linux-kernel - [PATCH V5] x86/mm/pat: Do a small optimization and fix in reserve

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Date:	Thu, 23 Jul 2015 09:52:57 +0800
From:	Pan Xinhui <xinhuix.pan@...el.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, bp@...e.de, toshi.kani@...com,
	jgross@...e.com, mcgrof@...e.com,
	"mnipxh@....com" <mnipxh@....com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>
Subject: [PATCH V5] x86/mm/pat: Do a small optimization and fix in reserve_memtype

From: Pan Xinhui <xinhuix.pan@...el.com>

It's more reasonable to unlock memtype_lock right after
rbt_memtype_check_insert. All pat_rbtree operations need to be performed
while holding the memtype_lock. But codes like kfree, pr_info, etc have
nothing to do with this lock. So move spin_unlock a little ahead.

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 held.

We use actual_type instead of new->type in dprintk. Two benefits, 1) We
don't touch *new* here now so panic can be avoided. 2) As new->type is
same with *new_type, We needn't to print it again, what's more, this
actual_type's output can help dubug. When new_type is NULL, actual_type
is equal to new->type, So no key information is lost.

Do a minor codes style improvement.

Signed-off-by: Pan Xinhui <xinhuix.pan@...el.com>
---
change from v4:
	codes style improvement by removing {}.
	@sorry for that, make reviewing a patch so much complex, this should be done in V4.
change from v3:
	output actual_type instead of new->type.
	codes style improvement.
	update comments.
change from v2:
	update comments.
change from V1:
	fix an access of *new* without memtype_lock held.
---
 arch/x86/mm/pat.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 188e3e0..268b2c8 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -520,14 +520,10 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
 		*new_type = actual_type;
 
 	is_range_ram = pat_pagerange_is_ram(start, end);
-	if (is_range_ram == 1) {
-
-		err = reserve_ram_pages_type(start, end, req_type, new_type);
-
-		return err;
-	} else if (is_range_ram < 0) {
+	if (is_range_ram == 1)
+		return reserve_ram_pages_type(start, end, req_type, new_type);
+	else if (is_range_ram < 0)
 		return -EINVAL;
-	}
 
 	new  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
 	if (!new)
@@ -538,22 +534,19 @@ 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);
+	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
--
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