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Jarek Poplawski wrote: > On 18-09-2007 16:55, Nadia Derbey wrote: > ... > >>Well, reviewing the code I found another place where the >>rcu_read_unlock() was missing. >>I'm so sorry for the inconvenience. It's true that I should have tested >>with CONFIG_PREEMPT=y :-( >>Now, the ltp tests pass even with this option set... >> >>In attachment you'll find a patch thhat >>1) adds the missing rcu_read_unlock() >>2) replaces Andrew's fix with a new one: the rcu_read_lock() is now >>taken in ipc_lock() / ipc_lock_by_ptr() and released in ipc_unlock(), >>exactly as it was done in the ref code. > > > BTW, probably I miss something, but I wonder, how this RCU is working > here. E.g. in msg.c do_msgsnd() there is: > > msq = msg_lock_check(ns, msqid); > ... > > msg_unlock(msq); > schedule(); > > ipc_lock_by_ptr(&msq->q_perm); > > Since msq_lock_check() gets msq with ipc_lock_check() under > rcu_read_lock(), and then goes msg_unlock(msq) (i.e. ipc_unlock()) > with rcu_read_unlock(), is it valid to use this with > ipc_lock_by_ptr() yet? Before Calling msg_unlock() they call ipc_rcu_getref() that increments a refcount in the rcu header for the msg structure. This guarantees that the the structure won't be freed before they relock it. Once the structure is relocked by ipc_lock_by_ptr(), they do the symmetric operation i.e. ipc_rcu_putref(). Regards, Nadia - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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