linux-kernel - Re: [GIT PULL] overlay filesystem v25

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20141028041127.GM5718@linux.vnet.ibm.com>
Date:	Mon, 27 Oct 2014 21:11:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-unionfs@...r.kernel.org
Subject: Re: [GIT PULL] overlay filesystem v25

On Tue, Oct 28, 2014 at 01:12:14AM +0000, Al Viro wrote:
> On Mon, Oct 27, 2014 at 10:36:21AM -0700, Paul E. McKenney wrote:
> > Code making direct use of smp_read_barrier_depends() is harder to read,
> > in my experience, but good point on the sparse noise.  Maybe a new
> > lockless_dereference() primitive?  Maybe something like the following?
> > (Untested, probably does not even build.)
> > 
> > #define lockless_dereference(p) \
> > ({ \
> > 	typeof(*p) *_________p1 = ACCESS_ONCE(p); \
> > 	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
> > 	_________p1; \
> > })
> 
> Hmm...  Where would you prefer to put it?  rcupdate.h?

Good a place as any, I guess.  Please see patch below.  Left to myself,
I would send this along for the next merge window, but please let me
know if you would like it sooner.

							Thanx, Paul

------------------------------------------------------------------------

rcu: Provide counterpart to rcu_dereference() for non-RCU situations

Although rcu_dereference() and friends can be used in situations where
object lifetimes are being managed by something other than RCU, the
resulting sparse and lockdep-RCU noise can be annoying.  This commit
therefore supplies a lockless_dereference(), which provides the
protection for dereferences without the RCU-related debugging noise.

Reported-by: Al Viro <viro@...IV.linux.org.uk>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9575c2d403b5..ed4f5939a452 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -617,6 +617,21 @@ static inline void rcu_preempt_sleep_check(void)
 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
 
 /**
+ * lockless_dereference() - safely load a pointer for later dereference
+ * @p: The pointer to load
+ *
+ * Similar to rcu_dereference(), but for situations where the pointed-to
+ * object's lifetime is managed by something other than RCU.  That
+ * "something other" might be reference counting or simple immortality.
+ */
+#define lockless_dereference(p) \
+({ \
+	typeof(p) _________p1 = ACCESS_ONCE(p); \
+	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+	(_________p1); \
+})
+
+/**
  * rcu_assign_pointer() - assign to RCU-protected pointer
  * @p: pointer to assign to
  * @v: value to assign (publish)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/