Patchwork [3.8.y.z,extended,stable] Patch "zram: use zram->lock to protect zram_free_page() in swap free" has been added to staging queue

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Submitter Luis Henriques
Date July 9, 2013, 4:28 p.m.
Message ID <1373387282-20920-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/257751/
State New
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Luis Henriques - July 9, 2013, 4:28 p.m.
This is a note to let you know that I have just added a patch titled

    zram: use zram->lock to protect zram_free_page() in swap free

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From f56c0e44628257f97063089eb865d5eb2dfdd642 Mon Sep 17 00:00:00 2001
From: Jiang Liu <liuj97@gmail.com>
Date: Fri, 7 Jun 2013 00:07:23 +0800
Subject: [PATCH] zram: use zram->lock to protect zram_free_page() in swap free
 notify path

commit 57ab048532c0d975538cebd4456491b5c34248f4 upstream.

zram_slot_free_notify() is free-running without any protection from
concurrent operations. So there are race conditions between
zram_bvec_read()/zram_bvec_write() and zram_slot_free_notify(),
and possible consequences include:
1) Trigger BUG_ON(!handle) on zram_bvec_write() side.
2) Access to freed pages on zram_bvec_read() side.
3) Break some fields (bad_compress, good_compress, pages_stored)
   in zram->stats if the swap layer makes concurrently call to
   zram_slot_free_notify().

So enhance zram_slot_free_notify() to acquire writer lock on zram->lock
before calling zram_free_page().

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ luis: backported to 3.8: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/staging/zram/zram_drv.c | 2 ++
 drivers/staging/zram/zram_drv.h | 5 +++--
 2 files changed, 5 insertions(+), 2 deletions(-)

--
1.8.1.2

Patch

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index c9c1e0e..0113897 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -615,7 +615,9 @@  static void zram_slot_free_notify(struct block_device *bdev,
 	struct zram *zram;

 	zram = bdev->bd_disk->private_data;
+	down_write(&zram->lock);
 	zram_free_page(zram, index);
+	up_write(&zram->lock);
 	zram_stat64_inc(zram, &zram->stats.notify_free);
 }

diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..4265ab4 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -92,8 +92,9 @@  struct zram {
 	void *compress_buffer;
 	struct table *table;
 	spinlock_t stat64_lock;	/* protect 64-bit stats */
-	struct rw_semaphore lock; /* protect compression buffers and table
-				   * against concurrent read and writes */
+	struct rw_semaphore lock; /* protect compression buffers, table,
+				   * 32bit stat counters against concurrent
+				   * notifications, reads and writes */
 	struct request_queue *queue;
 	struct gendisk *disk;
 	int init_done;