Merge tag 'trace-v4.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt...

[sfrench/cifs-2.6.git] / kernel / trace / ring_buffer.c

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index d57fede84b3803c15bfa4eb0324bbea50f4bdd10..91874a95060de5de11aa47d3fbddb8c4980a0da8 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2536,61 +2536,29 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
  * The lock and unlock are done within a preempt disable section.
  * The current_context per_cpu variable can only be modified
  * by the current task between lock and unlock. But it can
- * be modified more than once via an interrupt. To pass this
- * information from the lock to the unlock without having to
- * access the 'in_interrupt()' functions again (which do show
- * a bit of overhead in something as critical as function tracing,
- * we use a bitmask trick.
+ * be modified more than once via an interrupt. There are four
+ * different contexts that we need to consider.
  *
- *  bit 0 =  NMI context
- *  bit 1 =  IRQ context
- *  bit 2 =  SoftIRQ context
- *  bit 3 =  normal context.
+ *  Normal context.
+ *  SoftIRQ context
+ *  IRQ context
+ *  NMI context
  *
- * This works because this is the order of contexts that can
- * preempt other contexts. A SoftIRQ never preempts an IRQ
- * context.
- *
- * When the context is determined, the corresponding bit is
- * checked and set (if it was set, then a recursion of that context
- * happened).
- *
- * On unlock, we need to clear this bit. To do so, just subtract
- * 1 from the current_context and AND it to itself.
- *
- * (binary)
- *  101 - 1 = 100
- *  101 & 100 = 100 (clearing bit zero)
- *
- *  1010 - 1 = 1001
- *  1010 & 1001 = 1000 (clearing bit 1)
- *
- * The least significant bit can be cleared this way, and it
- * just so happens that it is the same bit corresponding to
- * the current context.
+ * If for some reason the ring buffer starts to recurse, we
+ * only allow that to happen at most 4 times (one for each
+ * context). If it happens 5 times, then we consider this a
+ * recusive loop and do not let it go further.
  */
 
 static __always_inline int
 trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
 {
-       unsigned int val = cpu_buffer->current_context;
-       int bit;
-
-       if (in_interrupt()) {
-               if (in_nmi())
-                       bit = RB_CTX_NMI;
-               else if (in_irq())
-                       bit = RB_CTX_IRQ;
-               else
-                       bit = RB_CTX_SOFTIRQ;
-       } else
-               bit = RB_CTX_NORMAL;
-
-       if (unlikely(val & (1 << bit)))
+       if (cpu_buffer->current_context >= 4)
                return 1;
 
-       val |= (1 << bit);
-       cpu_buffer->current_context = val;
+       cpu_buffer->current_context++;
+       /* Interrupts must see this update */
+       barrier();
 
        return 0;
 }
@@ -2598,7 +2566,9 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
 static __always_inline void
 trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
 {
-       cpu_buffer->current_context &= cpu_buffer->current_context - 1;
+       /* Don't let the dec leak out */
+       barrier();
+       cpu_buffer->current_context--;
 }
 
 /**