Re: [PATCH 0/7] crypto: switch to static calls for CRC-T10DIF

On Mon, Jan 11, 2021 at 07:36:20PM +0100, Ard Biesheuvel wrote:

On Mon, 11 Jan 2021 at 18:27, Ard Biesheuvel [off-list ref] wrote:

quoted

On Mon, 11 Jan 2021 at 17:52, Ard Biesheuvel [off-list ref] wrote:

quoted

quoted

Special request to Peter to take a look at patch #2, and in particular,
whether synchronize_rcu_tasks() is sufficient to ensure that a module
providing the target of a static call can be unloaded safely.

It seems I may have managed to confuse myself slightly here: without
an upper bound on the size of the input of the crc_t10dif() routine, I
suppose we can never assume that all its callers have finished.

Replying to self again - apologies.

I think this is actually correct after all: synchronize_rcu_tasks()
guarantees that all tasks have passed through a 'safe state', i.e.,
voluntary schedule(), return to userland, etc, which guarantees that
no task could be executing the old static call target after
synchronize_rcu_tasks() returns.

Right, I think it should work.

My initial question was why you'd want to support the unreg at all.
AFAICT these implementations are tiny, why bother having them as a
module, or if you insist having them as a module, why allowing removal?