x86/asm/entry: Delay loading sp0 slightly on task switch

The change:

  75182b1632a8 ("x86/asm/entry: Switch all C consumers of kernel_stack to this_cpu_sp0()")

had the unintended side effect of changing the return value of
current_thread_info() during part of the context switch process.
Change it back.

This has no effect as far as I can tell -- it's just for
consistency.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/9fcaa47dd8487db59eed7a3911b6ae409476763e.1425692936.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d3460af3d27a..0405cab6634d 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -256,11 +256,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         fpu = switch_fpu_prepare(prev_p, next_p, cpu);
 
         /*
-         * Reload esp0.
-         */
-        load_sp0(tss, next);
-
-        /*
          * Save away %gs. No need to save %fs, as it was saved on the
          * stack on entry.  No need to save %es and %ds, as those are
          * always kernel segments while inside the kernel.  Doing this
@@ -310,6 +305,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
          */
         arch_end_context_switch(next_p);
 
+        /*
+         * Reload esp0.  This changes current_thread_info().
+         */
+        load_sp0(tss, next);
+
         this_cpu_write(kernel_stack,
                   (unsigned long)task_stack_page(next_p) +
                   THREAD_SIZE - KERNEL_STACK_OFFSET);