[RFC v8 05/20] um: extend arch_switch_to for alternate SUBARCH

[Hajime Tazaki]

This commit introduces additional argument of previous task when
context switch happens.  New SUBARCH can use the new information to
switch tasks in a subarch-specific manner.

The patch is particularly required by library mode, implemented as a
SUBARCH of UML.  Having access to the previous thread will be required
in the library mode for it to implement thread switching correctly.

Signed-off-by: Hajime Tazaki <thehajime at gmail.com>
---
 arch/um/kernel/process.c  | 6 +++---
 arch/x86/um/ptrace_32.c   | 2 +-
 arch/x86/um/syscalls_64.c | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 2a986ece5478..9b0a36f64339 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -83,7 +83,7 @@ static inline void set_current(struct task_struct *task)
 		{ external_pid(), task });
 }
 
-extern void arch_switch_to(struct task_struct *to);
+extern void arch_switch_to(struct task_struct *from, struct task_struct *to);
 
 void *__switch_to(struct task_struct *from, struct task_struct *to)
 {
@@ -91,7 +91,7 @@ void *__switch_to(struct task_struct *from, struct task_struct *to)
 	set_current(to);
 
 	switch_threads(&from->thread.switch_buf, &to->thread.switch_buf);
-	arch_switch_to(current);
+	arch_switch_to(from, to);
 
 	return current->thread.prev_sched;
 }
@@ -149,7 +149,7 @@ void fork_handler(void)
 	 * arch_switch_to isn't needed. We could want to apply this to
 	 * improve performance. -bb
 	 */
-	arch_switch_to(current);
+	arch_switch_to(NULL, current);
 
 	current->thread.prev_sched = NULL;
 
diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
index 2497bac56066..0f184710d4ca 100644
--- a/arch/x86/um/ptrace_32.c
+++ b/arch/x86/um/ptrace_32.c
@@ -11,7 +11,7 @@
 
 extern int arch_switch_tls(struct task_struct *to);
 
-void arch_switch_to(struct task_struct *to)
+void arch_switch_to(struct task_struct *from, struct task_struct *to)
 {
 	int err = arch_switch_tls(to);
 	if (!err)
diff --git a/arch/x86/um/syscalls_64.c b/arch/x86/um/syscalls_64.c
index 58f51667e2e4..2ef9474d2bd2 100644
--- a/arch/x86/um/syscalls_64.c
+++ b/arch/x86/um/syscalls_64.c
@@ -80,7 +80,7 @@ SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
 	return arch_prctl(current, option, (unsigned long __user *) arg2);
 }
 
-void arch_switch_to(struct task_struct *to)
+void arch_switch_to(struct task_struct *from, struct task_struct *to)
 {
 	if ((to->thread.arch.fs == 0) || (to->mm == NULL))
 		return;
-- 
2.21.0 (Apple Git-122.2)