From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: [PATCHv4 09/10] zram: close race by open overriding
Date: Mon, 4 May 2015 21:39:01 +0900 [thread overview]
Message-ID: <1430743142-15854-10-git-send-email-sergey.senozhatsky@gmail.com> (raw)
In-Reply-To: <1430743142-15854-1-git-send-email-sergey.senozhatsky@gmail.com>
From: Minchan Kim <minchan@kernel.org>
[1] introduced bdev->bd_mutex to protect a race between mount
and reset. At that time, we don't have dynamic zram-add/remove
feature so it was okay.
However, as we introduce dynamic device feature, bd_mutex became
trouble.
CPU 0
echo 1 > /sys/block/zram<id>/reset
-> kernfs->s_active(A)
-> zram:reset_store->bd_mutex(B)
CPU 1
echo <id> > /sys/class/zram/zram-remove
->zram:zram_remove: bd_mutex(B)
-> sysfs_remove_group
-> kernfs->s_active(A)
IOW, AB -> BA deadlock
The reason we are holding bd_mutex for zram_remove is to prevent
any incoming open /dev/zram[0-9]. Otherwise, we could remove zram
others already have opened. But it causes above deadlock problem.
To fix the problem, this patch overrides block_device.open and
it returns -EBUSY if zram asserts he claims zram to reset so any
incoming open will be failed so we don't need to hold bd_mutex
for zram_remove ayn more.
This patch is to prepare for zram-add/remove feature.
[1] ba6b17: zram: fix umount-reset_store-mount race condition
[Sergey: simplify reset_store()]
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
drivers/block/zram/zram_drv.c | 53 +++++++++++++++++++++++++++----------------
drivers/block/zram/zram_drv.h | 4 ++++
2 files changed, 38 insertions(+), 19 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3df4394..b3541df 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1068,45 +1068,60 @@ static ssize_t reset_store(struct device *dev,
struct zram *zram;
struct block_device *bdev;
+ ret = kstrtou16(buf, 10, &do_reset);
+ if (ret)
+ return ret;
+
+ if (!do_reset)
+ return -EINVAL;
+
zram = dev_to_zram(dev);
bdev = bdget_disk(zram->disk, 0);
-
if (!bdev)
return -ENOMEM;
mutex_lock(&bdev->bd_mutex);
- /* Do not reset an active device! */
- if (bdev->bd_openers) {
- ret = -EBUSY;
- goto out;
+ /* Do not reset an active device or claimed device */
+ if (bdev->bd_openers || zram->claim) {
+ mutex_unlock(&bdev->bd_mutex);
+ bdput(bdev);
+ return -EBUSY;
}
- ret = kstrtou16(buf, 10, &do_reset);
- if (ret)
- goto out;
-
- if (!do_reset) {
- ret = -EINVAL;
- goto out;
- }
+ /* From now on, anyone can't open /dev/zram[0-9] */
+ zram->claim = true;
+ mutex_unlock(&bdev->bd_mutex);
- /* Make sure all pending I/O is finished */
+ /* Make sure all the pending I/O are finished */
fsync_bdev(bdev);
zram_reset_device(zram);
-
- mutex_unlock(&bdev->bd_mutex);
revalidate_disk(zram->disk);
bdput(bdev);
+ mutex_lock(&bdev->bd_mutex);
+ zram->claim = false;
+ mutex_unlock(&bdev->bd_mutex);
+
return len;
+}
+
+static int zram_open(struct block_device *bdev, fmode_t mode)
+{
+ int ret = 0;
+ struct zram *zram;
+
+ WARN_ON(!mutex_is_locked(&bdev->bd_mutex));
+
+ zram = bdev->bd_disk->private_data;
+ /* zram was claimed to reset so open request fails */
+ if (zram->claim)
+ ret = -EBUSY;
-out:
- mutex_unlock(&bdev->bd_mutex);
- bdput(bdev);
return ret;
}
static const struct block_device_operations zram_devops = {
+ .open = zram_open,
.swap_slot_free_notify = zram_slot_free_notify,
.rw_page = zram_rw_page,
.owner = THIS_MODULE
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 042994e..6dbe2df 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -115,5 +115,9 @@ struct zram {
*/
u64 disksize; /* bytes */
char compressor[10];
+ /*
+ * zram is claimed so open request will be failed
+ */
+ bool claim; /* Protected by bdev->bd_mutex */
};
#endif
--
2.4.0
next prev parent reply other threads:[~2015-05-04 12:41 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-04 12:38 [PATCHv4 00/10] add on-demand device creation Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 01/10] zram: add `compact` sysfs entry to documentation Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 02/10] zram: cosmetic ZRAM_ATTR_RO code formatting tweak Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 03/10] zram: use idr instead of `zram_devices' array Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 04/10] zram: reorganize code layout Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 05/10] zram: remove max_num_devices limitation Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 06/10] zram: report every added and removed device Sergey Senozhatsky
2015-05-04 12:38 ` [PATCHv4 07/10] zram: trivial: correct flag operations comment Sergey Senozhatsky
2015-05-04 12:39 ` [PATCHv4 08/10] zram: return zram device_id from zram_add() Sergey Senozhatsky
2015-05-04 12:39 ` Sergey Senozhatsky [this message]
2015-05-04 12:39 ` [PATCHv4 10/10] zram: add dynamic device add/remove functionality Sergey Senozhatsky
2015-05-06 5:01 ` [PATCHv4 00/10] add on-demand device creation Minchan Kim
2015-05-06 5:25 ` Sergey Senozhatsky
2015-05-06 6:52 ` Minchan Kim
2015-05-06 7:07 ` Sergey Senozhatsky
2015-05-06 7:28 ` Minchan Kim
2015-05-06 8:10 ` Sergey Senozhatsky
2015-05-06 8:20 ` Minchan Kim
2015-05-07 0:33 ` Sergey Senozhatsky
2015-05-07 7:41 ` Minchan Kim
2015-05-07 12:09 ` Sergey Senozhatsky
2015-05-07 13:04 ` Sergey Senozhatsky
2015-05-07 15:11 ` Minchan Kim
2015-05-08 0:15 ` Sergey Senozhatsky
2015-05-10 8:47 ` Sergey Senozhatsky
2015-05-06 5:31 ` Sergey Senozhatsky
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