| From | Luis Henriques <> | Subject | [PATCH 3.16.y-ckt 098/130] rcu: Move lockless_dereference() out of rcupdate.h | Date | Fri, 4 Sep 2015 14:08:06 +0100 |
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3.16.7-ckt17 -stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra <peterz@infradead.org>
commit 0a04b0166929405cd833c1cc40f99e862b965ddc upstream.
I want to use lockless_dereference() from seqlock.h, which would mean including rcupdate.h from it, however rcupdate.h already includes seqlock.h.
Avoid this by moving lockless_dereference() into compiler.h. This is somewhat tricky since it uses smp_read_barrier_depends() which isn't available there, but its a CPP macro so we can get away with it.
The alternative would be moving it into asm/barrier.h, but that would be updating each arch (I can do if people feel that is more appropriate).
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> [ luis: 3.16 prereq for: 37868fe113ff "x86/ldt: Make modify_ldt synchronous" ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- include/linux/compiler.h | 15 +++++++++++++++ include/linux/rcupdate.h | 15 --------------- 2 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index d5ad7b1118fc..da293bf86575 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -380,6 +380,21 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); */ #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +/** + * 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); \ +}) + /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */ #ifdef CONFIG_KPROBES # define __kprobes __attribute__((__section__(".kprobes.text"))) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 53ea8bed34bc..6a94cc8b1ca0 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -593,21 +593,6 @@ 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)
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