xtensa: switch to generic kernel_thread()

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

3 files changed, 59 insertions, 60 deletions

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 18453067c258..d4ec1381aebc 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1833,34 +1833,6 @@ ENTRY(system_call)
 
 
 /*
- * Create a kernel thread
- *
- * int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
- * a2                    a2                 a3             a4
- */
-
-ENTRY(kernel_thread)
-        entry   a1, 16
-
-        mov     a5, a2                  # preserve fn over syscall
-        mov     a7, a3                  # preserve args over syscall
-
-        movi    a3, _CLONE_VM | _CLONE_UNTRACED
-        movi    a2, __NR_clone
-        or      a6, a4, a3              # arg0: flags
-        mov     a3, a1                  # arg1: sp
-        syscall
-
-        beq     a3, a1, 1f              # branch if parent
-        mov     a6, a7                  # args
-        callx4  a5                      # fn(args)
-
-        movi    a2, __NR_exit
-        syscall                         # return value of fn(args) still in a6
-
-1:      retw
-
-/*
  * Do a system call from kernel instead of calling sys_execve, so we end up
  * with proper pt_regs.
  *
@@ -1958,3 +1930,16 @@ ENTRY(ret_from_fork)
 
         j       common_exception_return
 
+/*
+ * Kernel thread creation helper
+ * On entry, set up by copy_thread: a2 = thread_fn, a3 = thread_fn arg
+ *           left from _switch_to: a6 = prev
+ */
+ENTRY(ret_from_kernel_thread)
+
+        call4   schedule_tail
+        mov     a6, a3
+        callx4  a2
+        call4   do_exit
+
+ENDPROC(ret_from_kernel_thread)
diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
index 341c151af919..be52fe437c1b 100644
--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -45,6 +45,7 @@
 #include <asm/regs.h>
 
 extern void ret_from_fork(void);
+extern void ret_from_kernel_thread(void);
 
 struct task_struct *current_set[NR_CPUS] = {&init_task, };
 
@@ -158,18 +159,30 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 /*
  * Copy thread.
  *
+ * There are two modes in which this function is called:
+ * 1) Userspace thread creation,
+ *    regs != NULL, usp_thread_fn is userspace stack pointer.
+ *    It is expected to copy parent regs (in case CLONE_VM is not set
+ *    in the clone_flags) and set up passed usp in the childregs.
+ * 2) Kernel thread creation,
+ *    regs == NULL, usp_thread_fn is the function to run in the new thread
+ *    and thread_fn_arg is its parameter.
+ *    childregs are not used for the kernel threads.
+ *
  * The stack layout for the new thread looks like this:
  *
- *      +------------------------+ <- sp in childregs (= tos)
+ *      +------------------------+
  *      |       childregs        |
  *      +------------------------+ <- thread.sp = sp in dummy-frame
  *      |      dummy-frame       |    (saved in dummy-frame spill-area)
  *      +------------------------+
  *
- * We create a dummy frame to return to ret_from_fork:
- *   a0 points to ret_from_fork (simulating a call4)
+ * We create a dummy frame to return to either ret_from_fork or
+ *   ret_from_kernel_thread:
+ *   a0 points to ret_from_fork/ret_from_kernel_thread (simulating a call4)
  *   sp points to itself (thread.sp)
- *   a2, a3 are unused.
+ *   a2, a3 are unused for userspace threads,
+ *   a2 points to thread_fn, a3 holds thread_fn arg for kernel threads.
  *
  * Note: This is a pristine frame, so we don't need any spill region on top of
  *       childregs.
@@ -185,41 +198,37 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
  * involved.  Much simpler to just not copy those live frames across.
  */
 
-int copy_thread(unsigned long clone_flags, unsigned long usp,
-                unsigned long unused,
-                struct task_struct * p, struct pt_regs * regs)
+int copy_thread(unsigned long clone_flags, unsigned long usp_thread_fn,
+                unsigned long thread_fn_arg,
+                struct task_struct *p, struct pt_regs *unused)
 {
-        struct pt_regs *childregs;
-        unsigned long tos;
-        int user_mode = user_mode(regs);
+        struct pt_regs *childregs = task_pt_regs(p);
 
 #if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
         struct thread_info *ti;
 #endif
 
-        /* Set up new TSS. */
-        tos = (unsigned long)task_stack_page(p) + THREAD_SIZE;
-        if (user_mode)
-                childregs = (struct pt_regs*)(tos - PT_USER_SIZE);
-        else
-                childregs = (struct pt_regs*)tos - 1;
-
-        /* This does not copy all the regs.  In a bout of brilliance or madness,
-           ARs beyond a0-a15 exist past the end of the struct. */
-        *childregs = *regs;
-
         /* Create a call4 dummy-frame: a0 = 0, a1 = childregs. */
         *((int*)childregs - 3) = (unsigned long)childregs;
         *((int*)childregs - 4) = 0;
 
-        childregs->areg[2] = 0;
-        p->set_child_tid = p->clear_child_tid = NULL;
-        p->thread.ra = MAKE_RA_FOR_CALL((unsigned long)ret_from_fork, 0x1);
         p->thread.sp = (unsigned long)childregs;
 
-        if (user_mode(regs)) {
+        if (!(p->flags & PF_KTHREAD)) {
+                struct pt_regs *regs = current_pt_regs();
+                unsigned long usp = usp_thread_fn ?
+                        usp_thread_fn : regs->areg[1];
+
+                p->thread.ra = MAKE_RA_FOR_CALL(
+                                (unsigned long)ret_from_fork, 0x1);
 
+                /* This does not copy all the regs.
+                 * In a bout of brilliance or madness,
+                 * ARs beyond a0-a15 exist past the end of the struct.
+                 */
+                *childregs = *regs;
                 childregs->areg[1] = usp;
+                childregs->areg[2] = 0;
 
                 /* When sharing memory with the parent thread, the child
                    usually starts on a pristine stack, so we have to reset
@@ -254,11 +263,19 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 // FIXME: we need to set THREADPTR in thread_info...
                 if (clone_flags & CLONE_SETTLS)
                         childregs->areg[2] = childregs->areg[6];
-
         } else {
-                /* In kernel space, we start a new thread with a new stack. */
-                childregs->wmask = 1;
-                childregs->areg[1] = tos;
+                p->thread.ra = MAKE_RA_FOR_CALL(
+                                (unsigned long)ret_from_kernel_thread, 1);
+
+                /* pass parameters to ret_from_kernel_thread:
+                 * a2 = thread_fn, a3 = thread_fn arg
+                 */
+                *((int *)childregs - 1) = thread_fn_arg;
+                *((int *)childregs - 2) = usp_thread_fn;
+
+                /* Childregs are only used when we're going to userspace
+                 * in which case start_thread will set them up.
+                 */
         }
 
 #if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
@@ -354,8 +371,6 @@ long xtensa_clone(unsigned long clone_flags, unsigned long newsp,
                   void __user *child_tid, long a5,
                   struct pt_regs *regs)
 {
-        if (!newsp)
-                newsp = regs->areg[1];
         return do_fork(clone_flags, newsp, regs, 0, parent_tid, child_tid);
 }
 
diff --git a/arch/xtensa/kernel/xtensa_ksyms.c b/arch/xtensa/kernel/xtensa_ksyms.c
index a8b9f1fd1e17..afe058b24e6e 100644
--- a/arch/xtensa/kernel/xtensa_ksyms.c
+++ b/arch/xtensa/kernel/xtensa_ksyms.c
@@ -43,7 +43,6 @@ EXPORT_SYMBOL(__strncpy_user);
 EXPORT_SYMBOL(clear_page);
 EXPORT_SYMBOL(copy_page);
 
-EXPORT_SYMBOL(kernel_thread);
 EXPORT_SYMBOL(empty_zero_page);
 
 /*