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From:   Minchan Kim <minchan@kernel.org>
To:     stable@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>, hare@suse.com,
        LKML <linux-kernel@vger.kernel.org>, sashal@kernel.org,
        Minchan Kim <minchan@kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Howard Chen <howardsoc@google.com>
Subject: [PATCH] [PATCH for v3.18] zram: close udev startup race condition as default groups
Date:   Fri, 23 Nov 2018 15:30:22 +0900
Message-Id: <20181123063022.228315-1-minchan@kernel.org>
In-Reply-To: <20181115174504.GJ95254@sasha-vm>
References: <20181115174504.GJ95254@sasha-vm>
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Sender: linux-kernel-owner@vger.kernel.org
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commit fef912bf860e upstream.
commit 98af4d4df889 upstream.

I got a report from Howard Chen that he saw zram and sysfs race(ie,
zram block device file is created but sysfs for it isn't yet)
when he tried to create new zram devices via hotadd knob.

v4.20 kernel fixes it by [1, 2] but it's too large size to merge
into -stable so this patch fixes the problem by registering defualt
group by Greg KH's approach[3].

This patch should be applied to every stable tree [3.16+] currently
existing from kernel.org because the problem was introduced at 2.6.37
by [4].

[1] fef912bf860e, block: genhd: add 'groups' argument to device_add_disk
[2] 98af4d4df889, zram: register default groups with device_add_disk()
[3] http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/
[4] 33863c21e69e9, Staging: zram: Replace ioctls with sysfs interface

Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Hannes Reinecke <hare@suse.com>
Tested-by: Howard Chen <howardsoc@google.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/block/zram/zram_drv.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7e94459a489a..5f4e6a3c2dde 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -999,6 +999,11 @@ static struct attribute_group zram_disk_attr_group = {
 	.attrs = zram_disk_attrs,
 };
 
+static const struct attribute_group *zram_disk_attr_groups[] = {
+	&zram_disk_attr_group,
+	NULL,
+};
+
 static int create_device(struct zram *zram, int device_id)
 {
 	int ret = -ENOMEM;
@@ -1060,22 +1065,14 @@ static int create_device(struct zram *zram, int device_id)
 		zram->disk->queue->limits.discard_zeroes_data = 0;
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);
 
+	disk_to_dev(zram->disk)->groups = zram_disk_attr_groups;
 	add_disk(zram->disk);
 
-	ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
-				&zram_disk_attr_group);
-	if (ret < 0) {
-		pr_warn("Error creating sysfs group");
-		goto out_free_disk;
-	}
 	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
 	zram->meta = NULL;
 	zram->max_comp_streams = 1;
 	return 0;
 
-out_free_disk:
-	del_gendisk(zram->disk);
-	put_disk(zram->disk);
 out_free_queue:
 	blk_cleanup_queue(zram->queue);
 out:
@@ -1084,9 +1081,6 @@ static int create_device(struct zram *zram, int device_id)
 
 static void destroy_device(struct zram *zram)
 {
-	sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
-			&zram_disk_attr_group);
-
 	del_gendisk(zram->disk);
 	put_disk(zram->disk);
 
-- 
2.20.0.rc0.387.gc7a69e6b6c-goog