[PATCH 3.15 16/37] zram: avoid lockdep splat by revalidate_disk

Greg Kroah-Hartman
2014-07-30T01:48:52Z

From: Minchan Kim <minchan@kernel.org>

commit b4c5c60920e3b0c4598f43e7317559f6aec51531 upstream.

Sasha reported lockdep warning [1] introduced by [2].

It could be fixed by doing disk revalidation out of the init_lock. It's
okay because disk capacity change is protected by init_lock so that
revalidate_disk always sees up-to-date value so there is no race.

[1] https://lkml.org/lkml/2014/7/3/735
[2] zram: revalidate disk after capacity change

Fixes 2e32baea46ce ("zram: revalidate disk after capacity change").

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: "Alexander E. Patrakov" <patrakov@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/zram/zram_drv.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -622,11 +622,18 @@ static void zram_reset_device(struct zra
memset(&zram->stats, 0, sizeof(zram->stats));

zram->disksize = 0;
- if (reset_capacity) {
+ if (reset_capacity)
set_capacity(zram->disk, 0);
- revalidate_disk(zram->disk);
- }
+
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,
@@ -666,8 +673,15 @@ static ssize_t disksize_store(struct dev
zram->comp = comp;
zram->disksize = disksize;
set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
- revalidate_disk(zram->disk);
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.
+ */
+ revalidate_disk(zram->disk);
+
return len;