The patch titled
Subject: zram: fix umount-reset_store-mount race condition
has been added to the -mm tree. Its filename is
zram-fix-umount-reset_store-mount-race-condition.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/zram-fix-umount-reset_store-mount-race-condition.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/zram-fix-umount-reset_store-mount-race-condition.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Subject: zram: fix umount-reset_store-mount race condition
Ganesh Mahendran was the first one who proposed to use bdev->bd_mutex to
avoid ->bd_holders race condition:
CPU0 CPU1
umount /* zram->init_done is true */
reset_store()
bdev->bd_holders == 0 mount
... zram_make_request()
zram_reset_device()
However, his solution required some considerable amount of code movement,
which we can avoid.
Apart from using bdev->bd_mutex in reset_store(), this patch also
simplifies zram_reset_device().
zram_reset_device() has a bool parameter reset_capacity which tells it
whether disk capacity and itself disk should be reset. There are two
zram_reset_device() callers:
-- zram_exit() passes reset_capacity=false
-- reset_store() passes reset_capacity=true
So we can move reset_capacity-sensitive work out of zram_reset_device()
and perform it unconditionally in reset_store(). This also lets us drop
reset_capacity parameter from zram_reset_device() and pass zram pointer
only.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Reported-by: Ganesh Mahendran <opensource.ganesh@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 23 +++++++++--------------
1 file changed, 9 insertions(+), 14 deletions(-)
diff -puN drivers/block/zram/zram_drv.c~zram-fix-umount-reset_store-mount-race-condition drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c~zram-fix-umount-reset_store-mount-race-condition
+++ a/drivers/block/zram/zram_drv.c
@@ -715,7 +715,7 @@ static void zram_bio_discard(struct zram
}
}
-static void zram_reset_device(struct zram *zram, bool reset_capacity)
+static void zram_reset_device(struct zram *zram)
{
down_write(&zram->init_lock);
@@ -734,18 +734,7 @@ static void zram_reset_device(struct zra
memset(&zram->stats, 0, sizeof(zram->stats));
zram->disksize = 0;
- if (reset_capacity)
- set_capacity(zram->disk, 0);
-
up_write(&zram->init_lock);
-
- /*
- * Revalidate disk out of the init_lock to avoid lockdep splat.
- * It's okay because disk's capacity is protected by init_lock
- * so that revalidate_disk always sees up-to-date capacity.
- */
- if (reset_capacity)
- revalidate_disk(zram->disk);
}
static ssize_t disksize_store(struct device *dev,
@@ -818,6 +807,7 @@ static ssize_t reset_store(struct device
if (!bdev)
return -ENOMEM;
+ mutex_lock(&bdev->bd_mutex);
/* Do not reset an active device! */
if (bdev->bd_holders) {
ret = -EBUSY;
@@ -835,12 +825,17 @@ static ssize_t reset_store(struct device
/* Make sure all pending I/O is finished */
fsync_bdev(bdev);
+ zram_reset_device(zram);
+ set_capacity(zram->disk, 0);
+
+ mutex_unlock(&bdev->bd_mutex);
+ revalidate_disk(zram->disk);
bdput(bdev);
- zram_reset_device(zram, true);
return len;
out:
+ mutex_unlock(&bdev->bd_mutex);
bdput(bdev);
return ret;
}
@@ -1186,7 +1181,7 @@ static void __exit zram_exit(void)
* Shouldn't access zram->disk after destroy_device
* because destroy_device already released zram->disk.
*/
- zram_reset_device(zram, false);
+ zram_reset_device(zram);
}
unregister_blkdev(zram_major, "zram");
_
Patches currently in -mm which might be from sergey.senozhatsky@xxxxxxxxx are
zram-clean-up-zram_meta_alloc.patch
zram-free-meta-table-in-zram_meta_free.patch
zram-fix-umount-reset_store-mount-race-condition.patch
linux-next.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
