[PATCH] x86: fix oprofile kernel callgraph regression

Fix x86 oprofile regression introduced by:
  commit c34d1b4d165c67b966bca4aba026443d7ff161eb
  [PATCH] mm: kill check_user_page_readable

That commit reorganized tests for the userspace stack walking moving all
those tests into dump_backtrace(), however, dump_backtrace() was used for
both userspace and kernel stalk walking.  The result is typically no
recorded callgraph information for kernel samples.

Revive the original function as dump_kernel_backtrace() and rename the
other to dump_user_backtrace() to avoid future confusion.

Signed-off-by: Gerald Britton <gbritton@alum.mit.edu>
Apology-from: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/i386/oprofile/backtrace.c b/arch/i386/oprofile/backtrace.c
index acc1813..c049ce4 100644 (file)
--- a/arch/i386/oprofile/backtrace.c
+++ b/arch/i386/oprofile/backtrace.c
@@ -20,7 +20,20 @@ struct frame_head {
 } __attribute__((packed));
 
 static struct frame_head *
-dump_backtrace(struct frame_head * head)
+dump_kernel_backtrace(struct frame_head * head)
+{
+       oprofile_add_trace(head->ret);
+
+       /* frame pointers should strictly progress back up the stack
+        * (towards higher addresses) */
+       if (head >= head->ebp)
+               return NULL;
+
+       return head->ebp;
+}
+
+static struct frame_head *
+dump_user_backtrace(struct frame_head * head)
 {
        struct frame_head bufhead[2];
 
@@ -105,10 +118,10 @@ x86_backtrace(struct pt_regs * const regs, unsigned int depth)
 
        if (!user_mode_vm(regs)) {
                while (depth-- && valid_kernel_stack(head, regs))
-                       head = dump_backtrace(head);
+                       head = dump_kernel_backtrace(head);
                return;
        }
 
        while (depth-- && head)
-               head = dump_backtrace(head);
+               head = dump_user_backtrace(head);
 }