On 04/09/2018 04:54 PM, Nikolay Borisov wrote:
On 9.04.2018 11:39, Anand Jain wrote:
On 04/04/2018 02:34 AM, David Sterba wrote:
The volume mutex does not protect against anything in this case, the
comment about scrub is right but not related to locking and looks
confusing. The comment in btrfs_find_device_missing_or_by_path is wrong
and confusing too.
The device_list_mutex is not held here to protect device lookup, but in
this case device replace cannot run in parallel with device removal (due
to exclusive op protection), so we don't need further locking here.
Agreed, usage of device_list_mutex and volume_mutex is kind of redundant.
There are unfinished features in btrfs volume, such as device offline
while it was mounted (patches in the ML).
It's better to replace volume_mutex with device_list_mutex instead of
removing it, as we might need it in the context mentioned above.
Or it's not a good idea to clean up until all the features are in place
otherwise we end up adding the locks again at some point.
It's better that cleanups go so they leave the code in a better shape
than it is. Then when/if the missing features are complete and the
patches that implement them contain proper explanation how locking
works the code can be committed.
Taking into account how there is preparatory code in btrfs for features
which haven't landed for quite some time (i.e the in-band dedup stuff)
I'm against people future-proofing without clear path to merging the
feature the future-proofing pertains to.
Ok. Lets clean it up first.
Thanks, Anand
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