linux-kernel - Re: [PATCH] Use proper lock in fscache_objlist

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Message-ID: <7737.1475595811@warthog.procyon.org.uk>
Date:   Tue, 04 Oct 2016 16:43:31 +0100
From:   David Howells <dhowells@...hat.com>
To:     Artem Savkov <asavkov@...hat.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Use proper lock in fscache_objlist_config.

Artem Savkov <asavkov@...hat.com> wrote:

> fscache_objlist_config doesn't hold rkey->sem when calling user_key_payload,
> that can result in a "suspicious RCU usage" warning. It does hold
> rcu_read_lock,  so it either needs to use unprotected rcu_dereference,
> or take rkey->sem instead of rcu_read_lock.

It shouldn't take key->sem.  The RCU lock should be necessary as
user_key_payload() wraps a call to rcu_dereference().

Did you encounter a lockdep report or did you visually inspect this?

David