• Sagi Grimberg's avatar
    nvmet-rdma: use a private workqueue for delete · 2acf70ad
    Sagi Grimberg authored
    Queue deletion is done asynchronous when the last reference on the queue
    is dropped.  Thus, in order to make sure we don't over allocate under a
    connect/disconnect storm, we let queue deletion complete before making
    forward progress.
    
    However, given that we flush the system_wq from rdma_cm context which
    runs from a workqueue context, we can have a circular locking complaint
    [1]. Fix that by using a private workqueue for queue deletion.
    
    [1]:
    ======================================================
    WARNING: possible circular locking dependency detected
    4.19.0-rc4-dbg+ #3 Not tainted
    ------------------------------------------------------
    kworker/5:0/39 is trying to acquire lock:
    00000000a10b6db9 (&id_priv->handler_mutex){+.+.}, at: rdma_destroy_id+0x6f/0x440 [rdma_cm]
    
    but task is already holding lock:
    00000000331b4e2c ((work_completion)(&queue->release_work)){+.+.}, at: process_one_work+0x3ed/0xa20
    
    which lock already depends on the new lock.
    
    the existing dependency chain (in reverse order) is:
    
    -> #3 ((work_completion)(&queue->release_work)){+.+.}:
           process_one_work+0x474/0xa20
           worker_thread+0x63/0x5a0
           kthread+0x1cf/0x1f0
           ret_from_fork+0x24/0x30
    
    -> #2 ((wq_completion)"events"){+.+.}:
           flush_workqueue+0xf3/0x970
           nvmet_rdma_cm_handler+0x133d/0x1734 [nvmet_rdma]
           cma_ib_req_handler+0x72f/0xf90 [rdma_cm]
           cm_process_work+0x2e/0x110 [ib_cm]
           cm_req_handler+0x135b/0x1c30 [ib_cm]
           cm_work_handler+0x2b7/0x38cd [ib_cm]
           process_one_work+0x4ae/0xa20
    nvmet_rdma:nvmet_rdma_cm_handler: nvmet_rdma: disconnected (10): status 0 id 0000000040357082
           worker_thread+0x63/0x5a0
           kthread+0x1cf/0x1f0
           ret_from_fork+0x24/0x30
    nvme nvme0: Reconnecting in 10 seconds...
    
    -> #1 (&id_priv->handler_mutex/1){+.+.}:
           __mutex_lock+0xfe/0xbe0
           mutex_lock_nested+0x1b/0x20
           cma_ib_req_handler+0x6aa/0xf90 [rdma_cm]
           cm_process_work+0x2e/0x110 [ib_cm]
           cm_req_handler+0x135b/0x1c30 [ib_cm]
           cm_work_handler+0x2b7/0x38cd [ib_cm]
           process_one_work+0x4ae/0xa20
           worker_thread+0x63/0x5a0
           kthread+0x1cf/0x1f0
           ret_from_fork+0x24/0x30
    
    -> #0 (&id_priv->handler_mutex){+.+.}:
           lock_acquire+0xc5/0x200
           __mutex_lock+0xfe/0xbe0
           mutex_lock_nested+0x1b/0x20
           rdma_destroy_id+0x6f/0x440 [rdma_cm]
           nvmet_rdma_release_queue_work+0x8e/0x1b0 [nvmet_rdma]
           process_one_work+0x4ae/0xa20
           worker_thread+0x63/0x5a0
           kthread+0x1cf/0x1f0
           ret_from_fork+0x24/0x30
    
    Fixes: 777dc823
    
     ("nvmet-rdma: occasionally flush ongoing controller teardown")
    Reported-by: default avatarBart Van Assche <bvanassche@acm.org>
    Signed-off-by: default avatarSagi Grimberg <sagi@grimberg.me>
    Tested-by: default avatarBart Van Assche <bvanassche@acm.org>
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    2acf70ad