Subject: Re: [PATCH] rxrpc_find_service_conn_rcu: use read_seqbegin() rather than read_seqbegin_or_lock()

From: Al Viro <[email-masked]>
Date: Wed, 1 Nov 2023 22:48:55 +0000

On Wed, Nov 01, 2023 at 10:52:15PM +0100, Oleg Nesterov wrote:

> > Why would you want to force that "switch to locked on the second pass" policy
> > on every possible caller?
> 
> Because this is what (I think) read_seqbegin_or_lock() is supposed to do.
> It should take the lock for writing if the lockless access failed. At least
> according to the documentation.

Not really - it's literally seqbegin or lock, depending upon what the caller
tells it...  IMO the mistake in docs is the insistence on using do-while
loop for its users.

Take a look at d_walk() and try to shoehorn that into your variant.  Especially
the D_WALK_NORETRY handling...