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author | David Howells <dhowells@redhat.com> | 2010-04-09 15:39:11 -0700 |
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committer | Ingo Molnar <mingo@elte.hu> | 2010-04-14 12:20:04 +0200 |
commit | c08c68dd76bd6b776bc0eb45a5e8f354ed772cdf (patch) | |
tree | 5324c73474b1e73631392de814e8ecebd5956d5b /include/linux/rcupdate.h | |
parent | b62730baea32f86fe91a7930e4b7ee8d82778b79 (diff) | |
download | kernel_samsung_espresso10-c08c68dd76bd6b776bc0eb45a5e8f354ed772cdf.zip kernel_samsung_espresso10-c08c68dd76bd6b776bc0eb45a5e8f354ed772cdf.tar.gz kernel_samsung_espresso10-c08c68dd76bd6b776bc0eb45a5e8f354ed772cdf.tar.bz2 |
rcu: Better explain the condition parameter of rcu_dereference_check()
Better explain the condition parameter of
rcu_dereference_check() that describes the conditions under
which the dereference is permitted to take place (and
incorporate Yong Zhang's suggestion). This condition is only
checked under lockdep proving.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: eric.dumazet@gmail.com
LKML-Reference: <1270852752-25278-2-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r-- | include/linux/rcupdate.h | 28 |
1 files changed, 23 insertions, 5 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 8fe8660..9f1ddfe 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -195,12 +195,30 @@ static inline int rcu_read_lock_sched_held(void) /** * rcu_dereference_check - rcu_dereference with debug checking + * @p: The pointer to read, prior to dereferencing + * @c: The conditions under which the dereference will take place * - * Do an rcu_dereference(), but check that the context is correct. - * For example, rcu_dereference_check(gp, rcu_read_lock_held()) to - * ensure that the rcu_dereference_check() executes within an RCU - * read-side critical section. It is also possible to check for - * locks being held, for example, by using lockdep_is_held(). + * Do an rcu_dereference(), but check that the conditions under which the + * dereference will take place are correct. Typically the conditions indicate + * the various locking conditions that should be held at that point. The check + * should return true if the conditions are satisfied. + * + * For example: + * + * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || + * lockdep_is_held(&foo->lock)); + * + * could be used to indicate to lockdep that foo->bar may only be dereferenced + * if either the RCU read lock is held, or that the lock required to replace + * the bar struct at foo->bar is held. + * + * Note that the list of conditions may also include indications of when a lock + * need not be held, for example during initialisation or destruction of the + * target struct: + * + * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || + * lockdep_is_held(&foo->lock) || + * atomic_read(&foo->usage) == 0); */ #define rcu_dereference_check(p, c) \ ({ \ |