sched/x86: Rewrite the switch_to() code
Move the low-level context switch code to an out-of-line asm stub instead of
using complex inline asm. This allows constructing a new stack frame for the
child process to make it seamlessly flow to ret_from_fork without an extra
test and branch in __switch_to(). It also improves code generation for
__schedule() by using the C calling convention instead of clobbering all
registers.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1471106302-10159-5-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d86be29..4bedbc0 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -133,17 +133,20 @@
unsigned long arg, struct task_struct *p, unsigned long tls)
{
struct pt_regs *childregs = task_pt_regs(p);
+ struct fork_frame *fork_frame = container_of(childregs, struct fork_frame, regs);
+ struct inactive_task_frame *frame = &fork_frame->frame;
struct task_struct *tsk;
int err;
- p->thread.sp = (unsigned long) childregs;
+ frame->bp = 0;
+ p->thread.sp = (unsigned long) fork_frame;
p->thread.sp0 = (unsigned long) (childregs+1);
memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
if (unlikely(p->flags & PF_KTHREAD)) {
/* kernel thread */
memset(childregs, 0, sizeof(struct pt_regs));
- p->thread.ip = (unsigned long) ret_from_kernel_thread;
+ frame->ret_addr = (unsigned long) ret_from_kernel_thread;
task_user_gs(p) = __KERNEL_STACK_CANARY;
childregs->ds = __USER_DS;
childregs->es = __USER_DS;
@@ -161,7 +164,7 @@
if (sp)
childregs->sp = sp;
- p->thread.ip = (unsigned long) ret_from_fork;
+ frame->ret_addr = (unsigned long) ret_from_fork;
task_user_gs(p) = get_user_gs(current_pt_regs());
p->thread.io_bitmap_ptr = NULL;
