On Tue, Jan 22, 2013 at 01:10:51PM +0530, Srivatsa S. Bhat wrote:
> Once stop_machine() is gone from the CPU offline path, we won't be able to
> depend on preempt_disable() or local_irq_disable() to prevent CPUs from
> going offline from under us.
>
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
> while invoking from atomic context.
>
> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
Weird. I see this in the patch but I don't see it in the header? Did you
explicitly suppress the CC part?
Anyhow, the patch looks sane enough, thought I need to to run it through
a test framework just to be on a sure side.
> Cc: Jeremy Fitzhardinge <jer...@goop.org>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: x...@kernel.org
> Cc: xen-de...@lists.xensource.com
> Cc: virtualizat...@lists.linux-foundation.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
> ---
>
> arch/x86/xen/mmu.c | 11 +++++++++--
> arch/x86/xen/smp.c | 9 +++++++++
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 01de35c..6a95a15 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -39,6 +39,7 @@
> * Jeremy Fitzhardinge <jer...@xensource.com>, XenSource Inc, 2007
> */
> #include <linux/sched.h>
> +#include <linux/cpu.h>
> #include <linux/highmem.h>
> #include <linux/debugfs.h>
> #include <linux/bug.h>
> @@ -1163,9 +1164,13 @@ static void xen_drop_mm_ref(struct mm_struct *mm)
> */
> static void xen_exit_mmap(struct mm_struct *mm)
> {
> - get_cpu(); /* make sure we don't move around */
> + /*
> + * Make sure we don't move around, and prevent CPUs from going
> + * offline.
> + */
> + get_online_cpus_atomic();
> xen_drop_mm_ref(mm);
> - put_cpu();
> + put_online_cpus_atomic();
>
> spin_lock(&mm->page_table_lock);
>
> @@ -1371,6 +1376,7 @@ static void xen_flush_tlb_others(const struct cpumask
> *cpus,
> args->op.arg2.vcpumask = to_cpumask(args->mask);
>
> /* Remove us, and any offline CPUS. */
> + get_online_cpus_atomic();
> cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
> cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
>
> @@ -1383,6 +1389,7 @@ static void xen_flush_tlb_others(const struct cpumask
> *cpus,
> MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);
>
> xen_mc_issue(PARAVIRT_LAZY_MMU);
> + put_online_cpus_atomic();
> }
>
> static unsigned long xen_read_cr3(void)
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 4f7d259..7d753ae 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -16,6 +16,7 @@
> #include <linux/err.h>
> #include <linux/slab.h>
> #include <linux/smp.h>
> +#include <linux/cpu.h>
> #include <linux/irq_work.h>
>
> #include <asm/paravirt.h>
> @@ -487,8 +488,10 @@ static void __xen_send_IPI_mask(const struct cpumask
> *mask,
> {
> unsigned cpu;
>
> + get_online_cpus_atomic();
> for_each_cpu_and(cpu, mask, cpu_online_mask)
> xen_send_IPI_one(cpu, vector);
> + put_online_cpus_atomic();
> }
>
> static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
> @@ -551,8 +554,10 @@ void xen_send_IPI_all(int vector)
> {
> int xen_vector = xen_map_vector(vector);
>
> + get_online_cpus_atomic();
> if (xen_vector >= 0)
> __xen_send_IPI_mask(cpu_online_mask, xen_vector);
> + put_online_cpus_atomic();
> }
>
> void xen_send_IPI_self(int vector)
> @@ -572,20 +577,24 @@ void xen_send_IPI_mask_allbutself(const struct cpumask
> *mask,
> if (!(num_online_cpus() > 1))
> return;
>
> + get_online_cpus_atomic();
> for_each_cpu_and(cpu, mask, cpu_online_mask) {
> if (this_cpu == cpu)
> continue;
>
> xen_smp_send_call_function_single_ipi(cpu);
> }
> + put_online_cpus_atomic();
> }
>
> void xen_send_IPI_allbutself(int vector)
> {
> int xen_vector = xen_map_vector(vector);
>
> + get_online_cpus_atomic();
> if (xen_vector >= 0)
> xen_send_IPI_mask_allbutself(cpu_online_mask, xen_vector);
> + put_online_cpus_atomic();
> }
>
> static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
>
> --
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