On Thu, Sep 03, 2015 at 03:20:50PM +1000, Paul Mackerras wrote: > From: "Gautham R. Shenoy" <ego@xxxxxxxxxxxxxxxxxx> > > The current dynamic micro-threading code has a race due to which a > secondary thread naps when it is supposed to be running a vcpu. As a > side effect of this, on a guest exit, the primary thread in > kvmppc_wait_for_nap() finds that this secondary thread hasn't cleared > its vcore pointer. This results in "CPU X seems to be stuck!" > warnings. > > The race is possible since the primary thread on exiting the guests > only waits for all the secondaries to clear its vcore pointer. It > subsequently expects the secondary threads to enter nap while it > unsplits the core. A secondary thread which hasn't yet entered the nap > will loop in kvm_no_guest until its vcore pointer and the do_nap flag > are unset. Once the core has been unsplit, a new vcpu thread can grab > the core and set the do_nap flag *before* setting the vcore pointers > of the secondary. As a result, the secondary thread will now enter nap > via kvm_unsplit_nap instead of running the guest vcpu. > > Fix this by setting the do_nap flag after setting the vcore pointer in > the PACA of the secondary in kvmppc_run_core. Also, ensure that a > secondary thread doesn't nap in kvm_unsplit_nap when the vcore pointer > in its PACA struct is set. > > Fixes: b4deba5c41e9 > Signed-off-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx> Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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