On 8/20/21 8:08 AM, Christoph Hellwig wrote:
Please try the patch below:

---
From 7609266da56160d211662cd2fbe26570aad11b15 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <[email protected]>
Date: Fri, 20 Aug 2021 17:00:11 +0200
Subject: mtd_blkdevs: don't hold del_mtd_blktrans_dev in
  blktrans_{open,release}

There is nothing that this protects against except for slightly reducing
the window when new opens can appear just before calling del_gendisk.

Signed-off-by: Christoph Hellwig <[email protected]>

A cautious

Tested-by: Guenter Roeck <[email protected]>

Cautious because -next is a bit broken right now and I can not run a complete
test for all images.

Guenter

---
  drivers/mtd/mtd_blkdevs.c | 5 -----
  1 file changed, 5 deletions(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 44bea3f65060..6b81a1c9ccbe 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -207,7 +207,6 @@ static int blktrans_open(struct block_device *bdev, fmode_t 
mode)
        if (!dev)
                return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/
- mutex_lock(&mtd_table_mutex);
        mutex_lock(&dev->lock);
if (dev->open)
@@ -233,7 +232,6 @@ static int blktrans_open(struct block_device *bdev, fmode_t 
mode)
  unlock:
        dev->open++;
        mutex_unlock(&dev->lock);
-       mutex_unlock(&mtd_table_mutex);
        blktrans_dev_put(dev);
        return ret;
@@ -244,7 +242,6 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
        module_put(dev->tr->owner);
        kref_put(&dev->ref, blktrans_dev_release);
        mutex_unlock(&dev->lock);
-       mutex_unlock(&mtd_table_mutex);
        blktrans_dev_put(dev);
        return ret;
  }
@@ -256,7 +253,6 @@ static void blktrans_release(struct gendisk *disk, fmode_t 
mode)
        if (!dev)
                return;
- mutex_lock(&mtd_table_mutex);
        mutex_lock(&dev->lock);
if (--dev->open)
@@ -272,7 +268,6 @@ static void blktrans_release(struct gendisk *disk, fmode_t 
mode)
        }
  unlock:
        mutex_unlock(&dev->lock);
-       mutex_unlock(&mtd_table_mutex);
        blktrans_dev_put(dev);
  }

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