Re: [PATCH 04/11] btrfs: reada: use sprout device_list_mutex

[Nikolay Borisov <nborisov@suse.com>]

On 30.08.20 г. 17:40 ч., Anand Jain wrote:
> On an fs mounted using a sprout-device, the seed fs_devices are maintained
> in a linked list under fs_info->fs_devices. Each seed's fs_devices also
> have device_list_mutex initialized to protect against the potential race
> with delete threads. But the delete thread (at btrfs_rm_device()) is holding
> the fs_info::fs_devices::device_list_mutex mutex which is sprout's
> device_list_mutex instead of seed's device_list_mutex. Moreover, there
> aren't any significient benefits in using the seed::device_list_mutex
> instead of sprout::device_list_mutex.
> 
> So this patch converts them of using the seed::device_list_mutex to
> sprout::device_list_mutex.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>

nit: I'm beginning to think that the structure representing seed devices
shouldn't be a full-fledged btrfs_fs_devices but a slimmed down version
which contains only the necessary bits.


Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/reada.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
> index c0035fc0ec67..9b54a51ba860 100644
> --- a/fs/btrfs/reada.c
> +++ b/fs/btrfs/reada.c
> @@ -776,13 +776,11 @@ static int __reada_start_for_fsdevs(struct btrfs_fs_devices *fs_devices)
>  
>  	do {
>  		enqueued = 0;
> -		mutex_lock(&fs_devices->device_list_mutex);
>  		list_for_each_entry(device, &fs_devices->devices, dev_list) {
>  			if (atomic_read(&device->reada_in_flight) <
>  			    MAX_IN_FLIGHT)
>  				enqueued += reada_start_machine_dev(device);
>  		}
> -		mutex_unlock(&fs_devices->device_list_mutex);
>  		total += enqueued;
>  	} while (enqueued && total < 10000);
>  
> @@ -795,10 +793,13 @@ static void __reada_start_machine(struct btrfs_fs_info *fs_info)
>  	int i;
>  	u64 enqueued = 0;
>  
> +	mutex_lock(&fs_devices->device_list_mutex);
> +
>  	enqueued += __reada_start_for_fsdevs(fs_devices);
>  	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list)
>  		enqueued += __reada_start_for_fsdevs(seed_devs);
>  
> +	mutex_unlock(&fs_devices->device_list_mutex);
>  	if (enqueued == 0)
>  		return;
>  
>