From 8c54499a59b026a3dc2afccf6e1b36d5700d2fef Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Mon, 25 Oct 2021 10:54:24 +0800
Subject: [PATCH] zram: don't fail to remove zram during unloading module
Git-commit: 8c54499a59b026a3dc2afccf6e1b36d5700d2fef
Reviewed-by: Luis Chamberlain <mcgrof@suse.com>
Patch-mainline: v5.16-rc1
References: bsc#1170269

When the zram module is being unloaded, no one should be using the
zram disks. However even while being unloaded the zram module's
sysfs attributes might be poked at to re-configure zram devices.
This is expected, and kernfs ensures that these operations complete
before device_del() completes.

But reset_store() may set ->claim which will fail zram_remove(), when
this happens, zram_reset_device() is bypassed, and zram->comp can't
be destroyed, so the warning of 'Error: Removing state 63 which has
instances left.' is triggered during unloading module, together with
memory leak and sort of thing.

Fixes the issue by not failing zram_remove() if ->claim is set, and
we actually need to do nothing in case that zram_reset() is running
since del_gendisk() will wait until zram_reset() is done.

Reported-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Link: https://lore.kernel.org/r/20211025025426.2815424-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 drivers/block/zram/zram_drv.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 313e093..b12694c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1966,31 +1966,46 @@ static int zram_add(void)
 static int zram_remove(struct zram *zram)
 {
 	struct block_device *bdev;
+	bool claimed;
 
 	bdev = bdget_disk(zram->disk, 0);
 	if (!bdev)
 		return -ENOMEM;
 
 	mutex_lock(&bdev->bd_mutex);
-	if (bdev->bd_openers || zram->claim) {
+	if (bdev->bd_openers) {
 		mutex_unlock(&bdev->bd_mutex);
 		bdput(bdev);
 		return -EBUSY;
 	}
 
-	zram->claim = true;
+	claimed = zram->claim;
+	if (!claimed)
+		zram->claim = true;
 	mutex_unlock(&bdev->bd_mutex);
 
 	zram_debugfs_unregister(zram);
 
+	if (claimed) {
+		/*
+		 * If we were claimed by reset_store(), del_gendisk() will
+		 * wait until reset_store() is done, so nothing need to do.
+		 */
+		;
+	} else {
 	/* Make sure all the pending I/O are finished */
-	fsync_bdev(bdev);
-	zram_reset_device(zram);
-	bdput(bdev);
+		fsync_bdev(bdev);
+		zram_reset_device(zram);
+		bdput(bdev);
+	}
 
 	pr_info("Removed device: %s\n", zram->disk->disk_name);
 
 	del_gendisk(zram->disk);
+
+	/* del_gendisk drains pending reset_store */
+	WARN_ON_ONCE(claimed && zram->claim);
+
 	blk_cleanup_queue(zram->disk->queue);
 	put_disk(zram->disk);
 	kfree(zram);
@@ -2068,7 +2083,7 @@ static struct class zram_control_class = {
 
 static int zram_remove_cb(int id, void *ptr, void *data)
 {
-	zram_remove(ptr);
+	WARN_ON_ONCE(zram_remove(ptr));
 	return 0;
 }