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Message-Id: <1191784307.3618.8.camel@localhost.localdomain> Date: Mon, 08 Oct 2007 03:11:47 +0800 From: Jun WANG <junwang1234@...il.com> To: penguin-kernel@...ove.sakura.ne.jp Cc: linux-kernel@...r.kernel.org Subject: Re:Sleeping in RCU list traversal Hi >Something like this? > >rcu_read_lock(); >list_for_each_rcu(p, ...) { > ptr = list_entry(p, struct ..., list); > /* Grab a reference to "ptr". */ > rcu_read_unlock(); > my_task_that_may_sleep(ptr); > rcu_read_lock(); > /* Drop a reference to "ptr". */ >} >rcu_read_unlock(); >Regarding my case, memory region pointed by "ptr" never be removed. >Do I need to grab a reference to "ptr" ? In Document/RCU/whatisRCU.txt Note that the value returned by rcu_dereference() is valid only within the enclosing RCU read-side critical section. For example, the following is -not- legal: rcu_read_lock(); p = rcu_dereference(head.next); rcu_read_unlock(); x = p->address; rcu_read_lock(); y = p->data; rcu_read_unlock(); Holding a reference from one RCU read-side critical section to another is just as illegal as holding a reference from one lock-based critical section to another! Similarly, using a reference outside of the critical section in which it was acquired is just as illegal as doing so with normal locking. Jun Wang - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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