1 files changed, 23 insertions, 52 deletions

diff --git a/drivers/oprofile/cpu_buffer.c b/drivers/oprofile/cpu_buffer.c
index 7581dbe456da..219f79e2210a 100644
--- a/drivers/oprofile/cpu_buffer.c
+++ b/drivers/oprofile/cpu_buffer.c
@@ -30,23 +30,7 @@
 
 #define OP_BUFFER_FLAGS 0
 
-/*
- * Read and write access is using spin locking. Thus, writing to the
- * buffer by NMI handler (x86) could occur also during critical
- * sections when reading the buffer. To avoid this, there are 2
- * buffers for independent read and write access. Read access is in
- * process context only, write access only in the NMI handler. If the
- * read buffer runs empty, both buffers are swapped atomically. There
- * is potentially a small window during swapping where the buffers are
- * disabled and samples could be lost.
- *
- * Using 2 buffers is a little bit overhead, but the solution is clear
- * and does not require changes in the ring buffer implementation. It
- * can be changed to a single buffer solution when the ring buffer
- * access is implemented as non-locking atomic code.
- */
-static struct ring_buffer *op_ring_buffer_read;
-static struct ring_buffer *op_ring_buffer_write;
+static struct ring_buffer *op_ring_buffer;
 DEFINE_PER_CPU(struct oprofile_cpu_buffer, op_cpu_buffer);
 
 static void wq_sync_buffer(struct work_struct *work);
@@ -68,12 +52,9 @@ void oprofile_cpu_buffer_inc_smpl_lost(void)
 
 void free_cpu_buffers(void)
 {
-        if (op_ring_buffer_read)
-                ring_buffer_free(op_ring_buffer_read);
-        op_ring_buffer_read = NULL;
-        if (op_ring_buffer_write)
-                ring_buffer_free(op_ring_buffer_write);
-        op_ring_buffer_write = NULL;
+        if (op_ring_buffer)
+                ring_buffer_free(op_ring_buffer);
+        op_ring_buffer = NULL;
 }
 
 #define RB_EVENT_HDR_SIZE 4
@@ -86,11 +67,8 @@ int alloc_cpu_buffers(void)
         unsigned long byte_size = buffer_size * (sizeof(struct op_sample) +
                                                  RB_EVENT_HDR_SIZE);
 
-        op_ring_buffer_read = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
-        if (!op_ring_buffer_read)
-                goto fail;
-        op_ring_buffer_write = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
-        if (!op_ring_buffer_write)
+        op_ring_buffer = ring_buffer_alloc(byte_size, OP_BUFFER_FLAGS);
+        if (!op_ring_buffer)
                 goto fail;
 
         for_each_possible_cpu(i) {
@@ -162,16 +140,11 @@ struct op_sample
 *op_cpu_buffer_write_reserve(struct op_entry *entry, unsigned long size)
 {
         entry->event = ring_buffer_lock_reserve
-                (op_ring_buffer_write, sizeof(struct op_sample) +
+                (op_ring_buffer, sizeof(struct op_sample) +
                  size * sizeof(entry->sample->data[0]));
-        if (entry->event)
-                entry->sample = ring_buffer_event_data(entry->event);
-        else
-                entry->sample = NULL;
-
-        if (!entry->sample)
+        if (!entry->event)
                 return NULL;
-
+        entry->sample = ring_buffer_event_data(entry->event);
         entry->size = size;
         entry->data = entry->sample->data;
 
@@ -180,25 +153,16 @@ struct op_sample
 
 int op_cpu_buffer_write_commit(struct op_entry *entry)
 {
-        return ring_buffer_unlock_commit(op_ring_buffer_write, entry->event);
+        return ring_buffer_unlock_commit(op_ring_buffer, entry->event);
 }
 
 struct op_sample *op_cpu_buffer_read_entry(struct op_entry *entry, int cpu)
 {
         struct ring_buffer_event *e;
-        e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL, NULL);
-        if (e)
-                goto event;
-        if (ring_buffer_swap_cpu(op_ring_buffer_read,
-                                 op_ring_buffer_write,
-                                 cpu))
+        e = ring_buffer_consume(op_ring_buffer, cpu, NULL, NULL);
+        if (!e)
                 return NULL;
-        e = ring_buffer_consume(op_ring_buffer_read, cpu, NULL, NULL);
-        if (e)
-                goto event;
-        return NULL;
 
-event:
         entry->event = e;
         entry->sample = ring_buffer_event_data(e);
         entry->size = (ring_buffer_event_length(e) - sizeof(struct op_sample))
@@ -209,8 +173,7 @@ event:
 
 unsigned long op_cpu_buffer_entries(int cpu)
 {
-        return ring_buffer_entries_cpu(op_ring_buffer_read, cpu)
-                + ring_buffer_entries_cpu(op_ring_buffer_write, cpu);
+        return ring_buffer_entries_cpu(op_ring_buffer, cpu);
 }
 
 static int
@@ -356,8 +319,16 @@ void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
 
 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 {
-        int is_kernel = !user_mode(regs);
-        unsigned long pc = profile_pc(regs);
+        int is_kernel;
+        unsigned long pc;
+
+        if (likely(regs)) {
+                is_kernel = !user_mode(regs);
+                pc = profile_pc(regs);
+        } else {
+                is_kernel = 0;    /* This value will not be used */
+                pc = ESCAPE_CODE; /* as this causes an early return. */
+        }
 
         __oprofile_add_ext_sample(pc, regs, event, is_kernel);
 }