diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-10-27 21:11:27 -0700 |
|---|---|---|
| committer | Luis Henriques <luis.henriques@canonical.com> | 2015-08-31 14:37:39 +0100 |
| commit | 4903dc9f830525b03f6c86ed6563489453feb00f (patch) | |
| tree | 220c3b105741f60522fdda02f7828343420b6f67 /include/linux | |
| parent | 2cf3a79d7d586a3d770ec10ce3045fe13cfae28a (diff) | |
rcu: Provide counterpart to rcu_dereference() for non-RCU situations
commit 54ef6df3f3f1353d99c80c437259d317b2cd1cbd upstream.
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@ZenIV.linux.org.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[ luis: 3.16 prereq for:
37868fe113ff "x86/ldt: Make modify_ldt synchronous" ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/rcupdate.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6a94cc8b1ca0..53ea8bed34bc 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -593,6 +593,21 @@ 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) |