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>
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1 changed files with 11 additions and 3 deletions
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@ -310,24 +310,32 @@ extern int rcu_my_thread_group_empty(void);
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* (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
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* the future.
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*/
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#ifdef __CHECKER__
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#define rcu_dereference_sparse(p, space) \
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((void)(((typeof(*p) space *)p) == p))
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#else /* #ifdef __CHECKER__ */
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#define rcu_dereference_sparse(p, space)
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#endif /* #else #ifdef __CHECKER__ */
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#define __rcu_access_pointer(p, space) \
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({ \
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typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
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(void) (((typeof (*p) space *)p) == p); \
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rcu_dereference_sparse(p, space); \
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((typeof(*p) __force __kernel *)(_________p1)); \
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})
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#define __rcu_dereference_check(p, c, space) \
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({ \
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typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
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rcu_lockdep_assert(c); \
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(void) (((typeof (*p) space *)p) == p); \
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rcu_dereference_sparse(p, space); \
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smp_read_barrier_depends(); \
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((typeof(*p) __force __kernel *)(_________p1)); \
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})
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#define __rcu_dereference_protected(p, c, space) \
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({ \
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rcu_lockdep_assert(c); \
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(void) (((typeof (*p) space *)p) == p); \
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rcu_dereference_sparse(p, space); \
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((typeof(*p) __force __kernel *)(p)); \
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})
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