From: Cornelia Huck <cohuck@redhat.com>
To: Parav Pandit <parav@mellanox.com>
Cc: alex.williamson@redhat.com, davem@davemloft.net,
kvm@vger.kernel.org, netdev@vger.kernel.org, saeedm@mellanox.com,
kwankhede@nvidia.com, leon@kernel.org, jiri@mellanox.com,
linux-rdma@vger.kernel.org
Subject: Re: [PATCH net-next 11/19] vfio/mdev: Improvise mdev life cycle and parent removal scheme
Date: Fri, 8 Nov 2019 14:01:10 +0100 [thread overview]
Message-ID: <20191108140110.6f24916b.cohuck@redhat.com> (raw)
In-Reply-To: <20191107160834.21087-11-parav@mellanox.com>
On Thu, 7 Nov 2019 10:08:26 -0600
Parav Pandit <parav@mellanox.com> wrote:
I guess that should be s/Improvise/improve/ in $SUBJECT, no?
> mdev creation and removal sequence synchronization with parent device
> removal is improved in [1].
>
> However such improvement using semaphore either limiting or leads to
> complex locking scheme when used across multiple subsystem such as mdev
> and devlink.
>
> When mdev devices are used with devlink eswitch device, following
> deadlock sequence can be witnessed.
>
> mlx5_core 0000:06:00.0: E-Switch: Disable: mode(OFFLOADS), nvfs(4), active vports(5)
> mlx5_core 0000:06:00.0: MDEV: Unregistering
>
> WARNING: possible circular locking dependency detected
> ------------------------------------------------------
> devlink/42094 is trying to acquire lock:
> 00000000eb6fb4c7 (&parent->unreg_sem){++++}, at: mdev_unregister_device+0xf1/0x160 [mdev]
> 012but task is already holding lock:
> 00000000efcd208e (devlink_mutex){+.+.}, at: devlink_nl_pre_doit+0x1d/0x170
> 012which lock already depends on the new lock.
> 012the existing dependency chain (in reverse order) is:
> 012-> #1 (devlink_mutex){+.+.}:
> lock_acquire+0xbd/0x1a0
> __mutex_lock+0x84/0x8b0
> devlink_unregister+0x17/0x60
> mlx5_sf_unload+0x21/0x60 [mlx5_core]
> mdev_remove+0x1e/0x40 [mdev]
> device_release_driver_internal+0xdc/0x1a0
> bus_remove_device+0xef/0x160
> device_del+0x163/0x360
> mdev_device_remove_common+0x1e/0xa0 [mdev]
> mdev_device_remove+0x8d/0xd0 [mdev]
> remove_store+0x71/0x90 [mdev]
> kernfs_fop_write+0x113/0x1a0
> vfs_write+0xad/0x1b0
> ksys_write+0x5c/0xd0
> do_syscall_64+0x5a/0x270
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 012-> #0 (&parent->unreg_sem){++++}:
> check_prev_add+0xb0/0x810
> __lock_acquire+0xd4b/0x1090
> lock_acquire+0xbd/0x1a0
> down_write+0x33/0x70
> mdev_unregister_device+0xf1/0x160 [mdev]
> esw_offloads_disable+0xe/0x70 [mlx5_core]
> mlx5_eswitch_disable+0x149/0x190 [mlx5_core]
> mlx5_devlink_eswitch_mode_set+0xd0/0x180 [mlx5_core]
> devlink_nl_cmd_eswitch_set_doit+0x3e/0xb0
> genl_family_rcv_msg+0x3a2/0x420
> genl_rcv_msg+0x47/0x90
> netlink_rcv_skb+0xc9/0x100
> genl_rcv+0x24/0x40
> netlink_unicast+0x179/0x220
> netlink_sendmsg+0x2f6/0x3f0
> sock_sendmsg+0x30/0x40
> __sys_sendto+0xdc/0x160
> __x64_sys_sendto+0x24/0x30
> do_syscall_64+0x5a/0x270
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> Possible unsafe locking scenario:
> CPU0 CPU1
> ---- ----
> lock(devlink_mutex);
> lock(&parent->unreg_sem);
> lock(devlink_mutex);
> lock(&parent->unreg_sem);
> 012 *** DEADLOCK ***
> 3 locks held by devlink/42094:
> 0: 0000000097a0c4aa (cb_lock){++++}, at: genl_rcv+0x15/0x40
> 1: 00000000baf61ad2 (genl_mutex){+.+.}, at: genl_rcv_msg+0x66/0x90
> 2: 00000000efcd208e (devlink_mutex){+.+.}, at: devlink_nl_pre_doit+0x1d/0x170
>
> To summarize,
> mdev_remove()
> read locks -> unreg_sem [ lock-A ]
> [..]
> devlink_unregister();
> mutex lock devlink_mutex [ lock-B ]
>
> devlink eswitch->switchdev-legacy mode change.
> devlink_nl_cmd_eswitch_set_doit()
> mutex lock devlink_mutex [ lock-B ]
> mdev_unregister_device()
> write locks -> unreg_sem [ lock-A]
So, this problem starts to pop up once you hook up that devlink stuff
with the mdev stuff, and previous users of mdev just did not have a
locking scheme similar to devlink?
>
> Hence, instead of using semaphore, such synchronization is achieved
> using srcu which is more flexible that eliminates nested locking.
>
> SRCU based solution is already proposed before at [2].
>
> [1] commit 5715c4dd66a3 ("vfio/mdev: Synchronize device create/remove with parent removal")
> [2] https://lore.kernel.org/patchwork/patch/1055254/
I don't quite recall the discussion there... is this a rework of a
patch you proposed before? Confused.
>
> Signed-off-by: Parav Pandit <parav@mellanox.com>
> ---
> drivers/vfio/mdev/mdev_core.c | 56 +++++++++++++++++++++++---------
> drivers/vfio/mdev/mdev_private.h | 3 +-
> 2 files changed, 43 insertions(+), 16 deletions(-)
(...)
> @@ -207,6 +207,7 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> dev_warn(dev, "Failed to create compatibility class link\n");
>
> list_add(&parent->next, &parent_list);
> + rcu_assign_pointer(parent->self, parent);
> mutex_unlock(&parent_list_lock);
>
> dev_info(dev, "MDEV: Registered\n");
> @@ -250,14 +251,29 @@ void mdev_unregister_device(struct device *dev)
> list_del(&parent->next);
> mutex_unlock(&parent_list_lock);
>
> - down_write(&parent->unreg_sem);
> + /*
> + * Publish that this mdev parent is unregistering. So any new
> + * create/remove cannot start on this parent anymore by user.
> + */
> + rcu_assign_pointer(parent->self, NULL);
> +
> + /*
> + * Wait for any active create() or remove() mdev ops on the parent
> + * to complete.
> + */
> + synchronize_srcu(&parent->unreg_srcu);
> +
> + /*
> + * At this point it is confirmed that any pending user initiated
> + * create or remove callbacks accessing the parent are completed.
> + * It is safe to remove the parent now.
> + */
So, you're putting an srcu-handled self reference there and use that as
an indication whether the parent is unregistering?
>
> class_compat_remove_link(mdev_bus_compat_class, dev, NULL);
>
> device_for_each_child(dev, NULL, mdev_device_remove_cb);
>
> parent_remove_sysfs_files(parent);
> - up_write(&parent->unreg_sem);
>
> mdev_put_parent(parent);
>
next prev parent reply other threads:[~2019-11-08 13:01 UTC|newest]
Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-07 16:04 [PATCH net-next 00/19] Mellanox, mlx5 sub function support Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 01/19] net/mlx5: E-switch, Move devlink port close to eswitch port Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 02/19] net/mlx5: E-Switch, Add SF vport, vport-rep support Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 03/19] net/mlx5: Introduce SF table framework Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 04/19] net/mlx5: Introduce SF life cycle APIs to allocate/free Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 05/19] net/mlx5: E-Switch, Enable/disable SF's vport during SF life cycle Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 06/19] net/mlx5: Add support for mediated devices in switchdev mode Parav Pandit
2019-11-08 10:32 ` Jiri Pirko
2019-11-08 16:03 ` Parav Pandit
2019-11-08 16:22 ` Jiri Pirko
2019-11-08 16:29 ` Parav Pandit
2019-11-08 18:01 ` Jiri Pirko
2019-11-08 18:04 ` Jiri Pirko
2019-11-08 18:21 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 07/19] vfio/mdev: Introduce sha1 based mdev alias Parav Pandit
2019-11-08 11:04 ` Jiri Pirko
2019-11-08 15:59 ` Parav Pandit
2019-11-08 16:28 ` Jiri Pirko
2019-11-08 11:10 ` Cornelia Huck
2019-11-08 16:03 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 08/19] vfio/mdev: Make mdev alias unique among all mdevs Parav Pandit
2019-11-08 10:49 ` Jiri Pirko
2019-11-08 15:13 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 09/19] vfio/mdev: Expose mdev alias in sysfs tree Parav Pandit
2019-11-08 13:22 ` Jiri Pirko
2019-11-08 18:03 ` Alex Williamson
2019-11-08 18:16 ` Jiri Pirko
2019-11-07 16:08 ` [PATCH net-next 10/19] vfio/mdev: Introduce an API mdev_alias Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 11/19] vfio/mdev: Improvise mdev life cycle and parent removal scheme Parav Pandit
2019-11-08 13:01 ` Cornelia Huck [this message]
2019-11-08 16:12 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 12/19] devlink: Introduce mdev port flavour Parav Pandit
2019-11-07 20:38 ` Jakub Kicinski
2019-11-07 21:03 ` Parav Pandit
2019-11-08 1:17 ` Jakub Kicinski
2019-11-08 1:44 ` Parav Pandit
2019-11-08 2:20 ` Jakub Kicinski
2019-11-08 2:31 ` Parav Pandit
2019-11-08 9:46 ` Jiri Pirko
2019-11-08 15:45 ` Parav Pandit
2019-11-08 16:31 ` Jiri Pirko
2019-11-08 16:43 ` Parav Pandit
2019-11-08 18:11 ` Jiri Pirko
2019-11-08 18:23 ` Parav Pandit
2019-11-08 18:34 ` Jiri Pirko
2019-11-08 18:56 ` Parav Pandit
2019-11-08 9:30 ` Jiri Pirko
2019-11-08 15:41 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 13/19] net/mlx5: Register SF devlink port Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 14/19] net/mlx5: Share irqs between SFs and parent PCI device Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 15/19] net/mlx5: Add load/unload routines for SF driver binding Parav Pandit
2019-11-08 9:48 ` Jiri Pirko
2019-11-08 11:13 ` Jiri Pirko
2019-11-07 16:08 ` [PATCH net-next 16/19] net/mlx5: Implement dma ops and params for mediated device Parav Pandit
2019-11-07 20:42 ` Jakub Kicinski
2019-11-07 21:30 ` Parav Pandit
2019-11-08 1:16 ` Jakub Kicinski
2019-11-08 6:37 ` Christoph Hellwig
2019-11-08 15:29 ` Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 17/19] net/mlx5: Add mdev driver to bind to mdev devices Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 18/19] Documentation: net: mlx5: Add mdev usage documentation Parav Pandit
2019-11-07 16:08 ` [PATCH net-next 19/19] mtty: Optionally support mtty alias Parav Pandit
2019-11-08 6:26 ` Leon Romanovsky
2019-11-08 10:45 ` Jiri Pirko
2019-11-08 15:08 ` Parav Pandit
2019-11-08 15:15 ` Jiri Pirko
2019-11-08 13:46 ` Cornelia Huck
2019-11-08 15:10 ` Parav Pandit
2019-11-08 15:28 ` Cornelia Huck
2019-11-08 15:30 ` Parav Pandit
2019-11-08 17:54 ` Alex Williamson
2019-11-08 9:51 ` [PATCH net-next 01/19] net/mlx5: E-switch, Move devlink port close to eswitch port Jiri Pirko
2019-11-08 15:50 ` Parav Pandit
2019-11-07 17:03 ` [PATCH net-next 00/19] Mellanox, mlx5 sub function support Leon Romanovsky
2019-11-07 20:10 ` Parav Pandit
2019-11-08 6:20 ` Leon Romanovsky
2019-11-08 15:01 ` Parav Pandit
2019-11-07 20:32 ` Jakub Kicinski
2019-11-07 20:52 ` Parav Pandit
2019-11-08 1:16 ` Jakub Kicinski
2019-11-08 1:49 ` Parav Pandit
2019-11-08 2:12 ` Jakub Kicinski
2019-11-08 12:12 ` Jiri Pirko
2019-11-08 14:40 ` Jason Gunthorpe
2019-11-08 15:40 ` Parav Pandit
2019-11-08 19:12 ` Jakub Kicinski
2019-11-08 20:12 ` Jason Gunthorpe
2019-11-08 20:20 ` Parav Pandit
2019-11-08 20:32 ` Jason Gunthorpe
2019-11-08 20:52 ` gregkh
2019-11-08 20:34 ` Alex Williamson
2019-11-08 21:05 ` Jason Gunthorpe
2019-11-08 21:19 ` gregkh
2019-11-08 21:52 ` Alex Williamson
2019-11-08 22:48 ` Parav Pandit
2019-11-09 0:57 ` Jason Gunthorpe
2019-11-09 17:41 ` Jakub Kicinski
2019-11-10 19:04 ` Jason Gunthorpe
2019-11-10 19:48 ` Parav Pandit
2019-11-11 14:17 ` Jiri Pirko
2019-11-11 14:58 ` Parav Pandit
2019-11-11 15:06 ` Jiri Pirko
2019-11-19 4:51 ` Parav Pandit
2019-11-09 0:12 ` Jason Gunthorpe
2019-11-09 0:45 ` Parav Pandit
2019-11-11 2:19 ` Jason Wang
2019-11-08 21:45 ` Jakub Kicinski
2019-11-09 0:44 ` Jason Gunthorpe
2019-11-09 8:46 ` gregkh
2019-11-09 11:18 ` Jiri Pirko
2019-11-09 17:28 ` Jakub Kicinski
2019-11-10 9:16 ` gregkh
2019-11-09 17:27 ` Jakub Kicinski
2019-11-10 9:18 ` gregkh
2019-11-11 3:46 ` Jakub Kicinski
2019-11-11 5:18 ` Parav Pandit
2019-11-11 13:30 ` Jiri Pirko
2019-11-11 14:14 ` gregkh
2019-11-11 14:37 ` Jiri Pirko
2019-11-10 19:37 ` Jason Gunthorpe
2019-11-11 3:57 ` Jakub Kicinski
2019-11-08 16:06 ` Parav Pandit
2019-11-08 19:06 ` Jakub Kicinski
2019-11-08 19:34 ` Parav Pandit
2019-11-08 19:48 ` Jakub Kicinski
2019-11-08 19:41 ` Jiri Pirko
2019-11-08 20:40 ` Parav Pandit
2019-11-08 21:21 ` Jakub Kicinski
2019-11-08 21:39 ` Jiri Pirko
2019-11-08 21:51 ` Jakub Kicinski
2019-11-08 22:21 ` Jiri Pirko
2019-11-07 23:57 ` David Miller
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