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

[Christoph Hellwig]

On Thu, Mar 28, 2024 at 03:02:54PM +0900, Damien Le Moal wrote:
> But that is the problem: "checking the zone number again" means referencing the
> plug struct again from the lookup context while the last ref drop context is
> freeing the plug. That race can be lost by the lookup context and lead to
> referencing freed memory. So your solution would be OK for pre-allocated plugs
> only.

Not if it is done in the Rcu critical section.

> For kmalloc-ed() plugs, we still need the rcu grace period for free. So we
> can only optimize for the pre-allocated plugs...

Yes, bt it can use kfree_rcu which doesn't need the rcu_head in the
zwplug.