linux-kernel - [PATCH AUTOSEL 5.15 32/68] block: avoid to touch unloaded module instance when opening bdev

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Date:   Tue, 30 Nov 2021 09:46:28 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        czhong@...hat.com, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 32/68] block: avoid to touch unloaded module instance when opening bdev

From: Ming Lei <ming.lei@...hat.com>

[ Upstream commit efcf5932230b9472cfdbe01c858726f29ac5ec7d ]

disk->fops->owner is grabbed in blkdev_get_no_open() after the disk
kobject refcount is increased. This way can't make sure that
disk->fops->owner is still alive since del_gendisk() still can move
on if the kobject refcount of disk is grabbed by open() and
disk->fops->open() isn't called yet.

Fixes the issue by moving try_module_get() into blkdev_get_by_dev()
with ->open_mutex() held, then we can drain the in-progress open()
in del_gendisk(). Meantime new open() won't succeed because disk
becomes not alive.

This way is reasonable because blkdev_get_no_open() needn't to touch
disk->fops or defined callbacks.

Cc: Christoph Hellwig <hch@....de>
Cc: czhong@...hat.com
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Link: https://lore.kernel.org/r/20211111020343.316126-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/bdev.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index 485a258b0ab37..e52af269004bc 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -750,8 +750,7 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 
 	if (!bdev)
 		return NULL;
-	if ((bdev->bd_disk->flags & GENHD_FL_HIDDEN) ||
-	    !try_module_get(bdev->bd_disk->fops->owner)) {
+	if ((bdev->bd_disk->flags & GENHD_FL_HIDDEN)) {
 		put_device(&bdev->bd_device);
 		return NULL;
 	}
@@ -761,7 +760,6 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 
 void blkdev_put_no_open(struct block_device *bdev)
 {
-	module_put(bdev->bd_disk->fops->owner);
 	put_device(&bdev->bd_device);
 }
 
@@ -817,12 +815,14 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
 	ret = -ENXIO;
 	if (!disk_live(disk))
 		goto abort_claiming;
+	if (!try_module_get(disk->fops->owner))
+		goto abort_claiming;
 	if (bdev_is_partition(bdev))
 		ret = blkdev_get_part(bdev, mode);
 	else
 		ret = blkdev_get_whole(bdev, mode);
 	if (ret)
-		goto abort_claiming;
+		goto put_module;
 	if (mode & FMODE_EXCL) {
 		bd_finish_claiming(bdev, holder);
 
@@ -844,7 +844,8 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
 	if (unblock_events)
 		disk_unblock_events(disk);
 	return bdev;
-
+put_module:
+	module_put(disk->fops->owner);
 abort_claiming:
 	if (mode & FMODE_EXCL)
 		bd_abort_claiming(bdev, holder);
@@ -953,6 +954,7 @@ void blkdev_put(struct block_device *bdev, fmode_t mode)
 		blkdev_put_whole(bdev, mode);
 	mutex_unlock(&disk->open_mutex);
 
+	module_put(disk->fops->owner);
 	blkdev_put_no_open(bdev);
 }
 EXPORT_SYMBOL(blkdev_put);
-- 
2.33.0