kernel: FS-Cache: Duplicate cookie detected - what is this?

This appears to be working as intended. The Duplicate cookie detected errors are not indicative of a situation that requires action by the sysadmin.

As has been pointed out on the upstream bug report this may well be working as intended https://bugzilla.kernel.org/show_bug.cgi?id=200145#c12 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ec0328e46d6e5d0f17372eb90ab8e333c2ac7ca9

And:

fscache: Maintain a catalogue of allocated cookies Maintain a catalogue of allocated cookies so that cookie collisions can be handled properly. For the moment, this just involves printing a warning and returning a NULL cookie to the caller of fscache_acquire_cookie(), but in future it might make sense to wait for the old cookie to finish being cleaned up.

This requires the cookie key to be stored attached to the cookie so that we still have the key available if the netfs relinquishes the cookie. This is done by an earlier patch.

The catalogue also renders redundant fscache_netfs_list (used for checking for duplicates), so that can be removed.