[ARM] 3911/2: Simplify alloc_thread_info on ARM

Remove ARM local cache of 4 struct thread_info.
Can cause oops under certain circumstances.

Russell indicated the original optimization was
required on older kernels to avoid thread starvation
on memory fragmentation, but may no longer be
required.  I've updated the patch to 19rc4 and
ensured no <config.h> dain-bramage slipped in this
time (sorry about that).

Original description follows:

I was given some test results which pointed to an
Oops in alloc_thread_info (happened 2x), and after
looking at the code, I see that ARM has its own
local cache of 4 struct thread_info. There wasn't
any clear (to me) synchronization between the
alloc_thread_info and the free_thread_info.

I looked over the other arch, and they all simply
allocate them on an as needed basis, so I simplified
the ARM to do the same, based on the other arch
(e.g. PPC) and the folks doing the testing have
indicated that this fixed the oops.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/process.c

@@ -280,67 +280,6 @@ void show_fpregs(struct user_fp *regs)
 		(unsigned long)regs->fpcr);
 }
 
-/*
- * Task structure and kernel stack allocation.
- */
-struct thread_info_list {
-	unsigned long *head;
-	unsigned int nr;
-};
-
-static DEFINE_PER_CPU(struct thread_info_list, thread_info_list) = { NULL, 0 };
-
-#define EXTRA_TASK_STRUCT	4
-
-struct thread_info *alloc_thread_info(struct task_struct *task)
-{
-	struct thread_info *thread = NULL;
-
-	if (EXTRA_TASK_STRUCT) {
-		struct thread_info_list *th = &get_cpu_var(thread_info_list);
-		unsigned long *p = th->head;
-
-		if (p) {
-			th->head = (unsigned long *)p[0];
-			th->nr -= 1;
-		}
-		put_cpu_var(thread_info_list);
-
-		thread = (struct thread_info *)p;
-	}
-
-	if (!thread)
-		thread = (struct thread_info *)
-			   __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER);
-
-#ifdef CONFIG_DEBUG_STACK_USAGE
-	/*
-	 * The stack must be cleared if you want SYSRQ-T to
-	 * give sensible stack usage information
-	 */
-	if (thread)
-		memzero(thread, THREAD_SIZE);
-#endif
-	return thread;
-}
-
-void free_thread_info(struct thread_info *thread)
-{
-	if (EXTRA_TASK_STRUCT) {
-		struct thread_info_list *th = &get_cpu_var(thread_info_list);
-		if (th->nr < EXTRA_TASK_STRUCT) {
-			unsigned long *p = (unsigned long *)thread;
-			p[0] = (unsigned long)th->head;
-			th->head = p;
-			th->nr += 1;
-			put_cpu_var(thread_info_list);
-			return;
-		}
-		put_cpu_var(thread_info_list);
-	}
-	free_pages((unsigned long)thread, THREAD_SIZE_ORDER);
-}
-
 /*
  * Free current thread data structures etc..
  */

include/asm-arm/thread_info.h

@@ -94,8 +94,18 @@ static inline struct thread_info *current_thread_info(void)
 	return (struct thread_info *)(sp & ~(THREAD_SIZE - 1));
 }
 
-extern struct thread_info *alloc_thread_info(struct task_struct *task);
-extern void free_thread_info(struct thread_info *);
+/* thread information allocation */
+#ifdef CONFIG_DEBUG_STACK_USAGE
+#define alloc_thread_info(tsk) \
+	((struct thread_info *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, \
+		THREAD_SIZE_ORDER))
+#else
+#define alloc_thread_info(tsk) \
+	((struct thread_info *)__get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER))
+#endif
+
+#define free_thread_info(info) \
+	free_pages((unsigned long)info, THREAD_SIZE_ORDER);
 
 #define thread_saved_pc(tsk)	\
 	((unsigned long)(pc_pointer(task_thread_info(tsk)->cpu_context.pc)))