Messages in this thread | | | Date | Fri, 12 Nov 2010 15:13:23 +0800 | From | Américo Wang <> | Subject | Re: Kernel rwlock design, Multicore and IGMP |
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On Fri, Nov 12, 2010 at 11:32:59AM +0800, Cypher Wu wrote: >On Thu, Nov 11, 2010 at 11:23 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: >> Le jeudi 11 novembre 2010 à 21:49 +0800, Cypher Wu a écrit : >> >> Hi >> >> CC netdev, since you ask questions about network stuff _and_ rwlock >> >> >>> I'm using TILEPro and its rwlock in kernel is a liitle different than >>> other platforms. It have a priority for write lock that when tried it >>> will block the following read lock even if read lock is hold by >>> others. Its code can be read in Linux Kernel 2.6.36 in >>> arch/tile/lib/spinlock_32.c. >> >> This seems a bug to me. >> >> read_lock() can be nested. We used such a schem in the past in iptables >> (it can re-enter itself), >> and we used instead a spinlock(), but with many discussions with lkml >> and Linus himself if I remember well. >> >It seems not a problem that read_lock() can be nested or not since >rwlock doesn't have 'owner', it's just that should we give >write_lock() a priority than read_lock() since if there have a lot >read_lock()s then they'll starve write_lock(). >We should work out a well defined behavior so all the >platform-dependent raw_rwlock has to design under that principle.
It is a known weakness of rwlock, it is designed like that. :)
The solution is to use RCU or seqlock, but I don't think seqlock is proper for this case you described. So, try RCU lock. -- 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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