[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] On netfront accelerator add/remove watches
Neil Turton wrote: Hi, BVK Chaitanya wrote:I see that netfront_accel_add_watch and netfront_accel_remove_watch functions are _not_ protected by accelerator_mutex in accel.c Is there any specific reason for this?Yes. These functions need to be synchronised by the callers. Adding a mutex here would ensure that they didn't execute at the same time, but wouldn't impose any order on the calls. This matters because add followed by remove is different from remove followed by add. The callers need to decide which order they should be executed in. So the watch is only added/removed from a xenbus callback. I think these callbacks should be synchronised by xenbus. Can someone confirm that? OK. I understand it now. I see that they sometimes get called twice (and result in BUG_ON) in very fast (20ms) domain suspend-resume cycles and I couldn't figure out how it is possible :-(Is that the BUG_ON in netfront_accelerator_add_watch? One possible explanation is that suspend_cancel is called and then otherend_changed is called. Can you add a printk to netfront_suspend_cancel to see if it gets called just before the BUG_ON gets triggered? Yes, BUG_ON was from netfront_accelerator_add_watch function. I think i got the problem: xen_suspend which calls suspend_cancel is not serialized properly. Under heavy load and very fine suspend-resume cycles, multiple suspend_cancel instances can be running simultaneously. regards, -- bvk-chaitanya _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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