x86/mm/pat: Do a small optimization and fix in reserve_memtype

From: Pan Xinhui <[email protected]>

It's safe and more reasonable to unlock memtype_lock right after rbt_memtype_check_insert. It's not cool to call kfree, pr_info, etc with this lock held. So move spin_unlock a little ahead.

memory_lock protects data stored in rb-tree, if *new* succeed to be stored into the rb-tree, we might hit panic. Because we access *new* in dprintk "cattr_name(new->type)". data stored in the rb-tree might be freed at any possbile time. It's abviously wrong to access such data without lock. So save new->type to actual_type, and use actual_type in dprintk.

---
change from V1:
fix an access of *new* without memtype_lock held.

---
 arch/x86/mm/pat.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

index 188e3e0..f3c49fa 100644
@@ -538,22 +538,20 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
 	new->type	= actual_type;
 
 	spin_lock(&memtype_lock);
-
 	err = rbt_memtype_check_insert(new, new_type);
+	actual_type = new->type;
+	spin_unlock(&memtype_lock);
+
 	if (err) {
 		pr_info("x86/PAT: reserve_memtype failed [mem %#010Lx-%#010Lx], track %s, req %s\n",
 			start, end - 1,
 			cattr_name(new->type), cattr_name(req_type));
 		kfree(new);
-		spin_unlock(&memtype_lock);
-
 		return err;
 	}
 
-	spin_unlock(&memtype_lock);
-
 	dprintk("reserve_memtype added [mem %#010Lx-%#010Lx], track %s, req %s, ret %s\n",
-		start, end - 1, cattr_name(new->type), cattr_name(req_type),
+		start, end - 1, cattr_name(actual_type), cattr_name(req_type),
 		new_type ? cattr_name(*new_type) : "-");
 
 	return err;

1.9.1

hi, tglx
thanks for your reply :)

191 int rbt_memtype_check_insert(struct memtype *new,
192 enum page_cache_mode *ret_type)
193 {
194 int err = 0;
195
196 err = memtype_rb_check_conflict(&memtype_rbroot, new->start, new->end,
197 new->type, ret_type);
198
199 if (!err) {
200 if (ret_type)
201 new->type = *ret_type;
202
So new->type might be set to *ret_type.

136 if (match->type != found_type && newtype == NULL)
137 goto failure;
138
139 dprintk("Overlap at 0x%Lx-0x%Lx\n", match->start, match->end);
140 found_type = match->type;
141
142 node = rb_next(&match->rb);
143 while (node) {
144 match = container_of(node, struct memtype, rb);
145
146 if (match->start >= end) /* Checked all possible matches */
147 goto success;
148
149 if (is_node_overlap(match, start, end) &&
150 match->type != found_type) {
151 goto failure;
152 }
153
154 node = rb_next(&match->rb);
155 }
156 success:
157 if (newtype)
158 *newtype = found_type;

So *ret_type might be set to found_type(match->type),

The call train is deep, it took me long time to review them.
As actual_type != new->type is possible, we need save new->type to actual_type.

thanks
xinhui

Fair enough. But that wants to have a comment in the code as any casual reader will trip over this.

Thanks,

tglx