Merge branch 'perfcounters-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perfcounters-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (60 commits)
  perf tools: Avoid unnecessary work in directory lookups
  perf stat: Clean up statistics calculations a bit more
  perf stat: More advanced variance computation
  perf stat: Use stddev_mean in stead of stddev
  perf stat: Remove the limit on repeat
  perf stat: Change noise calculation to use stddev
  x86, perf_counter, bts: Do not allow kernel BTS tracing for now
  x86, perf_counter, bts: Correct pointer-to-u64 casts
  x86, perf_counter, bts: Fail if BTS is not available
  perf_counter: Fix output-sharing error path
  perf trace: Fix read_string()
  perf trace: Print out in nanoseconds
  perf tools: Seek to the end of the header area
  perf trace: Fix parsing of perf.data
  perf trace: Sample timestamps as well
  perf_counter: Introduce new (non-)paranoia level to allow raw tracepoint access
  perf trace: Sample the CPU too
  perf tools: Work around strict aliasing related warnings
  perf tools: Clean up warnings list in the Makefile
  perf tools: Complete support for dynamic strings
  ...

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/powerpc/mm/stab.c b/arch/powerpc/mm/stab.c
index 98cd1dc2ae75..ab5fb48b3e90 100644
--- a/arch/powerpc/mm/stab.c
+++ b/arch/powerpc/mm/stab.c
@@ -164,7 +164,7 @@ void switch_stab(struct task_struct *tsk, struct mm_struct *mm)
 {
         struct stab_entry *stab = (struct stab_entry *) get_paca()->stab_addr;
         struct stab_entry *ste;
-        unsigned long offset = __get_cpu_var(stab_cache_ptr);
+        unsigned long offset;
         unsigned long pc = KSTK_EIP(tsk);
         unsigned long stack = KSTK_ESP(tsk);
         unsigned long unmapped_base;
@@ -172,6 +172,15 @@ void switch_stab(struct task_struct *tsk, struct mm_struct *mm)
         /* Force previous translations to complete. DRENG */
         asm volatile("isync" : : : "memory");
 
+        /*
+         * We need interrupts hard-disabled here, not just soft-disabled,
+         * so that a PMU interrupt can't occur, which might try to access
+         * user memory (to get a stack trace) and possible cause an STAB miss
+         * which would update the stab_cache/stab_cache_ptr per-cpu variables.
+         */
+        hard_irq_disable();
+
+        offset = __get_cpu_var(stab_cache_ptr);
         if (offset <= NR_STAB_CACHE_ENTRIES) {
                 int i;