Patch "zram: support BDI_CAP_STABLE_WRITES" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    zram: support BDI_CAP_STABLE_WRITES

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     zram-support-bdi_cap_stable_writes.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From b09ab054b69b07077bd3292f67e777861ac796e5 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Tue, 10 Jan 2017 16:58:21 -0800
Subject: zram: support BDI_CAP_STABLE_WRITES

From: Minchan Kim <minchan@kernel.org>

commit b09ab054b69b07077bd3292f67e777861ac796e5 upstream.

zram has used per-cpu stream feature from v4.7.  It aims for increasing
cache hit ratio of scratch buffer for compressing.  Downside of that
approach is that zram should ask memory space for compressed page in
per-cpu context which requires stricted gfp flag which could be failed.
If so, it retries to allocate memory space out of per-cpu context so it
could get memory this time and compress the data again, copies it to the
memory space.

In this scenario, zram assumes the data should never be changed but it is
not true without stable page support.  So, If the data is changed under
us, zram can make buffer overrun so that zsmalloc free object chain is
broken so system goes crash like below

   https://bugzilla.suse.com/show_bug.cgi?id=997574

This patch adds BDI_CAP_STABLE_WRITES to zram for declaring "I am block
device needing *stable write*".

Fixes: da9556a2367c ("zram: user per-cpu compression streams")
Link: http://lkml.kernel.org/r/1482366980-3782-4-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Hyeoncheol Lee <cheol.lee@lge.com>
Cc: <yjay.kim@lge.com>
Cc: Sangseok Lee <sangseok.lee@lge.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Darrick J. Wong <darrick.wong@oracle.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 |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -25,6 +25,7 @@
 #include <linux/genhd.h>
 #include <linux/highmem.h>
 #include <linux/slab.h>
+#include <linux/backing-dev.h>
 #include <linux/string.h>
 #include <linux/vmalloc.h>
 #include <linux/err.h>
@@ -111,6 +112,14 @@ static inline bool is_partial_io(struct
 	return bvec->bv_len != PAGE_SIZE;
 }
 
+static void zram_revalidate_disk(struct zram *zram)
+{
+	revalidate_disk(zram->disk);
+	/* revalidate_disk reset the BDI_CAP_STABLE_WRITES so set again */
+	zram->disk->queue->backing_dev_info.capabilities |=
+		BDI_CAP_STABLE_WRITES;
+}
+
 /*
  * Check if request is within bounds and aligned on zram logical blocks.
  */
@@ -1094,7 +1103,7 @@ 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);
+	zram_revalidate_disk(zram);
 	up_write(&zram->init_lock);
 
 	return len;
@@ -1142,7 +1151,7 @@ static ssize_t reset_store(struct device
 	/* Make sure all the pending I/O are finished */
 	fsync_bdev(bdev);
 	zram_reset_device(zram);
-	revalidate_disk(zram->disk);
+	zram_revalidate_disk(zram);
 	bdput(bdev);
 
 	mutex_lock(&bdev->bd_mutex);


Patches currently in stable-queue which might be from minchan@kernel.org are

queue-4.9/zram-support-bdi_cap_stable_writes.patch
queue-4.9/zram-revalidate-disk-under-init_lock.patch
queue-4.9/mm-pmd-dirty-emulation-in-page-fault-handler.patch