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| author | Peter Zijlstra <peterz@infradead.org> | 2015-05-27 04:39:36 +0300 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2015-05-28 05:02:05 +0300 |
| commit | 0a04b0166929405cd833c1cc40f99e862b965ddc (patch) | |
| tree | c108e2aee50ce533cef248c755e86d48c59a4ebf /include/linux/compiler.h | |
| parent | 6695b92a60bc7160c92d6dc5b17cc79673017c2f (diff) | |
| download | linux-0a04b0166929405cd833c1cc40f99e862b965ddc.tar.xz | |
rcu: Move lockless_dereference() out of rcupdate.h
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>
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 867722591be2..eae42c21d5fd 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -457,6 +457,21 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s (volatile typeof(x) *)&(x); }) #define ACCESS_ONCE(x) (*__ACCESS_ONCE(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"))) |