[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Problems with spin_lock_irqsave() and for_each_online_cpu()
On 17/10/2013 20:34, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote: > As for the spinlocks, while I as the programmer am fairly sure that > "&per_cpu(t_lock, i)" is unlikely to change, coverity takes into account > that updates to __per_cpu_offset[i] have no protection. Because of > RELOC_HIDE(), gcc can't hoist the per_cpu() calculation, but will run > from register cached values of per_cpu__t_lock and __per_cpu_offset[i], > so is guaranteed to find the same lock both times even if > __per_cpu_offset[i] changes. > > However, it occurs to me that there is no protection between > for_each_online_cpu() finding a bit set in the cpu_online_map and safely > using per_cpu() to poke at another cpus data. One solution seems to be > to make use of {get,put}_cpu_maps() but this seems overkill especially > as the innards of a for_each_online_cpu() loop only care about one > particular pcpu not disappearing under its feet. CPUs are taken offline in a stop_machine_run environment, *and* the __per_cpu_offset[i] change is done via RCU. We're safe here I'm sure. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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