[PATCH] fix crash in entry.S restore_all

Fix the access-above-bottom-of-stack crash.

1. Allows to preserve the valueable optimization

2. Works for NMIs

3.  Doesn't care whether or not there are more of the like instances
   where the stack is left empty.

4. Seems to work for me without the crashes:) 

(akpm: this is still under discussion, although I _think_ it's OK.  You might
want to hold off)

Signed-off-by: Stas Sergeev <stsp@aknet.ru> 
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 1e45ff292bc9..3c73dc865ead 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -245,6 +245,9 @@ syscall_exit:
 
 restore_all:
         movl EFLAGS(%esp), %eax         # mix EFLAGS, SS and CS
+        # Warning: OLDSS(%esp) contains the wrong/random values if we
+        # are returning to the kernel.
+        # See comments in process.c:copy_thread() for details.
         movb OLDSS(%esp), %ah
         movb CS(%esp), %al
         andl $(VM_MASK | (4 << 8) | 3), %eax