Re: [PATCH rdma-rc] RDMA/mlx5: Fix mkey cache possible deadlock on cleanup

[Leon Romanovsky <leon@kernel.org>]

On Wed, Sep 20, 2023 at 12:56:18PM +0300, Leon Romanovsky wrote:
> From: Shay Drory <shayd@nvidia.com>
> 
> Fix the deadlock by refactoring the MR cache cleanup flow to flush the
> workqueue without holding the rb_lock.
> This adds a race between cache cleanup and creation of new entries which
> we solve by denied creation of new entries after cache cleanup started.
> 
> Lockdep:
> WARNING: possible circular locking dependency detected
>  [ 2785.326074 ] 6.2.0-rc6_for_upstream_debug_2023_01_31_14_02 #1 Not tainted
>  [ 2785.339778 ] ------------------------------------------------------
>  [ 2785.340848 ] devlink/53872 is trying to acquire lock:
>  [ 2785.341701 ] ffff888124f8c0c8 ((work_completion)(&(&ent->dwork)->work)){+.+.}-{0:0}, at: __flush_work+0xc8/0x900
>  [ 2785.343403 ]
>  [ 2785.343403 ] but task is already holding lock:
>  [ 2785.344464 ] ffff88817e8f1260 (&dev->cache.rb_lock){+.+.}-{3:3}, at: mlx5_mkey_cache_cleanup+0x77/0x250 [mlx5_ib]
>  [ 2785.346273 ]
>  [ 2785.346273 ] which lock already depends on the new lock.
>  [ 2785.346273 ]
>  [ 2785.347720 ]
>  [ 2785.347720 ] the existing dependency chain (in reverse order) is:
>  [ 2785.349003 ]
>  [ 2785.349003 ] -> #1 (&dev->cache.rb_lock){+.+.}-{3:3}:
>  [ 2785.350160 ]        __mutex_lock+0x14c/0x15c0
>  [ 2785.350962 ]        delayed_cache_work_func+0x2d1/0x610 [mlx5_ib]
>  [ 2785.352044 ]        process_one_work+0x7c2/0x1310
>  [ 2785.352879 ]        worker_thread+0x59d/0xec0
>  [ 2785.353636 ]        kthread+0x28f/0x330
>  [ 2785.354370 ]        ret_from_fork+0x1f/0x30
>  [ 2785.355135 ]
>  [ 2785.355135 ] -> #0 ((work_completion)(&(&ent->dwork)->work)){+.+.}-{0:0}:
>  [ 2785.356515 ]        __lock_acquire+0x2d8a/0x5fe0
>  [ 2785.357349 ]        lock_acquire+0x1c1/0x540
>  [ 2785.358121 ]        __flush_work+0xe8/0x900
>  [ 2785.358852 ]        __cancel_work_timer+0x2c7/0x3f0
>  [ 2785.359711 ]        mlx5_mkey_cache_cleanup+0xfb/0x250 [mlx5_ib]
>  [ 2785.360781 ]        mlx5_ib_stage_pre_ib_reg_umr_cleanup+0x16/0x30 [mlx5_ib]
>  [ 2785.361969 ]        __mlx5_ib_remove+0x68/0x120 [mlx5_ib]
>  [ 2785.362960 ]        mlx5r_remove+0x63/0x80 [mlx5_ib]
>  [ 2785.363870 ]        auxiliary_bus_remove+0x52/0x70
>  [ 2785.364715 ]        device_release_driver_internal+0x3c1/0x600
>  [ 2785.365695 ]        bus_remove_device+0x2a5/0x560
>  [ 2785.366525 ]        device_del+0x492/0xb80
>  [ 2785.367276 ]        mlx5_detach_device+0x1a9/0x360 [mlx5_core]
>  [ 2785.368615 ]        mlx5_unload_one_devl_locked+0x5a/0x110 [mlx5_core]
>  [ 2785.369934 ]        mlx5_devlink_reload_down+0x292/0x580 [mlx5_core]
>  [ 2785.371292 ]        devlink_reload+0x439/0x590
>  [ 2785.372075 ]        devlink_nl_cmd_reload+0xaef/0xff0
>  [ 2785.372973 ]        genl_family_rcv_msg_doit.isra.0+0x1bd/0x290
>  [ 2785.374011 ]        genl_rcv_msg+0x3ca/0x6c0
>  [ 2785.374798 ]        netlink_rcv_skb+0x12c/0x360
>  [ 2785.375612 ]        genl_rcv+0x24/0x40
>  [ 2785.376295 ]        netlink_unicast+0x438/0x710
>  [ 2785.377121 ]        netlink_sendmsg+0x7a1/0xca0
>  [ 2785.377926 ]        sock_sendmsg+0xc5/0x190
>  [ 2785.378668 ]        __sys_sendto+0x1bc/0x290
>  [ 2785.379440 ]        __x64_sys_sendto+0xdc/0x1b0
>  [ 2785.380255 ]        do_syscall_64+0x3d/0x90
>  [ 2785.381031 ]        entry_SYSCALL_64_after_hwframe+0x46/0xb0
>  [ 2785.381967 ]
>  [ 2785.381967 ] other info that might help us debug this:
>  [ 2785.381967 ]
>  [ 2785.383448 ]  Possible unsafe locking scenario:
>  [ 2785.383448 ]
>  [ 2785.384544 ]        CPU0                    CPU1
>  [ 2785.385383 ]        ----                    ----
>  [ 2785.386193 ]   lock(&dev->cache.rb_lock);
>  [ 2785.386940 ]				lock((work_completion)(&(&ent->dwork)->work));
>  [ 2785.388327 ]				lock(&dev->cache.rb_lock);
>  [ 2785.389425 ]   lock((work_completion)(&(&ent->dwork)->work));
>  [ 2785.390414 ]
>  [ 2785.390414 ]  *** DEADLOCK ***
>  [ 2785.390414 ]
>  [ 2785.391579 ] 6 locks held by devlink/53872:
>  [ 2785.392341 ]  #0: ffffffff84c17a50 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40
>  [ 2785.393630 ]  #1: ffff888142280218 (&devlink->lock_key){+.+.}-{3:3}, at: devlink_get_from_attrs_lock+0x12d/0x2d0
>  [ 2785.395324 ]  #2: ffff8881422d3c38 (&dev->lock_key){+.+.}-{3:3}, at: mlx5_unload_one_devl_locked+0x4a/0x110 [mlx5_core]
>  [ 2785.397322 ]  #3: ffffffffa0e59068 (mlx5_intf_mutex){+.+.}-{3:3}, at: mlx5_detach_device+0x60/0x360 [mlx5_core]
>  [ 2785.399231 ]  #4: ffff88810e3cb0e8 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x8d/0x600
>  [ 2785.400864 ]  #5: ffff88817e8f1260 (&dev->cache.rb_lock){+.+.}-{3:3}, at: mlx5_mkey_cache_cleanup+0x77/0x250 [mlx5_ib]
> 
> Fixes: b95845178328 ("RDMA/mlx5: Change the cache structure to an RB-tree")
> Signed-off-by: Shay Drory <shayd@nvidia.com>
> Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/infiniband/hw/mlx5/mlx5_ib.h |  1 +
>  drivers/infiniband/hw/mlx5/mr.c      | 16 ++++++++++++++--
>  2 files changed, 15 insertions(+), 2 deletions(-)

Applied