x86: split ret_from_fork

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

7 files changed, 67 insertions, 85 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8ec3a1aa4abd..d93eb9d1bb97 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -97,6 +97,7 @@ config X86
         select KTIME_SCALAR if X86_32
         select GENERIC_STRNCPY_FROM_USER
         select GENERIC_STRNLEN_USER
+        select GENERIC_KERNEL_THREAD
 
 config INSTRUCTION_DECODER
         def_bool (KPROBES || PERF_EVENTS || UPROBES)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d048cad9bcad..078f3fdedf95 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -589,11 +589,6 @@ typedef struct {
 } mm_segment_t;
 
 
-/*
- * create a kernel thread without removing it from tasklists
- */
-extern int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
-
 /* Free all resources held by a thread. */
 extern void release_thread(struct task_struct *);
 
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 623f28837476..ac1107346fc9 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -994,15 +994,20 @@ END(spurious_interrupt_bug)
  */
         .popsection
 
-ENTRY(kernel_thread_helper)
-        pushl $0                # fake return address for unwinder
+ENTRY(ret_from_kernel_thread)
         CFI_STARTPROC
-        movl %edi,%eax
-        call *%esi
+        pushl_cfi %eax
+        call schedule_tail
+        GET_THREAD_INFO(%ebp)
+        popl_cfi %eax
+        pushl_cfi $0x0202               # Reset kernel eflags
+        popfl_cfi
+        movl PT_EBP(%esp),%eax
+        call *PT_EBX(%esp)
         call do_exit
         ud2                     # padding for call trace
         CFI_ENDPROC
-ENDPROC(kernel_thread_helper)
+ENDPROC(ret_from_kernel_thread)
 
 #ifdef CONFIG_XEN
 /* Xen doesn't set %esp to be precisely what the normal sysenter
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 69babd8c834f..5526d17db676 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -450,7 +450,7 @@ ENTRY(ret_from_fork)
         RESTORE_REST
 
         testl $3, CS-ARGOFFSET(%rsp)            # from kernel_thread?
-        jz   retint_restore_args
+        jz   1f
 
         testl $_TIF_IA32, TI_flags(%rcx)        # 32-bit compat task needs IRET
         jnz  int_ret_from_sys_call
@@ -458,6 +458,16 @@ ENTRY(ret_from_fork)
         RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET
         jmp ret_from_sys_call                   # go to the SYSRET fastpath
 
+1:
+        subq $REST_SKIP, %rsp   # move the stack pointer back
+        CFI_ADJUST_CFA_OFFSET   REST_SKIP
+        movq %rbp, %rdi
+        call *%rbx
+        # exit
+        mov %eax, %edi
+        call do_exit
+        ud2                     # padding for call trace
+
         CFI_ENDPROC
 END(ret_from_fork)
 
@@ -1206,21 +1216,6 @@ bad_gs:
         jmp  2b
         .previous
 
-ENTRY(kernel_thread_helper)
-        pushq $0                # fake return address
-        CFI_STARTPROC
-        /*
-         * Here we are in the child and the registers are set as they were
-         * at kernel_thread() invocation in the parent.
-         */
-        call *%rsi
-        # exit
-        mov %eax, %edi
-        call do_exit
-        ud2                     # padding for call trace
-        CFI_ENDPROC
-END(kernel_thread_helper)
-
 /*
  * execve(). This function needs to use IRET, not SYSRET, to set up all state properly.
  *
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7162e9c1f598..6947ec968bf8 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -299,44 +299,6 @@ sys_clone(unsigned long clone_flags, unsigned long newsp,
 }
 
 /*
- * This gets run with %si containing the
- * function to call, and %di containing
- * the "args".
- */
-extern void kernel_thread_helper(void);
-
-/*
- * Create a kernel thread
- */
-int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
-{
-        struct pt_regs regs;
-
-        memset(&regs, 0, sizeof(regs));
-
-        regs.si = (unsigned long) fn;
-        regs.di = (unsigned long) arg;
-
-#ifdef CONFIG_X86_32
-        regs.ds = __USER_DS;
-        regs.es = __USER_DS;
-        regs.fs = __KERNEL_PERCPU;
-        regs.gs = __KERNEL_STACK_CANARY;
-#else
-        regs.ss = __KERNEL_DS;
-#endif
-
-        regs.orig_ax = -1;
-        regs.ip = (unsigned long) kernel_thread_helper;
-        regs.cs = __KERNEL_CS | get_kernel_rpl();
-        regs.flags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
-
-        /* Ok, create the new process.. */
-        return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
-}
-EXPORT_SYMBOL(kernel_thread);
-
-/*
  * sys_execve() executes a new program.
  */
 long sys_execve(const char __user *name,
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 75fcad146def..c9939875d267 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -57,6 +57,7 @@
 #include <asm/switch_to.h>
 
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
+asmlinkage void ret_from_kernel_thread(void) __asm__("ret_from_kernel_thread");
 
 /*
  * Return saved PC of a blocked thread.
@@ -127,23 +128,39 @@ void release_thread(struct task_struct *dead_task)
 }
 
 int copy_thread(unsigned long clone_flags, unsigned long sp,
-        unsigned long unused,
+        unsigned long arg,
         struct task_struct *p, struct pt_regs *regs)
 {
-        struct pt_regs *childregs;
+        struct pt_regs *childregs = task_pt_regs(p);
         struct task_struct *tsk;
         int err;
 
-        childregs = task_pt_regs(p);
+        p->thread.sp = (unsigned long) childregs;
+        p->thread.sp0 = (unsigned long) (childregs+1);
+
+        if (unlikely(!regs)) {
+                /* kernel thread */
+                memset(childregs, 0, sizeof(struct pt_regs));
+                p->thread.ip = (unsigned long) ret_from_kernel_thread;
+                task_user_gs(p) = __KERNEL_STACK_CANARY;
+                childregs->ds = __USER_DS;
+                childregs->es = __USER_DS;
+                childregs->fs = __KERNEL_PERCPU;
+                childregs->bx = sp;     /* function */
+                childregs->bp = arg;
+                childregs->orig_ax = -1;
+                childregs->cs = __KERNEL_CS | get_kernel_rpl();
+                childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
+                p->fpu_counter = 0;
+                p->thread.io_bitmap_ptr = NULL;
+                memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
+                return 0;
+        }
         *childregs = *regs;
         childregs->ax = 0;
         childregs->sp = sp;
 
-        p->thread.sp = (unsigned long) childregs;
-        p->thread.sp0 = (unsigned long) (childregs+1);
-
         p->thread.ip = (unsigned long) ret_from_fork;
-
         task_user_gs(p) = get_user_gs(regs);
 
         p->fpu_counter = 0;
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 0a980c9d7cb8..937f2af6f2d4 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -146,29 +146,18 @@ static inline u32 read_32bit_tls(struct task_struct *t, int tls)
 }
 
 int copy_thread(unsigned long clone_flags, unsigned long sp,
-                unsigned long unused,
+                unsigned long arg,
         struct task_struct *p, struct pt_regs *regs)
 {
         int err;
         struct pt_regs *childregs;
         struct task_struct *me = current;
 
-        childregs = ((struct pt_regs *)
-                        (THREAD_SIZE + task_stack_page(p))) - 1;
-        *childregs = *regs;
-
-        childregs->ax = 0;
-        if (user_mode(regs))
-                childregs->sp = sp;
-        else
-                childregs->sp = (unsigned long)childregs;
-
+        p->thread.sp0 = (unsigned long)task_stack_page(p) + THREAD_SIZE;
+        childregs = task_pt_regs(p);
         p->thread.sp = (unsigned long) childregs;
-        p->thread.sp0 = (unsigned long) (childregs+1);
         p->thread.usersp = me->thread.usersp;
-
         set_tsk_thread_flag(p, TIF_FORK);
-
         p->fpu_counter = 0;
         p->thread.io_bitmap_ptr = NULL;
 
@@ -178,6 +167,24 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
         p->thread.fs = p->thread.fsindex ? 0 : me->thread.fs;
         savesegment(es, p->thread.es);
         savesegment(ds, p->thread.ds);
+        memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
+
+        if (unlikely(!regs)) {
+                /* kernel thread */
+                memset(childregs, 0, sizeof(struct pt_regs));
+                childregs->sp = (unsigned long)childregs;
+                childregs->ss = __KERNEL_DS;
+                childregs->bx = sp; /* function */
+                childregs->bp = arg;
+                childregs->orig_ax = -1;
+                childregs->cs = __KERNEL_CS | get_kernel_rpl();
+                childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
+                return 0;
+        }
+        *childregs = *regs;
+
+        childregs->ax = 0;
+        childregs->sp = sp;
 
         err = -ENOMEM;
         memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));