tracing: allocate page when needed

Impact: Cleanup

Sometimes, we open trace_pipe_raw, but we don't read(2) it,
we just splice(2) it, thus, the page is not used.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <49D4666B.4010608@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 24b0168..8e189ff 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3277,19 +3277,13 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
 
        info->tr        = &global_trace;
        info->cpu       = cpu;
-       info->spare     = ring_buffer_alloc_read_page(info->tr->buffer);
+       info->spare     = NULL;
        /* Force reading ring buffer for first read */
        info->read      = (unsigned int)-1;
-       if (!info->spare)
-               goto out;
 
        filp->private_data = info;
 
        return nonseekable_open(inode, filp);
-
- out:
-       kfree(info);
-       return -ENOMEM;
 }
 
 static ssize_t
@@ -3304,6 +3298,11 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
        if (!count)
                return 0;
 
+       if (!info->spare)
+               info->spare = ring_buffer_alloc_read_page(info->tr->buffer);
+       if (!info->spare)
+               return -ENOMEM;
+
        /* Do we have previous read data to read? */
        if (info->read < PAGE_SIZE)
                goto read;
@@ -3342,7 +3341,8 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
 {
        struct ftrace_buffer_info *info = file->private_data;
 
-       ring_buffer_free_read_page(info->tr->buffer, info->spare);
+       if (info->spare)
+               ring_buffer_free_read_page(info->tr->buffer, info->spare);
        kfree(info);
 
        return 0;