Re: [PATCH RFC 7/8] s390/jump-label: add arch_jump_label_transform_early()

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 09/30/2011 07:48 AM, Jan Glauber wrote:
> On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote:
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>> This allows jump-label entries to be modified early, in a pre-SMP
>> environment.
>>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>> Cc: Jan Glauber <jang@linux.vnet.ibm.com>
> Hi Jeremy,
>
> Your patch looks fine, if you can fix the minor compiler warnings
> below. Excluding stop_machine() on pre-SMP also looks safer too me.

Do you think there would be an actual problem, or are you just being
cautious?

It seems to me - in general - stop_machine could just be defined to be a
no-op (ie, just directly calls the callback) until enough SMP is
initialized for it to make sense, rather than having to make every user
work around it (if there's a chance they might call it early).

>   CC      arch/s390/kernel/jump_label.o
> arch/s390/kernel/jump_label.c: In function ‘__jump_label_transform’:
> arch/s390/kernel/jump_label.c:41:2: error: ‘rc’ undeclared (first use in this function)
> arch/s390/kernel/jump_label.c:41:2: note: each undeclared identifier is reported only once for each function it appears in
> arch/s390/kernel/jump_label.c:41:2: warning: passing argument 1 of ‘probe_kernel_write’ makes pointer from integer without a cast [enabled by default]
> include/linux/uaccess.h:108:21: note: expected ‘void *’ but argument is of type ‘jump_label_t’
> arch/s390/kernel/jump_label.c:28:19: warning: unused variable ‘args’ [-Wunused-variable]
> make[2]: *** [arch/s390/kernel/jump_label.o] Error 1
>
>

Like so?

>From 9572689d1e5e6f54a1936a1dca09a6920d1bce27 Mon Sep 17 00:00:00 2001
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Thu, 29 Sep 2011 10:58:46 -0700
Subject: [PATCH] s390/jump-label: add arch_jump_label_transform_early()

This allows jump-label entries to be modified early, in a pre-SMP
environment.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Jan Glauber <jang@linux.vnet.ibm.com>

diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
index 44cc06b..4fbe63b 100644
--- a/arch/s390/kernel/jump_label.c
+++ b/arch/s390/kernel/jump_label.c
@@ -18,26 +18,15 @@ struct insn {
 } __packed;
 
 struct insn_args {
-	unsigned long *target;
-	struct insn *insn;
-	ssize_t size;
+	struct jump_entry *entry;
+	enum jump_label_type type;
 };
 
-static int __arch_jump_label_transform(void *data)
+static void __jump_label_transform(struct jump_entry *entry,
+				   enum jump_label_type type)
 {
-	struct insn_args *args = data;
-	int rc;
-
-	rc = probe_kernel_write(args->target, args->insn, args->size);
-	WARN_ON_ONCE(rc < 0);
-	return 0;
-}
-
-void arch_jump_label_transform(struct jump_entry *entry,
-			       enum jump_label_type type)
-{
-	struct insn_args args;
 	struct insn insn;
+	int rc;
 
 	if (type == JUMP_LABEL_ENABLE) {
 		/* brcl 15,offset */
@@ -49,11 +38,33 @@ void arch_jump_label_transform(struct jump_entry *entry,
 		insn.offset = 0;
 	}
 
-	args.target = (void *) entry->code;
-	args.insn = &insn;
-	args.size = JUMP_LABEL_NOP_SIZE;
+	rc = probe_kernel_write((void *)entry->code, &insn, JUMP_LABEL_NOP_SIZE);
+	WARN_ON_ONCE(rc < 0);
+}
 
-	stop_machine(__arch_jump_label_transform, &args, NULL);
+static int __sm_arch_jump_label_transform(void *data)
+{
+	struct insn_args *args = data;
+
+	__jump_label_transform(args->entry, args->type);
+	return 0;
+}
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	struct insn_args args;
+
+	args.entry = entry;
+	args.type = type;
+
+	stop_machine(__sm_arch_jump_label_transform, &args, NULL);
+}
+
+void __init arch_jump_label_transform_early(struct jump_entry *entry,
+					    enum jump_label_type type)
+{
+	__jump_label_transform(entry, type);
 }
 
 #endif

	J