tracing: fix splice return too large

I got these from strace:

 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 12288
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 16384
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192
 splice(0x3, 0, 0x5, 0, 0x1000, 0x1) = 8192

I wanted to splice_read 4096 bytes, but it returns 8192 or larger.

It is because the return value of tracing_buffers_splice_read()
does not include "zero out any left over data" bytes.

But tracing_buffers_read() includes these bytes, we make them
consistent.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <49D46674.9030804@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 2 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 94629760dabf..1ce5dc6372b8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3428,7 +3428,19 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
         int size, i;
         size_t ret;
 
-        for (i = 0; i < PIPE_BUFFERS && len; i++, len -= size) {
+        if (*ppos & (PAGE_SIZE - 1)) {
+                WARN_ONCE(1, "Ftrace: previous read must page-align\n");
+                return -EINVAL;
+        }
+
+        if (len & (PAGE_SIZE - 1)) {
+                WARN_ONCE(1, "Ftrace: splice_read should page-align\n");
+                if (len < PAGE_SIZE)
+                        return -EINVAL;
+                len &= PAGE_MASK;
+        }
+
+        for (i = 0; i < PIPE_BUFFERS && len; i++, len -= PAGE_SIZE) {
                 struct page *page;
                 int r;
 
@@ -3467,7 +3479,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
                 spd.partial[i].offset = 0;
                 spd.partial[i].private = (unsigned long)ref;
                 spd.nr_pages++;
-                *ppos += size;
+                *ppos += PAGE_SIZE;
         }
 
         spd.nr_pages = i;