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From: Cornelia Huck <cohuck@redhat.com>
To: Parav Pandit <parav@mellanox.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	kwankhede@nvidia.com, alex.williamson@redhat.com,
	cjia@nvidia.com
Subject: Re: [PATCHv3 2/3] vfio/mdev: Avoid creating sysfs remove file on stale device removal
Date: Wed, 22 May 2019 11:55:04 +0200	[thread overview]
Message-ID: <20190522115504.2c440245.cohuck@redhat.com> (raw)
In-Reply-To: <20190516233034.16407-3-parav@mellanox.com>

On Thu, 16 May 2019 18:30:33 -0500
Parav Pandit <parav@mellanox.com> wrote:

> If device is removal is initiated by two threads as below, mdev core
> attempts to create a syfs remove file on stale device.
> During this flow, below [1] call trace is observed.
> 
>      cpu-0                                    cpu-1
>      -----                                    -----
>   mdev_unregister_device()
>     device_for_each_child
>        mdev_device_remove_cb
>           mdev_device_remove
>                                        user_syscall
>                                          remove_store()
>                                            mdev_device_remove()
>                                         [..]
>    unregister device();
>                                        /* not found in list or
>                                         * active=false.
>                                         */
>                                           sysfs_create_file()
>                                           ..Call trace
> 
> Now that mdev core follows correct device removal system of the linux
> bus model, remove shouldn't fail in normal cases. If it fails, there is
> no point of creating a stale file or checking for specific error status.
> 
> kernel: WARNING: CPU: 2 PID: 9348 at fs/sysfs/file.c:327
> sysfs_create_file_ns+0x7f/0x90
> kernel: CPU: 2 PID: 9348 Comm: bash Kdump: loaded Not tainted
> 5.1.0-rc6-vdevbus+ #6
> kernel: Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b
> 08/09/2016
> kernel: RIP: 0010:sysfs_create_file_ns+0x7f/0x90
> kernel: Call Trace:
> kernel: remove_store+0xdc/0x100 [mdev]
> kernel: kernfs_fop_write+0x113/0x1a0
> kernel: vfs_write+0xad/0x1b0
> kernel: ksys_write+0x5a/0xe0
> kernel: do_syscall_64+0x5a/0x210
> kernel: entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Signed-off-by: Parav Pandit <parav@mellanox.com>
> ---
>  drivers/vfio/mdev/mdev_sysfs.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c
> index 9f774b91d275..ffa3dcebf201 100644
> --- a/drivers/vfio/mdev/mdev_sysfs.c
> +++ b/drivers/vfio/mdev/mdev_sysfs.c
> @@ -237,10 +237,8 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
>  		int ret;
>  
>  		ret = mdev_device_remove(dev);
> -		if (ret) {
> -			device_create_file(dev, attr);
> +		if (ret)
>  			return ret;
> -		}
>  	}
>  
>  	return count;

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

  reply	other threads:[~2019-05-22  9:55 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16 23:30 [PATCHv3 0/3] vfio/mdev: Improve vfio/mdev core module Parav Pandit
2019-05-16 23:30 ` [PATCHv3 1/3] vfio/mdev: Improve the create/remove sequence Parav Pandit
2019-05-20 19:54   ` Parav Pandit
2019-05-22  9:57     ` Cornelia Huck
2019-05-22  9:54   ` Cornelia Huck
2019-05-24 18:45     ` Parav Pandit
2019-05-16 23:30 ` [PATCHv3 2/3] vfio/mdev: Avoid creating sysfs remove file on stale device removal Parav Pandit
2019-05-22  9:55   ` Cornelia Huck [this message]
2019-05-16 23:30 ` [PATCHv3 3/3] vfio/mdev: Synchronize device create/remove with parent removal Parav Pandit
2019-05-17 11:22   ` Cornelia Huck
2019-05-17 14:18     ` Parav Pandit
2019-05-20 11:29       ` Cornelia Huck
2019-05-20 19:15         ` Parav Pandit
2019-05-20 22:12           ` Alex Williamson
2019-05-24  9:11             ` Parav Pandit

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