nvme-tcp: teardown circular locking fixes

When a controller reset is triggered via sysfs (by writing to
/sys/class/nvme/<nvmedev>/reset_controller), the reset work tears down
and re-establishes all queues. The socket release using fput() defers
the actual cleanup to task_work delayed_fput workqueue. This deferred
cleanup can race with the subsequent queue re-allocation during reset,
potentially leading to use-after-free or resource conflicts.

Replace fput() with __fput_sync() to ensure synchronous socket release,
guaranteeing that all socket resources are fully cleaned up before the
function returns. This prevents races during controller reset where
new queue setup may begin before the old socket is fully released.

* Call chain during reset:
nvme_reset_ctrl_work()
-> nvme_tcp_teardown_ctrl()
-> nvme_tcp_teardown_io_queues()
-> nvme_tcp_free_io_queues()
-> nvme_tcp_free_queue() <-- fput() -> __fput_sync()
-> nvme_tcp_teardown_admin_queue()
-> nvme_tcp_free_admin_queue()
-> nvme_tcp_free_queue() <-- fput() -> __fput_sync()
-> nvme_tcp_setup_ctrl() <-- race with deferred fput

memalloc_noreclaim_save() sets PF_MEMALLOC which is intended for tasks
performing memory reclaim work that need reserve access. While PF_MEMALLOC
prevents the task from entering direct reclaim (causing __need_reclaim() to
return false), it does not strip __GFP_IO from gfp flags. The allocator can
therefore still trigger writeback I/O when __GFP_IO remains set, which is
unsafe when the caller holds block layer locks.

Switch to memalloc_noio_save() which sets PF_MEMALLOC_NOIO. This causes
current_gfp_context() to strip __GFP_IO|__GFP_FS from every allocation in
the scope, making it safe to allocate memory while holding elevator_lock and
set->srcu.

* The issue can be reproduced using blktests:

nvme_trtype=tcp ./check nvme/005
blktests (master) # nvme_trtype=tcp ./check nvme/005
nvme/005 (tr=tcp) (reset local loopback target) [failed]
runtime 0.725s ... 0.798s
something found in dmesg:
[ 108.473940] run blktests nvme/005 at 2025-11-22 16:12:20

[...]
...
(See '/root/blktests/results/nodev_tr_tcp/nvme/005.dmesg' for the entire message)
blktests (master) # cat /root/blktests/results/nodev_tr_tcp/nvme/005.dmesg
[ 108.473940] run blktests nvme/005 at 2025-11-22 16:12:20
[ 108.526983] loop0: detected capacity change from 0 to 2097152
[ 108.555606] nvmet: adding nsid 1 to subsystem blktests-subsystem-1
[ 108.572531] nvmet_tcp: enabling port 0 (127.0.0.1:4420)
[ 108.613061] nvmet: Created nvm controller 1 for subsystem blktests-subsystem-1 for NQN nqn.2014-08.org.nvmexpress:uuid:0f01fb42-9f7f-4856-b0b3-51e60b8de349.
[ 108.616832] nvme nvme0: creating 48 I/O queues.
[ 108.630791] nvme nvme0: mapped 48/0/0 default/read/poll queues.
[ 108.661892] nvme nvme0: new ctrl: NQN "blktests-subsystem-1", addr 127.0.0.1:4420, hostnqn: nqn.2014-08.org.nvmexpress:uuid:0f01fb42-9f7f-4856-b0b3-51e60b8de349
[ 108.746639] nvmet: Created nvm controller 2 for subsystem blktests-subsystem-1 for NQN nqn.2014-08.org.nvmexpress:uuid:0f01fb42-9f7f-4856-b0b3-51e60b8de349.
[ 108.748466] nvme nvme0: creating 48 I/O queues.
[ 108.802984] nvme nvme0: mapped 48/0/0 default/read/poll queues.
[ 108.829983] nvme nvme0: Removing ctrl: NQN "blktests-subsystem-1"
[ 108.854288] block nvme0n1: no available path - failing I/O
[ 108.854344] block nvme0n1: no available path - failing I/O
[ 108.854373] Buffer I/O error on dev nvme0n1, logical block 1, async page read

[ 108.891693] ======================================================
[ 108.895912] WARNING: possible circular locking dependency detected
[ 108.900184] 6.17.0nvme+ #3 Tainted: G N
[ 108.903913] ------------------------------------------------------
[ 108.908171] nvme/2734 is trying to acquire lock:
[ 108.911957] ffff88810210e610 (set->srcu){.+.+}-{0:0}, at: __synchronize_srcu+0x17/0x170
[ 108.917587]
but task is already holding lock:
[ 108.921570] ffff88813abea198 (&q->elevator_lock){+.+.}-{4:4}, at: elevator_change+0xa8/0x1c0
[ 108.927361]
which lock already depends on the new lock.

[ 108.933018]
the existing dependency chain (in reverse order) is:
[ 108.938223]
-> #4 (&q->elevator_lock){+.+.}-{4:4}:
[ 108.942988] __mutex_lock+0xa2/0x1150
[ 108.945873] elevator_change+0xa8/0x1c0
[ 108.948925] elv_iosched_store+0xdf/0x140
[ 108.952043] kernfs_fop_write_iter+0x16a/0x220
[ 108.955367] vfs_write+0x378/0x520
[ 108.957598] ksys_write+0x67/0xe0
[ 108.959721] do_syscall_64+0x76/0xbb0
[ 108.962052] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 108.965145]
-> #3 (&q->q_usage_counter(io)){++++}-{0:0}:
[ 108.968923] blk_alloc_queue+0x30e/0x350
[ 108.972117] blk_mq_alloc_queue+0x61/0xd0
[ 108.974677] scsi_alloc_sdev+0x2a0/0x3e0
[ 108.977092] scsi_probe_and_add_lun+0x1bd/0x430
[ 108.979921] __scsi_add_device+0x109/0x120
[ 108.982504] ata_scsi_scan_host+0x97/0x1c0
[ 108.984365] async_run_entry_fn+0x2d/0x130
[ 108.986109] process_one_work+0x20e/0x630
[ 108.987830] worker_thread+0x184/0x330
[ 108.989473] kthread+0x10a/0x250
[ 108.990852] ret_from_fork+0x297/0x300
[ 108.992491] ret_from_fork_asm+0x1a/0x30
[ 108.994159]
-> #2 (fs_reclaim){+.+.}-{0:0}:
[ 108.996320] fs_reclaim_acquire+0x99/0xd0
[ 108.998058] kmem_cache_alloc_node_noprof+0x4e/0x3c0
[ 109.000123] __alloc_skb+0x15f/0x190
[ 109.002195] tcp_send_active_reset+0x3f/0x1e0
[ 109.004038] tcp_disconnect+0x50b/0x720
[ 109.005695] __tcp_close+0x2b8/0x4b0
[ 109.007227] tcp_close+0x20/0x80
[ 109.008663] inet_release+0x31/0x60
[ 109.010175] __sock_release+0x3a/0xc0
[ 109.011778] sock_close+0x14/0x20
[ 109.013263] __fput+0xee/0x2c0
[ 109.014673] delayed_fput+0x31/0x50
[ 109.016183] process_one_work+0x20e/0x630
[ 109.017897] worker_thread+0x184/0x330
[ 109.019543] kthread+0x10a/0x250
[ 109.020929] ret_from_fork+0x297/0x300
[ 109.022565] ret_from_fork_asm+0x1a/0x30
[ 109.024194]
-> #1 (sk_lock-AF_INET-NVME){+.+.}-{0:0}:
[ 109.026634] lock_sock_nested+0x2e/0x70
[ 109.028251] tcp_sendmsg+0x1a/0x40
[ 109.029783] sock_sendmsg+0xed/0x110
[ 109.031321] nvme_tcp_try_send_cmd_pdu+0x13e/0x260 [nvme_tcp]
[ 109.034263] nvme_tcp_try_send+0xb3/0x330 [nvme_tcp]
[ 109.036375] nvme_tcp_queue_rq+0x342/0x3d0 [nvme_tcp]
[ 109.038528] blk_mq_dispatch_rq_list+0x297/0x800
[ 109.040448] __blk_mq_sched_dispatch_requests+0x3db/0x5f0
[ 109.042677] blk_mq_sched_dispatch_requests+0x29/0x70
[ 109.044787] blk_mq_run_work_fn+0x76/0x1b0
[ 109.046535] process_one_work+0x20e/0x630
[ 109.048245] worker_thread+0x184/0x330
[ 109.049890] kthread+0x10a/0x250
[ 109.051331] ret_from_fork+0x297/0x300
[ 109.053024] ret_from_fork_asm+0x1a/0x30
[ 109.054740]
-> #0 (set->srcu){.+.+}-{0:0}:
[ 109.056850] __lock_acquire+0x1468/0x2210
[ 109.058614] lock_sync+0xa5/0x110
[ 109.060048] __synchronize_srcu+0x49/0x170
[ 109.061802] elevator_switch+0xc9/0x330
[ 109.063950] elevator_change+0x128/0x1c0
[ 109.065675] elevator_set_none+0x4c/0x90
[ 109.067316] blk_unregister_queue+0xa8/0x110
[ 109.069165] __del_gendisk+0x14e/0x3c0
[ 109.070824] del_gendisk+0x75/0xa0
[ 109.072328] nvme_ns_remove+0xf2/0x230 [nvme_core]
[ 109.074365] nvme_remove_namespaces+0xf2/0x150 [nvme_core]
[ 109.076652] nvme_do_delete_ctrl+0x71/0x90 [nvme_core]
[ 109.078775] nvme_delete_ctrl_sync+0x3b/0x50 [nvme_core]
[ 109.081009] nvme_sysfs_delete+0x34/0x40 [nvme_core]
[ 109.083082] kernfs_fop_write_iter+0x16a/0x220
[ 109.085009] vfs_write+0x378/0x520
[ 109.086539] ksys_write+0x67/0xe0
[ 109.087982] do_syscall_64+0x76/0xbb0
[ 109.089577] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 109.091665]
other info that might help us debug this:

[ 109.095478] Chain exists of:
set->srcu --> &q->q_usage_counter(io) --> &q->elevator_lock

[ 109.099544] Possible unsafe locking scenario:

[ 109.101708] CPU0 CPU1
[ 109.103402] ---- ----
[ 109.105103] lock(&q->elevator_lock);
[ 109.106530] lock(&q->q_usage_counter(io));
[ 109.109022] lock(&q->elevator_lock);
[ 109.111391] sync(set->srcu);
[ 109.112586]
*** DEADLOCK ***

[ 109.114772] 5 locks held by nvme/2734:
[ 109.116189] #0: ffff888101925410 (sb_writers#4){.+.+}-{0:0}, at: ksys_write+0x67/0xe0
[ 109.119143] #1: ffff88817a914e88 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x10f/0x220
[ 109.123141] #2: ffff8881046313f8 (kn->active#185){++++}-{0:0}, at: sysfs_remove_file_self+0x26/0x50
[ 109.126543] #3: ffff88810470e1d0 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x6d/0xa0
[ 109.129891] #4: ffff88813abea198 (&q->elevator_lock){+.+.}-{4:4}, at: elevator_change+0xa8/0x1c0
[ 109.133149]
stack backtrace:
[ 109.134817] CPU: 6 UID: 0 PID: 2734 Comm: nvme Tainted: G N 6.17.0nvme+ #3 PREEMPT(voluntary)
[ 109.134819] Tainted: [N]=TEST
[ 109.134820] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 109.134821] Call Trace:
[ 109.134823] <TASK>
[ 109.134824] dump_stack_lvl+0x75/0xb0
[ 109.134828] print_circular_bug+0x26a/0x330
[ 109.134831] check_noncircular+0x12f/0x150
[ 109.134834] __lock_acquire+0x1468/0x2210
[ 109.134837] ? __synchronize_srcu+0x17/0x170
[ 109.134838] lock_sync+0xa5/0x110
[ 109.134840] ? __synchronize_srcu+0x17/0x170
[ 109.134842] __synchronize_srcu+0x49/0x170
[ 109.134843] ? mark_held_locks+0x49/0x80
[ 109.134845] ? _raw_spin_unlock_irqrestore+0x2d/0x60
[ 109.134847] ? kvm_clock_get_cycles+0x14/0x30
[ 109.134853] ? ktime_get_mono_fast_ns+0x36/0xb0
[ 109.134858] elevator_switch+0xc9/0x330
[ 109.134860] elevator_change+0x128/0x1c0
[ 109.134862] ? kernfs_put.part.0+0x86/0x290
[ 109.134864] elevator_set_none+0x4c/0x90
[ 109.134866] blk_unregister_queue+0xa8/0x110
[ 109.134868] __del_gendisk+0x14e/0x3c0
[ 109.134870] del_gendisk+0x75/0xa0
[ 109.134872] nvme_ns_remove+0xf2/0x230 [nvme_core]
[ 109.134879] nvme_remove_namespaces+0xf2/0x150 [nvme_core]
[ 109.134887] nvme_do_delete_ctrl+0x71/0x90 [nvme_core]
[ 109.134893] nvme_delete_ctrl_sync+0x3b/0x50 [nvme_core]
[ 109.134899] nvme_sysfs_delete+0x34/0x40 [nvme_core]
[ 109.134905] kernfs_fop_write_iter+0x16a/0x220
[ 109.134908] vfs_write+0x378/0x520
[ 109.134911] ksys_write+0x67/0xe0
[ 109.134913] do_syscall_64+0x76/0xbb0
[ 109.134915] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 109.134916] RIP: 0033:0x7fd68a737317
[ 109.134917] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
[ 109.134919] RSP: 002b:00007ffded1546d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 109.134920] RAX: ffffffffffffffda RBX: 000000000054f7e0 RCX: 00007fd68a737317
[ 109.134921] RDX: 0000000000000001 RSI: 00007fd68a855719 RDI: 0000000000000003
[ 109.134921] RBP: 0000000000000003 R08: 0000000030407850 R09: 00007fd68a7cd4e0
[ 109.134922] R10: 00007fd68a65b130 R11: 0000000000000246 R12: 00007fd68a855719
[ 109.134923] R13: 00000000304074c0 R14: 00000000304074c0 R15: 0000000030408660
[ 109.134926] </TASK>
[ 109.962756] Key type psk unregistered

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>