On Monday, 14 May 2007 09:26, Gautham R Shenoy wrote: > On Mon, May 14, 2007 at 11:48:46AM +0530, Srivatsa Vaddagiri wrote: > > > > The other complication get/put_hotcpu() had was dealing with > > write-followed-by-read lock attempt by the *same* thread (whilst doing > > cpu_down/up). IIRC this was triggered by some callback processing in > > CPU_DEAD > > or CPU_DOWN_PREPARE. > > > > > > cpu_down() > > |- take write lock > > |- CPU_DOWN_PREPARE > > | |- foo() wants a read_lock > > > > Stupid as it sounds, it was really found to be happening! Gautham, do you > > recall who that foo() was? Somebody in cpufreq I guess .. > > IIRC, it was a problem with ondemand. while handling CPU_DEAD, ondemand code > would call destroy_workqueue, which tried flushing the workqueue, which > once upon a time did lock_cpu_hotplug, before Oleg and Andrew cleaned > that up. > > Ofcourse, cpufreq works fine now after Venki's patches which > just nullifies the reference to the policy structure of the cpu to be > removed during the CPU_DOWN_PREPARE by calling __cpufreq_remove_dev > instead of handling it in CPU_DEAD. > > However, as we have discovered, without freezing all the threads, it > is inadvisable to call flush_workqueue from a cpu-hotplug callback > path.
Please see my recent patch at http://lkml.org/lkml/2007/5/14/7 . It's not exactly the same thing, but I think the trick in there might be useful. Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
