commit a343c75d338aa2afaea4a2a8e40de9e67b6fb4a7
author H. Peter Anvin <hpa@zytor.com> Mon Oct 12 14:11:09 2009 -0700
committer H. Peter Anvin <hpa@zytor.com> Mon Oct 12 14:19:34 2009 -0700
tree 1c6f6f764e01048a9d6b6155ce2cc23c92cad4be
parent def3c5d0a34e4b09b3cea4435c17209ad347104d

x86: use kernel_stack_pointer() in dumpstack.c

The way to obtain a kernel-mode stack pointer from a struct pt_regs in
32-bit mode is "subtle": the stack doesn't actually contain the stack
pointer, but rather the location where it would have been marks the
actual previous stack frame.  For clarity, use kernel_stack_pointer()
instead of coding this weirdness explicitly.

Furthermore, user_mode() is only valid when the process is known to
not run in V86 mode.  Use the safer user_mode_vm() instead.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/dumpstack.c

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 2d8a371..b8ce165 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -268,11 +268,12 @@
 
 	show_registers(regs);
 #ifdef CONFIG_X86_32
-	sp = (unsigned long) (&regs->sp);
-	savesegment(ss, ss);
-	if (user_mode(regs)) {
+	if (user_mode_vm(regs)) {
 		sp = regs->sp;
 		ss = regs->ss & 0xffff;
+	} else {
+		sp = kernel_stack_pointer(regs);
+		savesegment(ss, ss);
 	}
 	printk(KERN_EMERG "EIP: [<%08lx>] ", regs->ip);
 	print_symbol("%s", regs->ip);