[PATCH] nvmet: avoid recursive nvmet-wq flush in nvmet_ctrl_free

[PATCH] nvmet: avoid recursive nvmet-wq flush in nvmet_ctrl_free

[Chaitanya Kulkarni]

nvmet_tcp_release_queue_work() runs on nvmet-wq and can drop the
final controller reference through nvmet_cq_put(). If that triggers
nvmet_ctrl_free(), the teardown path flushes ctrl->async_event_work on
the same nvmet-wq.

Call chain:

 nvmet_tcp_schedule_release_queue()
   kref_put(&queue->kref, nvmet_tcp_release_queue)
     nvmet_tcp_release_queue()
       queue_work(nvmet_wq, &queue->release_work) <--- nvmet_wq
         process_one_work()
           nvmet_tcp_release_queue_work()
             nvmet_cq_put(&queue->nvme_cq)
               nvmet_cq_destroy()
                 nvmet_ctrl_put(cq->ctrl)
                   nvmet_ctrl_free()
                     flush_work(&ctrl->async_event_work) <--- nvmet_wq

                      Previously Scheduled by :-
		        nvmet_add_async_event
		          queue_work(nvmet_wq, &ctrl->async_event_work);

This trips lockdep with a possible recursive locking warning.

[ 5223.015876] run blktests nvme/003 at 2026-04-07 20:53:55
[ 5223.061801] loop0: detected capacity change from 0 to 2097152
[ 5223.072206] nvmet: adding nsid 1 to subsystem blktests-subsystem-1
[ 5223.088368] nvmet_tcp: enabling port 0 (127.0.0.1:4420)
[ 5223.126086] nvmet: Created discovery controller 1 for subsystem nqn.2014-08.org.nvmexpress.discovery for NQN nqn.2014-08.org.nvmexpress:uuid:0f01fb42-9f7f-4856-b0b3-51e60b8de349.
[ 5223.128453] nvme nvme1: new ctrl: NQN "nqn.2014-08.org.nvmexpress.discovery", addr 127.0.0.1:4420, hostnqn: nqn.2014-08.org.nvmexpress:uuid:0f01fb42-9f7f-4856-b0b3-51e60b8de349
[ 5233.199447] nvme nvme1: Removing ctrl: NQN "nqn.2014-08.org.nvmexpress.discovery"

[ 5233.227718] ============================================
[ 5233.231283] WARNING: possible recursive locking detected
[ 5233.234696] 7.0.0-rc3nvme+ #20 Tainted: G           O     N
[ 5233.238434] --------------------------------------------
[ 5233.241852] kworker/u192:6/2413 is trying to acquire lock:
[ 5233.245429] ffff888111632548 ((wq_completion)nvmet-wq){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x26/0x90
[ 5233.251438]
               but task is already holding lock:
[ 5233.255254] ffff888111632548 ((wq_completion)nvmet-wq){+.+.}-{0:0}, at: process_one_work+0x5cc/0x6e0
[ 5233.261125]
               other info that might help us debug this:
[ 5233.265333]  Possible unsafe locking scenario:

[ 5233.269217]        CPU0
[ 5233.270795]        ----
[ 5233.272436]   lock((wq_completion)nvmet-wq);
[ 5233.275241]   lock((wq_completion)nvmet-wq);
[ 5233.278020]
                *** DEADLOCK ***

[ 5233.281793]  May be due to missing lock nesting notation

[ 5233.286195] 3 locks held by kworker/u192:6/2413:
[ 5233.289192]  #0: ffff888111632548 ((wq_completion)nvmet-wq){+.+.}-{0:0}, at: process_one_work+0x5cc/0x6e0
[ 5233.294569]  #1: ffffc9000e2a7e40 ((work_completion)(&queue->release_work)){+.+.}-{0:0}, at: process_one_work+0x1c5/0x6e0
[ 5233.300128]  #2: ffffffff82d7dc40 (rcu_read_lock){....}-{1:3}, at: __flush_work+0x62/0x530
[ 5233.304290]
               stack backtrace:
[ 5233.306520] CPU: 4 UID: 0 PID: 2413 Comm: kworker/u192:6 Tainted: G           O     N  7.0.0-rc3nvme+ #20 PREEMPT(full)
[ 5233.306524] Tainted: [O]=OOT_MODULE, [N]=TEST
[ 5233.306525] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
[ 5233.306527] Workqueue: nvmet-wq nvmet_tcp_release_queue_work [nvmet_tcp]
[ 5233.306532] Call Trace:
[ 5233.306534]  <TASK>
[ 5233.306536]  dump_stack_lvl+0x73/0xb0
[ 5233.306552]  print_deadlock_bug+0x225/0x2f0
[ 5233.306556]  __lock_acquire+0x13f0/0x2290
[ 5233.306563]  lock_acquire+0xd0/0x300
[ 5233.306565]  ? touch_wq_lockdep_map+0x26/0x90
[ 5233.306571]  ? __flush_work+0x20b/0x530
[ 5233.306573]  ? touch_wq_lockdep_map+0x26/0x90
[ 5233.306577]  touch_wq_lockdep_map+0x3b/0x90
[ 5233.306580]  ? touch_wq_lockdep_map+0x26/0x90
[ 5233.306583]  ? __flush_work+0x20b/0x530
[ 5233.306585]  __flush_work+0x268/0x530
[ 5233.306588]  ? __pfx_wq_barrier_func+0x10/0x10
[ 5233.306594]  ? xen_error_entry+0x30/0x60
[ 5233.306600]  nvmet_ctrl_free+0x140/0x310 [nvmet]
[ 5233.306617]  nvmet_cq_put+0x74/0x90 [nvmet]
[ 5233.306629]  nvmet_tcp_release_queue_work+0x19f/0x360 [nvmet_tcp]
[ 5233.306634]  process_one_work+0x206/0x6e0
[ 5233.306640]  worker_thread+0x184/0x320
[ 5233.306643]  ? __pfx_worker_thread+0x10/0x10
[ 5233.306646]  kthread+0xf1/0x130
[ 5233.306648]  ? __pfx_kthread+0x10/0x10
[ 5233.306651]  ret_from_fork+0x355/0x450
[ 5233.306653]  ? __pfx_kthread+0x10/0x10
[ 5233.306656]  ret_from_fork_asm+0x1a/0x30
[ 5233.306664]  </TASK>

There is also no need to flush async_event_work from controller
teardown. The admin queue teardown already fails outstanding AER
requests before the final controller put :-

 nvmet_sq_destroy(admin sq)
    nvmet_async_events_failall(ctrl)

The controller has already been removed from the subsystem list before
nvmet_ctrl_free() quiesces outstanding work.

Replace flush_work() with cancel_work_sync() so a pending
async_event_work item is canceled and a running instance is waited on
without recursing into the same workqueue.

Fixes: 06406d81a2d7 ("nvmet: cancel fatal error and flush async work before free controller")
Cc: stable@vger.kernel.org
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
---
 drivers/nvme/target/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 33db6c5534e2..a87567f40c91 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -1749,7 +1749,7 @@ static void nvmet_ctrl_free(struct kref *ref)
 
 	nvmet_stop_keep_alive_timer(ctrl);
 
-	flush_work(&ctrl->async_event_work);
+	cancel_work_sync(&ctrl->async_event_work);
 	cancel_work_sync(&ctrl->fatal_err_work);
 
 	nvmet_destroy_auth(ctrl);
-- 
2.39.5

Re: [PATCH] nvmet: avoid recursive nvmet-wq flush in nvmet_ctrl_free

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>