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Date:   Thu, 1 Jul 2021 08:42:04 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Christian L?hle <CLoehle@hyperstone.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "axboe@kernel.dk" <axboe@kernel.dk>
Subject: Re: [PATCH] block: prevent sending events from removed device
Message-ID: <YN1xzGPbx8ac8r3j@infradead.org>
References: <CWXP265MB2680EBAF4FEE64FBE80FAF25C4019@CWXP265MB2680.GBRP265.PROD.OUTLOOK.COM>
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On Wed, Jun 30, 2021 at 08:09:39AM +0000, Christian L?hle wrote:
> Skip kobject_uevent_env in case the associated kobject
> no longer exists, as calling kobject_uevent_env with
> NULL is not safe.
> 

I don't see how this is going to work.  If the device is being
deleted the reference count will be zero and refcount_inc as
called from kobject_get will WARN.  We'll need to check the
disk is marked up, and we need to do that under a lock.

Something like this completely untested patch:

diff --git a/block/disk-events.c b/block/disk-events.c
index a75931ff5da4..27b845c51f2a 100644
--- a/block/disk-events.c
+++ b/block/disk-events.c
@@ -190,6 +190,9 @@ static void disk_check_events(struct disk_events *ev,
 
 	spin_unlock_irq(&ev->lock);
 
+	if (!(disk->flags & GENHD_FL_UP))
+		return;
+
 	/*
 	 * Tell userland about new events.  Only the events listed in
 	 * @disk->events are reported, and only if DISK_EVENT_FLAG_UEVENT
@@ -268,6 +271,8 @@ bool bdev_check_media_change(struct block_device *bdev)
 {
 	unsigned int events;
 
+	lockdep_assert_held(&bdev->bd_disk->open_mutex);
+
 	events = disk_clear_events(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE |
 				   DISK_EVENT_EJECT_REQUEST);
 	if (!(events & DISK_EVENT_MEDIA_CHANGE))
@@ -290,7 +295,10 @@ static void disk_events_workfn(struct work_struct *work)
 	struct delayed_work *dwork = to_delayed_work(work);
 	struct disk_events *ev = container_of(dwork, struct disk_events, dwork);
 
-	disk_check_events(ev, &ev->clearing);
+	mutex_lock(&ev->disk->open_mutex);
+	if (ev->disk->flags & GENHD_FL_UP)
+		disk_check_events(ev, &ev->clearing);
+	mutex_unlock(&ev->disk->open_mutex);
 }
 
 /*
diff --git a/drivers/block/ataflop.c b/drivers/block/ataflop.c
index a093644ac39f..b8e77da44235 100644
--- a/drivers/block/ataflop.c
+++ b/drivers/block/ataflop.c
@@ -1735,8 +1735,10 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode,
 		/* invalidate the buffer track to force a reread */
 		BufferDrive = -1;
 		set_bit(drive, &fake_change);
+		mutex_lock(&bdev->bd_disk->open_mutex);
 		if (bdev_check_media_change(bdev))
 			floppy_revalidate(bdev->bd_disk);
+		mutex_unlock(&bdev->bd_disk->open_mutex);
 		return 0;
 	default:
 		return -EINVAL;
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 87460e0e5c72..2a97f22cfa0b 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3185,8 +3185,10 @@ static int invalidate_drive(struct block_device *bdev)
 	/* invalidate the buffer track to force a reread */
 	set_bit((long)bdev->bd_disk->private_data, &fake_change);
 	process_fd_request();
+	mutex_lock(&bdev->bd_disk->open_mutex);
 	if (bdev_check_media_change(bdev))
 		floppy_revalidate(bdev->bd_disk);
+	mutex_unlock(&bdev->bd_disk->open_mutex);
 	return 0;
 }