linux-kernel - Re: [PATCH] Fix suspicious RCU usage in nfs_idmap_get

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Message-ID: <7960.1475595914@warthog.procyon.org.uk>
Date:   Tue, 04 Oct 2016 16:45:14 +0100
From:   David Howells <dhowells@...hat.com>
To:     Artem Savkov <asavkov@...hat.com>
Cc:     dhowells@...hat.com, linux-nfs@...r.kernel.org,
        trond.myklebust@...marydata.com, anna.schumaker@...app.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix suspicious RCU usage in nfs_idmap_get_key.

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

> nfs_idmap_get_key doesn't hold rkey->sem when calling user_key_payload
> resulting in a "suspicious RCU usage" lockdep splat. It does, however hold
> rcu_read_lock, so it either needs to use unprotected rcu_dereference, or take
> rkey->sem instead of rcu_read_lock.

This shouldn't be using rkey->sem.  user_key_payload() should do sufficient
RCU magic that rcu_read_lock() is sufficient.  Can you please include the RCU
splat?  It's possible user_key_payload() is wrong.

David