3 files changed, 55 insertions, 26 deletions

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 8d85046adcc8..9670e70139fd 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -29,6 +29,7 @@
 #include <linux/kallsyms.h>
 #include <linux/random.h>
 #include <linux/prctl.h>
+#include <linux/nmi.h>
 
 #include <asm/asm.h>
 #include <asm/bootinfo.h>
@@ -655,28 +656,42 @@ unsigned long arch_align_stack(unsigned long sp)
         return sp & ALMASK;
 }
 
-static void arch_dump_stack(void *info)
+static DEFINE_PER_CPU(call_single_data_t, backtrace_csd);
+static struct cpumask backtrace_csd_busy;
+
+static void handle_backtrace(void *info)
 {
-        struct pt_regs *regs;
+        nmi_cpu_backtrace(get_irq_regs());
+        cpumask_clear_cpu(smp_processor_id(), &backtrace_csd_busy);
+}
 
-        regs = get_irq_regs();
+static void raise_backtrace(cpumask_t *mask)
+{
+        call_single_data_t *csd;
+        int cpu;
 
-        if (regs)
-                show_regs(regs);
+        for_each_cpu(cpu, mask) {
+                /*
+                 * If we previously sent an IPI to the target CPU & it hasn't
+                 * cleared its bit in the busy cpumask then it didn't handle
+                 * our previous IPI & it's not safe for us to reuse the
+                 * call_single_data_t.
+                 */
+                if (cpumask_test_and_set_cpu(cpu, &backtrace_csd_busy)) {
+                        pr_warn("Unable to send backtrace IPI to CPU%u - perhaps it hung?\n",
+                                cpu);
+                        continue;
+                }
 
-        dump_stack();
+                csd = &per_cpu(backtrace_csd, cpu);
+                csd->func = handle_backtrace;
+                smp_call_function_single_async(cpu, csd);
+        }
 }
 
 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
 {
-        long this_cpu = get_cpu();
-
-        if (cpumask_test_cpu(this_cpu, mask) && !exclude_self)
-                dump_stack();
-
-        smp_call_function_many(mask, arch_dump_stack, NULL, 1);
-
-        put_cpu();
+        nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace);
 }
 
 int mips_get_process_fp_mode(struct task_struct *task)
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index d67fa74622ee..8d505a21396e 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -351,6 +351,7 @@ static void __show_regs(const struct pt_regs *regs)
 void show_regs(struct pt_regs *regs)
 {
         __show_regs((struct pt_regs *)regs);
+        dump_stack();
 }
 
 void show_registers(struct pt_regs *regs)
diff --git a/arch/mips/mm/ioremap.c b/arch/mips/mm/ioremap.c
index 1986e09fb457..1601d90b087b 100644
--- a/arch/mips/mm/ioremap.c
+++ b/arch/mips/mm/ioremap.c
@@ -9,6 +9,7 @@
 #include <linux/export.h>
 #include <asm/addrspace.h>
 #include <asm/byteorder.h>
+#include <linux/ioport.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -98,6 +99,20 @@ static int remap_area_pages(unsigned long address, phys_addr_t phys_addr,
         return error;
 }
 
+static int __ioremap_check_ram(unsigned long start_pfn, unsigned long nr_pages,
+                               void *arg)
+{
+        unsigned long i;
+
+        for (i = 0; i < nr_pages; i++) {
+                if (pfn_valid(start_pfn + i) &&
+                    !PageReserved(pfn_to_page(start_pfn + i)))
+                        return 1;
+        }
+
+        return 0;
+}
+
 /*
  * Generic mapping function (not visible outside):
  */
@@ -116,8 +131,8 @@ static int remap_area_pages(unsigned long address, phys_addr_t phys_addr,
 
 void __iomem * __ioremap(phys_addr_t phys_addr, phys_addr_t size, unsigned long flags)
 {
+        unsigned long offset, pfn, last_pfn;
         struct vm_struct * area;
-        unsigned long offset;
         phys_addr_t last_addr;
         void * addr;
 
@@ -137,18 +152,16 @@ void __iomem * __ioremap(phys_addr_t phys_addr, phys_addr_t size, unsigned long
                 return (void __iomem *) CKSEG1ADDR(phys_addr);
 
         /*
-         * Don't allow anybody to remap normal RAM that we're using..
+         * Don't allow anybody to remap RAM that may be allocated by the page
+         * allocator, since that could lead to races & data clobbering.
          */
-        if (phys_addr < virt_to_phys(high_memory)) {
-                char *t_addr, *t_end;
-                struct page *page;
-
-                t_addr = __va(phys_addr);
-                t_end = t_addr + (size - 1);
-
-                for(page = virt_to_page(t_addr); page <= virt_to_page(t_end); page++)
-                        if(!PageReserved(page))
-                                return NULL;
+        pfn = PFN_DOWN(phys_addr);
+        last_pfn = PFN_DOWN(last_addr);
+        if (walk_system_ram_range(pfn, last_pfn - pfn + 1, NULL,
+                                  __ioremap_check_ram) == 1) {
+                WARN_ONCE(1, "ioremap on RAM at %pa - %pa\n",
+                          &phys_addr, &last_addr);
+                return NULL;
         }
 
         /*