[MIPS] SMTC: Fix recursion in instant IPI replay code.

local_irq_restore -> raw_local_irq_restore -> irq_restore_epilog ->
	smtc_ipi_replay -> smtc_ipi_dq -> spin_unlock_irqrestore ->
	_spin_unlock_irqrestore -> local_irq_restore

The recursion does abort when there is no more IPI queued for a CPU, so
this isn't usually fatal which is why we got away with this for so long
until this was discovered by code inspection.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

3 files changed, 69 insertions, 42 deletions

diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index e50fe20571f..5dcfab6b288 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -999,10 +999,17 @@ static void setup_cross_vpe_interrupts(unsigned int nvpe)
 
 /*
  * SMTC-specific hacks invoked from elsewhere in the kernel.
+ *
+ * smtc_ipi_replay is called from raw_local_irq_restore which is only ever
+ * called with interrupts disabled.  We do rely on interrupts being disabled
+ * here because using spin_lock_irqsave()/spin_unlock_irqrestore() would
+ * result in a recursive call to raw_local_irq_restore().
  */
 
-void smtc_ipi_replay(void)
+static void __smtc_ipi_replay(void)
 {
+        unsigned int cpu = smp_processor_id();
+
         /*
          * To the extent that we've ever turned interrupts off,
          * we may have accumulated deferred IPIs.  This is subtle.
@@ -1017,17 +1024,30 @@ void smtc_ipi_replay(void)
          * is clear, and we'll handle it as a real pseudo-interrupt
          * and not a pseudo-pseudo interrupt.
          */
-        if (IPIQ[smp_processor_id()].depth > 0) {
-                struct smtc_ipi *pipi;
-                extern void self_ipi(struct smtc_ipi *);
+        if (IPIQ[cpu].depth > 0) {
+                while (1) {
+                        struct smtc_ipi_q *q = &IPIQ[cpu];
+                        struct smtc_ipi *pipi;
+                        extern void self_ipi(struct smtc_ipi *);
+
+                        spin_lock(&q->lock);
+                        pipi = __smtc_ipi_dq(q);
+                        spin_unlock(&q->lock);
+                        if (!pipi)
+                                break;
 
-                while ((pipi = smtc_ipi_dq(&IPIQ[smp_processor_id()]))) {
                         self_ipi(pipi);
-                        smtc_cpu_stats[smp_processor_id()].selfipis++;
+                        smtc_cpu_stats[cpu].selfipis++;
                 }
         }
 }
 
+void smtc_ipi_replay(void)
+{
+        raw_local_irq_disable();
+        __smtc_ipi_replay();
+}
+
 EXPORT_SYMBOL(smtc_ipi_replay);
 
 void smtc_idle_loop_hook(void)
@@ -1132,7 +1152,13 @@ void smtc_idle_loop_hook(void)
          * is in use, there should never be any.
          */
 #ifndef CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY
-        smtc_ipi_replay();
+        {
+                unsigned long flags;
+
+                local_irq_save(flags);
+                __smtc_ipi_replay();
+                local_irq_restore(flags);
+        }
 #endif /* CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY */
 }
 
diff --git a/include/asm-mips/irqflags.h b/include/asm-mips/irqflags.h
index af3b07dfad4..e459fa05db8 100644
--- a/include/asm-mips/irqflags.h
+++ b/include/asm-mips/irqflags.h
@@ -13,29 +13,9 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/compiler.h>
 #include <asm/hazards.h>
 
-/*
- * CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY does prompt replay of deferred IPIs,
- * at the cost of branch and call overhead on each local_irq_restore()
- */
-
-#ifdef CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY
-
-extern void smtc_ipi_replay(void);
-
-#define irq_restore_epilog(flags)                               \
-do {                                                            \
-        if (!(flags & 0x0400))                                  \
-                smtc_ipi_replay();                              \
-} while (0)
-
-#else
-
-#define irq_restore_epilog(ignore) do { } while (0)
-
-#endif /* CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY */
-
 __asm__ (
         "       .macro  raw_local_irq_enable                            \n"
         "       .set    push                                            \n"
@@ -205,17 +185,28 @@ __asm__ (
         "       .set    pop                                             \n"
         "       .endm                                                   \n");
 
-#define raw_local_irq_restore(flags)                                    \
-do {                                                                    \
-        unsigned long __tmp1;                                           \
-                                                                        \
-        __asm__ __volatile__(                                           \
-                "raw_local_irq_restore\t%0"                             \
-                : "=r" (__tmp1)                                         \
-                : "0" (flags)                                           \
-                : "memory");                                            \
-        irq_restore_epilog(flags);                                      \
-} while(0)
+extern void smtc_ipi_replay(void);
+
+static inline void raw_local_irq_restore(unsigned long flags)
+{
+        unsigned long __tmp1;
+
+#ifdef CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY
+        /*
+         * CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY does prompt replay of deferred
+         * IPIs, at the cost of branch and call overhead on each
+         * local_irq_restore()
+         */
+        if (unlikely(!(flags & 0x0400)))
+                smtc_ipi_replay();
+#endif
+
+        __asm__ __volatile__(
+                "raw_local_irq_restore\t%0"
+                : "=r" (__tmp1)
+                : "0" (flags)
+                : "memory");
+}
 
 static inline int raw_irqs_disabled_flags(unsigned long flags)
 {
diff --git a/include/asm-mips/smtc_ipi.h b/include/asm-mips/smtc_ipi.h
index 360ea6d250c..a52a4a7a36e 100644
--- a/include/asm-mips/smtc_ipi.h
+++ b/include/asm-mips/smtc_ipi.h
@@ -65,12 +65,10 @@ static inline void smtc_ipi_nq(struct smtc_ipi_q *q, struct smtc_ipi *p)
         spin_unlock_irqrestore(&q->lock, flags);
 }
 
-static inline struct smtc_ipi *smtc_ipi_dq(struct smtc_ipi_q *q)
+static inline struct smtc_ipi *__smtc_ipi_dq(struct smtc_ipi_q *q)
 {
         struct smtc_ipi *p;
-        long flags;
 
-        spin_lock_irqsave(&q->lock, flags);
         if (q->head == NULL)
                 p = NULL;
         else {
@@ -81,7 +79,19 @@ static inline struct smtc_ipi *smtc_ipi_dq(struct smtc_ipi_q *q)
                 if (q->head == NULL)
                         q->tail = NULL;
         }
+
+        return p;
+}
+
+static inline struct smtc_ipi *smtc_ipi_dq(struct smtc_ipi_q *q)
+{
+        unsigned long flags;
+        struct smtc_ipi *p;
+
+        spin_lock_irqsave(&q->lock, flags);
+        p = __smtc_ipi_dq(q);
         spin_unlock_irqrestore(&q->lock, flags);
+
         return p;
 }