Since concurrent io_uring_register() syscalls are allowed on the thread
that created/enabled the io_uring, some additional synchronization
method would be required to synchronize the two threads. This is
possible in principle by having io_uring_register() schedule a task work
item to suspend the SQ thread, but seems complex for a niche use case.

Then we factor out helpers for interacting with uring_lock to centralize
the logic.

Finally, we implement the optimization for IORING_SETUP_SINGLE_ISSUER.
If the io_ring_ctx is setup with IORING_SETUP_SINGLE_ISSUER, skip the
uring_lock mutex_lock() and mutex_unlock() on the submitter_task. On
other tasks acquiring the ctx uring lock, use a task work item to
suspend the submitter_task for the critical section.
If the io_ring_ctx is IORING_SETUP_R_DISABLED (possible during
io_uring_setup(), io_uring_register(), or io_uring exit), submitter_task
may be set concurrently, so acquire the uring_lock before checking it.
If submitter_task isn't set yet, the uring_lock suffices to provide
mutual exclusion. If task work can't be queued because submitter_task
has exited, also use the uring_lock for mutual exclusion.

v6:
- Release submitter_task reference last in io_ring_ctx_free() (syzbot)
- Use the uring_lock to provide mutual exclusion if task_work_add()
  fails because submitter_task has exited
- Add Reviewed-by tag

v5:
- Ensure submitter_task is initialized in io_uring_create() before
  calling io_ring_ctx_wait_and_kill() (kernel test robot)
- Correct Fixes tag (Joanne)
- Add Reviewed-by tag

v4:
- Handle IORING_SETUP_SINGLE_ISSUER and IORING_SETUP_R_DISABLED
  correctly (syzbot)
- Remove separate set of helpers for io_uring_register()
- Add preliminary fix to prevent races between accessing ctx->flags and
  submitter_task

v3:
- Ensure mutual exclusion on threads other than submitter_task via a
  task work item to suspend submitter_task
- Drop patches already merged

v2:
- Don't enable these optimizations for IORING_SETUP_SQPOLL, as we still
  need to synchronize SQ thread submission with io_uring_register()

Caleb Sander Mateos (6):
  io_uring: use release-acquire ordering for IORING_SETUP_R_DISABLED
  io_uring: clear IORING_SETUP_SINGLE_ISSUER for IORING_SETUP_SQPOLL
  io_uring: ensure submitter_task is valid for io_ring_ctx's lifetime
  io_uring: use io_ring_submit_lock() in io_iopoll_req_issued()
  io_uring: factor out uring_lock helpers
  io_uring: avoid uring_lock for IORING_SETUP_SINGLE_ISSUER

 include/linux/io_uring_types.h |  12 +-
 io_uring/cancel.c              |  40 +++---
 io_uring/cancel.h              |   5 +-
 io_uring/eventfd.c             |   5 +-
 io_uring/fdinfo.c              |   8 +-
 io_uring/filetable.c           |   8 +-
 io_uring/futex.c               |  14 +-
 io_uring/io_uring.c            | 232 ++++++++++++++++++++-------------
 io_uring/io_uring.h            | 187 +++++++++++++++++++++++---
 io_uring/kbuf.c                |  32 +++--
 io_uring/memmap.h              |   2 +-
 io_uring/msg_ring.c            |  33 +++--
 io_uring/notif.c               |   5 +-
 io_uring/notif.h               |   3 +-
 io_uring/openclose.c           |  14 +-
 io_uring/poll.c                |  21 +--
 io_uring/register.c            |  81 ++++++------
 io_uring/rsrc.c                |  51 +++++---
 io_uring/rsrc.h                |   6 +-
 io_uring/rw.c                  |   2 +-
 io_uring/splice.c              |   5 +-
 io_uring/sqpoll.c              |   5 +-
 io_uring/tctx.c                |  27 ++--
 io_uring/tctx.h                |   5 +-
 io_uring/uring_cmd.c           |  13 +-
 io_uring/waitid.c              |  13 +-
 io_uring/zcrx.c                |   2 +-
 27 files changed, 555 insertions(+), 276 deletions(-)

-- 
2.45.2

syzbot ci has tested the following series

[v6] io_uring: avoid uring_lock for IORING_SETUP_SINGLE_ISSUER
https://lore.kernel.org/all/20251218024459.1083572-1-csander@purestorage.com
* [PATCH v6 1/6] io_uring: use release-acquire ordering for IORING_SETUP_R_DISABLED
* [PATCH v6 2/6] io_uring: clear IORING_SETUP_SINGLE_ISSUER for IORING_SETUP_SQPOLL
* [PATCH v6 3/6] io_uring: ensure submitter_task is valid for io_ring_ctx's lifetime
* [PATCH v6 4/6] io_uring: use io_ring_submit_lock() in io_iopoll_req_issued()
* [PATCH v6 5/6] io_uring: factor out uring_lock helpers
* [PATCH v6 6/6] io_uring: avoid uring_lock for IORING_SETUP_SINGLE_ISSUER

and found the following issue:
INFO: task hung in io_wq_put_and_exit

Full report is available here:
https://ci.syzbot.org/series/21eac721-670b-4f34-9696-66f9b28233ac

***

INFO: task hung in io_wq_put_and_exit

tree:      torvalds
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base:      d358e5254674b70f34c847715ca509e46eb81e6f
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/1710cffe-7d78-4489-9aa1-823b8c2532ed/config
syz repro: https://ci.syzbot.org/findings/74ae8703-9484-4d82-aa78-84cc37dcb1ef/syz_repro

INFO: task syz.1.18:6046 blocked for more than 143 seconds.
      Not tainted syzkaller #0
      Blocked by coredump.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.18        state:D stack:25672 pid:6046  tgid:6045  ppid:5971   task_flags:0x400548 flags:0x00080004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_wq_exit_workers io_uring/io-wq.c:1328 [inline]
 io_wq_put_and_exit+0x316/0x650 io_uring/io-wq.c:1356
 io_uring_clean_tctx+0x11f/0x1a0 io_uring/tctx.c:207
 io_uring_cancel_generic+0x6ca/0x7d0 io_uring/cancel.c:652
 io_uring_files_cancel include/linux/io_uring.h:19 [inline]
 do_exit+0x345/0x2310 kernel/exit.c:911
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 get_signal+0x1285/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x87/0x4f0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2e3/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6a8b58f7c9
RSP: 002b:00007f6a8c4a00e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007f6a8b7e5fa8 RCX: 00007f6a8b58f7c9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f6a8b7e5fac
RBP: 00007f6a8b7e5fa0 R08: 3fffffffffffffff R09: 0000000000000000
R10: 0000000000000800 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6a8b7e6038 R14: 00007ffcac96d220 R15: 00007ffcac96d308
 </TASK>
INFO: task iou-wrk-6046:6047 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:iou-wrk-6046    state:D stack:27760 pid:6047  tgid:6045  ppid:5971   task_flags:0x404050 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_ring_ctx_lock_nested+0x2b3/0x380 io_uring/io_uring.h:283
 io_ring_ctx_lock io_uring/io_uring.h:290 [inline]
 io_ring_submit_lock io_uring/io_uring.h:554 [inline]
 io_files_update+0x677/0x7f0 io_uring/rsrc.c:504
 __io_issue_sqe+0x181/0x4b0 io_uring/io_uring.c:1818
 io_issue_sqe+0x1de/0x1190 io_uring/io_uring.c:1841
 io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1953
 io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:650
 io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:704
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
INFO: task syz.0.17:6049 blocked for more than 143 seconds.
      Not tainted syzkaller #0
      Blocked by coredump.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17        state:D stack:25592 pid:6049  tgid:6048  ppid:5967   task_flags:0x400548 flags:0x00080004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_wq_exit_workers io_uring/io-wq.c:1328 [inline]
 io_wq_put_and_exit+0x316/0x650 io_uring/io-wq.c:1356
 io_uring_clean_tctx+0x11f/0x1a0 io_uring/tctx.c:207
 io_uring_cancel_generic+0x6ca/0x7d0 io_uring/cancel.c:652
 io_uring_files_cancel include/linux/io_uring.h:19 [inline]
 do_exit+0x345/0x2310 kernel/exit.c:911
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 get_signal+0x1285/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x87/0x4f0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2e3/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa96a98f7c9
RSP: 002b:00007fa96b7430e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007fa96abe5fa8 RCX: 00007fa96a98f7c9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fa96abe5fac
RBP: 00007fa96abe5fa0 R08: 3fffffffffffffff R09: 0000000000000000
R10: 0000000000000800 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa96abe6038 R14: 00007ffd9fcc00d0 R15: 00007ffd9fcc01b8
 </TASK>
INFO: task iou-wrk-6049:6050 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:iou-wrk-6049    state:D stack:27760 pid:6050  tgid:6048  ppid:5967   task_flags:0x404050 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_ring_ctx_lock_nested+0x2b3/0x380 io_uring/io_uring.h:283
 io_ring_ctx_lock io_uring/io_uring.h:290 [inline]
 io_ring_submit_lock io_uring/io_uring.h:554 [inline]
 io_files_update+0x677/0x7f0 io_uring/rsrc.c:504
 __io_issue_sqe+0x181/0x4b0 io_uring/io_uring.c:1818
 io_issue_sqe+0x1de/0x1190 io_uring/io_uring.c:1841
 io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1953
 io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:650
 io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:704
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
INFO: task syz.2.19:6052 blocked for more than 144 seconds.
      Not tainted syzkaller #0
      Blocked by coredump.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.19        state:D stack:26208 pid:6052  tgid:6051  ppid:5972   task_flags:0x400548 flags:0x00080004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_wq_exit_workers io_uring/io-wq.c:1328 [inline]
 io_wq_put_and_exit+0x316/0x650 io_uring/io-wq.c:1356
 io_uring_clean_tctx+0x11f/0x1a0 io_uring/tctx.c:207
 io_uring_cancel_generic+0x6ca/0x7d0 io_uring/cancel.c:652
 io_uring_files_cancel include/linux/io_uring.h:19 [inline]
 do_exit+0x345/0x2310 kernel/exit.c:911
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 get_signal+0x1285/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x87/0x4f0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2e3/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4b5cb8f7c9
RSP: 002b:00007f4b5d9a80e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007f4b5cde5fa8 RCX: 00007f4b5cb8f7c9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f4b5cde5fac
RBP: 00007f4b5cde5fa0 R08: 3fffffffffffffff R09: 0000000000000000
R10: 0000000000000800 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4b5cde6038 R14: 00007ffcdd64aed0 R15: 00007ffcdd64afb8
 </TASK>
INFO: task iou-wrk-6052:6053 blocked for more than 144 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:iou-wrk-6052    state:D stack:27760 pid:6053  tgid:6051  ppid:5972   task_flags:0x404050 flags:0x00080006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
 io_ring_ctx_lock_nested+0x2b3/0x380 io_uring/io_uring.h:283
 io_ring_ctx_lock io_uring/io_uring.h:290 [inline]
 io_ring_submit_lock io_uring/io_uring.h:554 [inline]
 io_files_update+0x677/0x7f0 io_uring/rsrc.c:504
 __io_issue_sqe+0x181/0x4b0 io_uring/io_uring.c:1818
 io_issue_sqe+0x1de/0x1190 io_uring/io_uring.c:1841
 io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1953
 io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:650
 io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:704
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/35:
 #0: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
5 locks held by kworker/u10:8/1120:
 #0: ffff88823c63a918 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:639
 #1: ffff88823c624588 (psi_seq){-.-.}-{0:0}, at: psi_task_switch+0x53/0x880 kernel/sched/psi.c:933
 #2: ffff88810ac50788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: class_wiphy_constructor include/net/cfg80211.h:6363 [inline]
 #2: ffff88810ac50788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: cfg80211_wiphy_work+0xb4/0x450 net/wireless/core.c:424
 #3: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #3: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #3: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: ieee80211_sta_active_ibss+0xc3/0x330 net/mac80211/ibss.c:635
 #4: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #4: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #4: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
 #4: ffffffff8df419e0 (rcu_read_lock){....}-{1:3}, at: unwind_next_frame+0xa5/0x2390 arch/x86/kernel/unwind_orc.c:479
2 locks held by getty/5656:
 #0: ffff8881133040a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc900035732f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x449/0x1460 drivers/tty/n_tty.c:2211
3 locks held by kworker/0:9/6480:
 #0: ffff888100075948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline]
 #0: ffff888100075948 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340
 #1: ffffc9000546fb80 (deferred_process_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline]
 #1: ffffc9000546fb80 (deferred_process_work){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340
 #2: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: switchdev_deferred_process_work+0xe/0x20 net/switchdev/switchdev.c:104
1 lock held by syz-executor/6649:
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x8ec/0x1c90 net/core/rtnetlink.c:4071
2 locks held by syz-executor/6651:
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #0: ffffffff8f30ffc8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x8ec/0x1c90 net/core/rtnetlink.c:4071
 #1: ffff88823c63a918 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:639
4 locks held by syz-executor/6653:

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 35 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xf95/0xfe0 kernel/hung_task.c:515
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 6653 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:io_serial_out+0x7c/0xc0 drivers/tty/serial/8250/8250_port.c:407
Code: 3f a6 fc 44 89 f9 d3 e5 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 ec 91 0c fd 41 03 2e 89 d8 89 ea ee <5b> 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc 44 89 f9 80 e1 07 38 c1
RSP: 0018:ffffc90008156590 EFLAGS: 00000002
RAX: 000000000000005b RBX: 000000000000005b RCX: 0000000000000000
RDX: 00000000000003f8 RSI: 0000000000000000 RDI: 0000000000000020
RBP: 00000000000003f8 R08: ffff888102f08237 R09: 1ffff110205e1046
R10: dffffc0000000000 R11: ffffffff851b9060 R12: dffffc0000000000
R13: ffffffff998dd9e1 R14: ffffffff99bf2420 R15: 0000000000000000
FS:  0000555595186500(0000) GS:ffff8882a9e37000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055599f9c9018 CR3: 0000000112ed8000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 serial_port_out include/linux/serial_core.h:811 [inline]
 serial8250_console_putchar drivers/tty/serial/8250/8250_port.c:3192 [inline]
 serial8250_console_fifo_write drivers/tty/serial/8250/8250_port.c:-1 [inline]
 serial8250_console_write+0x1410/0x1ba0 drivers/tty/serial/8250/8250_port.c:3342
 console_emit_next_record kernel/printk/printk.c:3129 [inline]
 console_flush_one_record kernel/printk/printk.c:3215 [inline]
 console_flush_all+0x745/0xb60 kernel/printk/printk.c:3289
 __console_flush_and_unlock kernel/printk/printk.c:3319 [inline]
 console_unlock+0xbb/0x190 kernel/printk/printk.c:3359
 vprintk_emit+0x4f8/0x5f0 kernel/printk/printk.c:2426
 _printk+0xcf/0x120 kernel/printk/printk.c:2451
 br_set_state+0x475/0x710 net/bridge/br_stp.c:57
 br_init_port+0x99/0x200 net/bridge/br_stp_if.c:39
 new_nbp+0x2f9/0x440 net/bridge/br_if.c:443
 br_add_if+0x283/0xeb0 net/bridge/br_if.c:586
 do_set_master+0x533/0x6d0 net/core/rtnetlink.c:2963
 do_setlink+0xcf0/0x41c0 net/core/rtnetlink.c:3165
 rtnl_changelink net/core/rtnetlink.c:3776 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3935 [inline]
 rtnl_newlink+0x161c/0x1c90 net/core/rtnetlink.c:4072
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 __sys_sendto+0x3bd/0x520 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2209
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f780c39165c
Code: 2a 5f 02 00 44 8b 4c 24 2c 4c 8b 44 24 20 89 c5 44 8b 54 24 28 48 8b 54 24 18 b8 2c 00 00 00 48 8b 74 24 10 8b 7c 24 08 0f 05 <48> 3d 00 f0 ff ff 77 34 89 ef 48 89 44 24 08 e8 70 5f 02 00 48 8b
RSP: 002b:00007ffcecb618b0 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f780d114620 RCX: 00007f780c39165c
RDX: 0000000000000028 RSI: 00007f780d114670 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007ffcecb61904 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000003
R13: 0000000000000000 R14: 00007f780d114670 R15: 0000000000000000
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
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