Re: [PATCH v3 2/2] smb: client: prevent premature discard of requests if reconnecting

[Enzo Matsumiya <ematsumiya@suse.de>]

On 10/06, Paulo Alcantara wrote:
>Note that there's currently no backoff mechanism in either CIFS or
>netfslib for writeback, meaning that the write requests will be retried
>forever if the server goes offline.  You'll end up with tasks hanging
>forever on close or fsync.  Trying to fix that in the reconnect path
>doesn't seem the right way to do it, IMO.

Btw, I forgot perhaps the most important bit here -- whenever there's
a reconnect during a write, the file gets corrupted.

That's regardless of how long the downtime was.  As soon as the first
task times out in cifs_wait_for_server_reconnect(), returning
-EHOSTDOWN, that request is lost, and data is corrupted.

Note that the writes (operations) _are_ resumed, but what was lost,
stays lost.

Again, I agree that retrying indefinitely might be wrong, but so is
corrupting data due to a short network outage.

I did try to relieve this situation with this patch, and TBH, after
reassessing it, I fail to see how/where this could be handled in netfs
or cifs I/O path.

The closest I got to a PoC was by loosening the restrictions to set
NETFS_SREQ_NEED_RETRY on smb2_writev_callback() and smb2_async_writev(),
and then we're obviously back to the retry-forever-but-no-corruption
dilemma.


Cheers,

Enzo