powerpc/perf_event: Fix oops due to perf_event_do_pending call

Anton Blanchard found that large POWER systems would occasionally
crash in the exception exit path when profiling with perf_events.
The symptom was that an interrupt would occur late in the exit path
when the MSR[RI] (recoverable interrupt) bit was clear.  Interrupts
should be hard-disabled at this point but they were enabled.  Because
the interrupt was not recoverable the system panicked.

The reason is that the exception exit path was calling
perf_event_do_pending after hard-disabling interrupts, and
perf_event_do_pending will re-enable interrupts.

The simplest and cleanest fix for this is to use the same mechanism
that 32-bit powerpc does, namely to cause a self-IPI by setting the
decrementer to 1.  This means we can remove the tests in the exception
exit path and raw_local_irq_restore.

This also makes sure that the call to perf_event_do_pending from
timer_interrupt() happens within irq_enter/irq_exit.  (Note that
calling perf_event_do_pending from timer_interrupt does not mean that
there is a possible 1/HZ latency; setting the decrementer to 1 ensures
that the timer interrupt will happen immediately, i.e. within one
timebase tick, which is a few nanoseconds or 10s of nanoseconds.)

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: stable@kernel.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

4 files changed, 48 insertions, 28 deletions

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 957ceb7059c5..c09138d150d4 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -133,7 +133,6 @@ int main(void)
         DEFINE(PACAKMSR, offsetof(struct paca_struct, kernel_msr));
         DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));
         DEFINE(PACAHARDIRQEN, offsetof(struct paca_struct, hard_enabled));
-        DEFINE(PACAPERFPEND, offsetof(struct paca_struct, perf_event_pending));
         DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));
 #ifdef CONFIG_PPC_MM_SLICES
         DEFINE(PACALOWSLICESPSIZE, offsetof(struct paca_struct,
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 07109d843787..42e9d908914a 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -556,15 +556,6 @@ ALT_FW_FTR_SECTION_END_IFCLR(FW_FEATURE_ISERIES)
 2:
         TRACE_AND_RESTORE_IRQ(r5);
 
-#ifdef CONFIG_PERF_EVENTS
-        /* check paca->perf_event_pending if we're enabling ints */
-        lbz     r3,PACAPERFPEND(r13)
-        and.    r3,r3,r5
-        beq     27f
-        bl      .perf_event_do_pending
-27:
-#endif /* CONFIG_PERF_EVENTS */
-
         /* extract EE bit and use it to restore paca->hard_enabled */
         ld      r3,_MSR(r1)
         rldicl  r4,r3,49,63             /* r0 = (r3 >> 15) & 1 */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 64f6f2031c22..066bd31551d5 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -53,7 +53,6 @@
 #include <linux/bootmem.h>
 #include <linux/pci.h>
 #include <linux/debugfs.h>
-#include <linux/perf_event.h>
 
 #include <asm/uaccess.h>
 #include <asm/system.h>
@@ -145,11 +144,6 @@ notrace void raw_local_irq_restore(unsigned long en)
         }
 #endif /* CONFIG_PPC_STD_MMU_64 */
 
-        if (test_perf_event_pending()) {
-                clear_perf_event_pending();
-                perf_event_do_pending();
-        }
-
         /*
          * if (get_paca()->hard_enabled) return;
          * But again we need to take care that gcc gets hard_enabled directly
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 1b16b9a3e49a..0441bbdadbd1 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -532,25 +532,60 @@ void __init iSeries_time_init_early(void)
 }
 #endif /* CONFIG_PPC_ISERIES */
 
-#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_PPC32)
-DEFINE_PER_CPU(u8, perf_event_pending);
+#ifdef CONFIG_PERF_EVENTS
 
-void set_perf_event_pending(void)
+/*
+ * 64-bit uses a byte in the PACA, 32-bit uses a per-cpu variable...
+ */
+#ifdef CONFIG_PPC64
+static inline unsigned long test_perf_event_pending(void)
 {
-        get_cpu_var(perf_event_pending) = 1;
-        set_dec(1);
-        put_cpu_var(perf_event_pending);
+        unsigned long x;
+
+        asm volatile("lbz %0,%1(13)"
+                : "=r" (x)
+                : "i" (offsetof(struct paca_struct, perf_event_pending)));
+        return x;
 }
 
+static inline void set_perf_event_pending_flag(void)
+{
+        asm volatile("stb %0,%1(13)" : :
+                "r" (1),
+                "i" (offsetof(struct paca_struct, perf_event_pending)));
+}
+
+static inline void clear_perf_event_pending(void)
+{
+        asm volatile("stb %0,%1(13)" : :
+                "r" (0),
+                "i" (offsetof(struct paca_struct, perf_event_pending)));
+}
+
+#else /* 32-bit */
+
+DEFINE_PER_CPU(u8, perf_event_pending);
+
+#define set_perf_event_pending_flag()   __get_cpu_var(perf_event_pending) = 1
 #define test_perf_event_pending()       __get_cpu_var(perf_event_pending)
 #define clear_perf_event_pending()      __get_cpu_var(perf_event_pending) = 0
 
-#else  /* CONFIG_PERF_EVENTS && CONFIG_PPC32 */
+#endif /* 32 vs 64 bit */
+
+void set_perf_event_pending(void)
+{
+        preempt_disable();
+        set_perf_event_pending_flag();
+        set_dec(1);
+        preempt_enable();
+}
+
+#else  /* CONFIG_PERF_EVENTS */
 
 #define test_perf_event_pending()       0
 #define clear_perf_event_pending()
 
-#endif /* CONFIG_PERF_EVENTS && CONFIG_PPC32 */
+#endif /* CONFIG_PERF_EVENTS */
 
 /*
  * For iSeries shared processors, we have to let the hypervisor
@@ -582,10 +617,6 @@ void timer_interrupt(struct pt_regs * regs)
         set_dec(DECREMENTER_MAX);
 
 #ifdef CONFIG_PPC32
-        if (test_perf_event_pending()) {
-                clear_perf_event_pending();
-                perf_event_do_pending();
-        }
         if (atomic_read(&ppc_n_lost_interrupts) != 0)
                 do_IRQ(regs);
 #endif
@@ -604,6 +635,11 @@ void timer_interrupt(struct pt_regs * regs)
 
         calculate_steal_time();
 
+        if (test_perf_event_pending()) {
+                clear_perf_event_pending();
+                perf_event_do_pending();
+        }
+
 #ifdef CONFIG_PPC_ISERIES
         if (firmware_has_feature(FW_FEATURE_ISERIES))
                 get_lppaca()->int_dword.fields.decr_int = 0;