[PATCH v3 09/30] block: Pre-allocate zone write plugs

[Christoph Hellwig]

On Thu, Mar 28, 2024 at 03:33:13PM +0900, Damien Le Moal wrote:
> Ha. OK. I did not see that one. But that means that the plug kfree() can then
> block the caller. Given that the last ref drop may happen from BIO completion
> context (when the last write to a zone making the zone full complete), I do not
> think we can use this function...

Ah, damn.  So yes, we probably still need the rcu head.  We can kill
the gendisk pointer, though.  Or just stick with the existing version
and don't bother with the micro-optimization, at which point the
mempool might actually be the simpler implementation?