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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-09-13 17:24:21 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-09-23 09:15:01 -0700 |
| commit | 53ecfba259f54b6967a35d19f4a564e3bc07997f (patch) | |
| tree | eaaeebe2a38abe1a401a0d2d40181abaefa80d48 /include/linux/rcupdate.h | |
| parent | 829f8ed2c963df7c23d1c644db6c4387eb1601fa (diff) | |
| download | lwn-53ecfba259f54b6967a35d19f4a564e3bc07997f.tar.gz lwn-53ecfba259f54b6967a35d19f4a564e3bc07997f.zip | |
rcu: only one evaluation of arg in rcu_dereference_check() unless sparse
The current version of the __rcu_access_pointer(), __rcu_dereference_check(),
and __rcu_dereference_protected() macros evaluate their "p" argument
three times, not counting typeof()s. This is bad news if that argument
contains a side effect. This commit therefore evaluates this argument
only once in normal kernel builds. However, the straightforward approach
defeats sparse's RCU-pointer checking, so when __CHECKER__ is defined,
the additional pair of evaluations of the "p" argument are performed in
order to permit sparse to detect misuse of RCU-protected pointers.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 89414d67d961..03cda7bed985 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -310,24 +310,32 @@ extern int rcu_my_thread_group_empty(void); * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in * the future. */ + +#ifdef __CHECKER__ +#define rcu_dereference_sparse(p, space) \ + ((void)(((typeof(*p) space *)p) == p)) +#else /* #ifdef __CHECKER__ */ +#define rcu_dereference_sparse(p, space) +#endif /* #else #ifdef __CHECKER__ */ + #define __rcu_access_pointer(p, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_check(p, c, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ rcu_lockdep_assert(c); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ smp_read_barrier_depends(); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_protected(p, c, space) \ ({ \ rcu_lockdep_assert(c); \ - (void) (((typeof (*p) space *)p) == p); \ + rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(p)); \ }) |