um: Move uml_postsetup in the init_thread stack

atomic_notifier_chain_register() and uml_postsetup() do call kernel code
that rely on the "current" kernel macro and a valid task_struct resp.
thread_info struct. Give those functions a valid stack by moving
uml_postsetup() in the init_thread stack. This moves enables a panic()
call in this early code to generate a valid stacktrace, instead of
crashing.
E.g. when an UML kernel is started with an initrd but too few physical
memory the panic() call get's actually processed.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

3 files changed, 12 insertions, 6 deletions

diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index 41c8c774ec10..ca1843e1df15 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -56,6 +56,7 @@ extern unsigned long brk_start;
 extern unsigned long host_task_size;
 
 extern int linux_main(int argc, char **argv);
+extern void uml_finishsetup(void);
 
 struct siginfo;
 extern void (*sig_info[])(int, struct siginfo *si, struct uml_pt_regs *);
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 926ecdceba86..07f798f4bcee 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -226,6 +226,16 @@ static struct notifier_block panic_exit_notifier = {
         .priority               = 0
 };
 
+void uml_finishsetup(void)
+{
+        atomic_notifier_chain_register(&panic_notifier_list,
+                                       &panic_exit_notifier);
+
+        uml_postsetup();
+
+        new_thread_handler();
+}
+
 /* Set during early boot */
 unsigned long task_size;
 EXPORT_SYMBOL(task_size);
@@ -326,11 +336,6 @@ int __init linux_main(int argc, char **argv)
                 printf("Kernel virtual memory size shrunk to %lu bytes\n",
                        virtmem_size);
 
-        atomic_notifier_chain_register(&panic_notifier_list,
-                                       &panic_exit_notifier);
-
-        uml_postsetup();
-
         stack_protections((unsigned long) &init_thread_info);
         os_flush_stdout();
 
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 50ebeae5cbb3..7a9777570a62 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -586,7 +586,7 @@ int start_idle_thread(void *stack, jmp_buf *switch_buf)
         n = setjmp(initial_jmpbuf);
         switch (n) {
         case INIT_JMP_NEW_THREAD:
-                (*switch_buf)[0].JB_IP = (unsigned long) new_thread_handler;
+                (*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
                 (*switch_buf)[0].JB_SP = (unsigned long) stack +
                         UM_THREAD_SIZE - sizeof(void *);
                 break;