linux-kernel - [PATCH 3/3] z3fold: protect handle reads

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Message-Id: <20191127152345.8059852f60947686674d726d@gmail.com>
Date:   Wed, 27 Nov 2019 15:23:45 +0100
From:   Vitaly Wool <vitalywool@...il.com>
To:     <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 3/3] z3fold: protect handle reads

We need to make sure slots are protected on reading a handle. Since
handles are modified by free_handle() which only takes slot rwlock,
that lock should be used when handles are read.

Signed-off-by: Vitaly Wool <vitaly.vul@...y.com>
---
 mm/z3fold.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index f2a75418e248..43754d8ebce8 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -486,8 +486,12 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 /* only for LAST bud, returns zero otherwise */
 static unsigned short handle_to_chunks(unsigned long handle)
 {
-	unsigned long addr = *(unsigned long *)handle;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
+	unsigned long addr;
 
+	read_lock(&slots->lock);
+	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 }
 
@@ -499,10 +503,13 @@ static unsigned short handle_to_chunks(unsigned long handle)
 static enum buddy handle_to_buddy(unsigned long handle)
 {
 	struct z3fold_header *zhdr;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 	unsigned long addr;
 
+	read_lock(&slots->lock);
 	WARN_ON(handle & (1 << PAGE_HEADLESS));
 	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 	return (addr - zhdr->first_num) & BUDDY_MASK;
 }
-- 
2.17.1