From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Triplett Subject: Re: [PATCH tip/core/rcu 09/12] fs: Substitute rcu_access_pointer() for rcu_dereference_raw() Date: Mon, 17 Feb 2014 14:00:15 -0800 Message-ID: <20140217220014.GH7941@thin> References: <20140217213533.GA5387@linux.vnet.ibm.com> <1392672959-6386-1-git-send-email-paulmck@linux.vnet.ibm.com> <1392672959-6386-9-git-send-email-paulmck@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu, Alexander Viro , linux-fsdevel@vger.kernel.org To: "Paul E. McKenney" Return-path: Content-Disposition: inline In-Reply-To: <1392672959-6386-9-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Feb 17, 2014 at 01:35:56PM -0800, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > (Trivial patch.) > > If the code is looking at the RCU-protected pointer itself, but not > dereferencing it, the rcu_dereference() functions can be downgraded to > rcu_access_pointer(). This commit makes this downgrade in __alloc_fd(), > which simply compares the RCU-protected pointer against NULL with no > dereferencing. > > Signed-off-by: Paul E. McKenney > Cc: Alexander Viro > Cc: linux-fsdevel@vger.kernel.org I'm beginning to wonder if this common pattern ought to have an rcu_pointer_is_null(), which would not return the pointer, only the boolean. Regardless, for this patch: Reviewed-by: Josh Triplett > fs/file.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/file.c b/fs/file.c > index db25c2bdfe46..18f7d27855c4 100644 > --- a/fs/file.c > +++ b/fs/file.c > @@ -497,7 +497,7 @@ repeat: > error = fd; > #if 1 > /* Sanity check */ > - if (rcu_dereference_raw(fdt->fd[fd]) != NULL) { > + if (rcu_access_pointer(fdt->fd[fd]) != NULL) { > printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd); > rcu_assign_pointer(fdt->fd[fd], NULL); > } > -- > 1.8.1.5 >