Re: [PATCH] btrfs: ratelimit device path change info on mounted device

[David Sterba <dsterba@suse.cz>]

On Tue, Jul 16, 2019 at 09:59:10PM +0800, Anand Jain wrote:
> If there are more than one path to a device, the last scanned path
> will map to the mounted FS. In some Linux based os there appears to be a
> system script (autofs?) which fails to notice that a device's alternative
> path is already mounted, and so the change in device-path gets logged
> every ~2mins whenever such a script is active.
> 
> kernel: [33017.407252] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/mapper/cryptdata4tb--vg-backup new:/dev/dm-13
> kernel: [33017.522242] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/dm-13 new:/dev/mapper/cryptdata4tb--vg-backup
> kernel: [33018.797161] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/mapper/cryptdata4tb--vg-backup new:/dev/dm-13
> kernel: [33019.061631] BTRFS info (device sdc3):
> device fsid 4d1ba5af-8b89-4cb5-96c6-55d1f028a202 devid 4 moved
> old:/dev/dm-13 new:/dev/mapper/cryptdata4tb--vg-backup
> 
> Fix this by using the ratelimit printk.

The ratelimiting will most certainly not stop the repeated messages,
btrfs_info_rl_in_rcu uses the default settings which is to limit within
5 seconds and allow burts of 10 messages.