linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: axboe@kernel.dk
Cc: Gulam Mohamed <gulam.mohamed@oracle.com>,
	Ming Lei <ming.lei@redhat.com>,
	linux-block@vger.kernel.org
Subject: [PATCH 1/2] block: prevent block device lookups at the beginning of del_gendisk
Date: Fri, 14 May 2021 15:18:41 +0200	[thread overview]
Message-ID: <20210514131842.1600568-2-hch@lst.de> (raw)
In-Reply-To: <20210514131842.1600568-1-hch@lst.de>

As an artifact of how gendisk lookup used to work in earlier kernels,
GENHD_FL_UP is only cleared very late in del_gendisk, and a global lock
is used to prevent opens from succeeding while del_gendisk is tearing
down the gendisk.  Switch to clearing the flag early and under bd_mutex
so that callers can use bd_mutex to stabilize the flag, which removes
the need for the global mutex.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/genhd.c         | 11 +----------
 fs/block_dev.c        | 15 +++++----------
 include/linux/genhd.h |  2 --
 3 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 39ca97b0edc6..9f8cb7beaad1 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -29,8 +29,6 @@
 
 static struct kobject *block_depr;
 
-DECLARE_RWSEM(bdev_lookup_sem);
-
 /* for extended dynamic devt allocation, currently only one major is used */
 #define NR_EXT_DEVT		(1 << MINORBITS)
 static DEFINE_IDA(ext_devt_ida);
@@ -609,13 +607,8 @@ void del_gendisk(struct gendisk *disk)
 	blk_integrity_del(disk);
 	disk_del_events(disk);
 
-	/*
-	 * Block lookups of the disk until all bdevs are unhashed and the
-	 * disk is marked as dead (GENHD_FL_UP cleared).
-	 */
-	down_write(&bdev_lookup_sem);
-
 	mutex_lock(&disk->part0->bd_mutex);
+	disk->flags &= ~GENHD_FL_UP;
 	blk_drop_partitions(disk);
 	mutex_unlock(&disk->part0->bd_mutex);
 
@@ -629,8 +622,6 @@ void del_gendisk(struct gendisk *disk)
 	remove_inode_hash(disk->part0->bd_inode);
 
 	set_capacity(disk, 0);
-	disk->flags &= ~GENHD_FL_UP;
-	up_write(&bdev_lookup_sem);
 
 	if (!(disk->flags & GENHD_FL_HIDDEN)) {
 		sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
diff --git a/fs/block_dev.c b/fs/block_dev.c
index eb265d72fce8..580bae995b87 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1298,6 +1298,9 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode)
 	struct gendisk *disk = bdev->bd_disk;
 	int ret = 0;
 
+	if (!(disk->flags & GENHD_FL_UP))
+		return -ENXIO;
+
 	if (!bdev->bd_openers) {
 		if (!bdev_is_partition(bdev)) {
 			ret = 0;
@@ -1332,8 +1335,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode)
 			whole->bd_part_count++;
 			mutex_unlock(&whole->bd_mutex);
 
-			if (!(disk->flags & GENHD_FL_UP) ||
-			    !bdev_nr_sectors(bdev)) {
+			if (!bdev_nr_sectors(bdev)) {
 				__blkdev_put(whole, mode, 1);
 				bdput(whole);
 				return -ENXIO;
@@ -1364,16 +1366,12 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 	struct block_device *bdev;
 	struct gendisk *disk;
 
-	down_read(&bdev_lookup_sem);
 	bdev = bdget(dev);
 	if (!bdev) {
-		up_read(&bdev_lookup_sem);
 		blk_request_module(dev);
-		down_read(&bdev_lookup_sem);
-
 		bdev = bdget(dev);
 		if (!bdev)
-			goto unlock;
+			return NULL;
 	}
 
 	disk = bdev->bd_disk;
@@ -1383,14 +1381,11 @@ struct block_device *blkdev_get_no_open(dev_t dev)
 		goto put_disk;
 	if (!try_module_get(bdev->bd_disk->fops->owner))
 		goto put_disk;
-	up_read(&bdev_lookup_sem);
 	return bdev;
 put_disk:
 	put_disk(disk);
 bdput:
 	bdput(bdev);
-unlock:
-	up_read(&bdev_lookup_sem);
 	return NULL;
 }
 
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 7e9660ea967d..6fc26f7bdf71 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -306,8 +306,6 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
 }
 #endif /* CONFIG_SYSFS */
 
-extern struct rw_semaphore bdev_lookup_sem;
-
 dev_t blk_lookup_devt(const char *name, int partno);
 void blk_request_module(dev_t devt);
 #ifdef CONFIG_BLOCK
-- 
2.30.2


  reply	other threads:[~2021-05-14 13:18 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-14 13:18 fix a race between del_gendisk and BLKRRPART v2 Christoph Hellwig
2021-05-14 13:18 ` Christoph Hellwig [this message]
2021-05-15  6:34   ` [PATCH 1/2] block: prevent block device lookups at the beginning of del_gendisk Ming Lei
2021-05-20 17:37     ` Gulam Mohamed
2021-05-14 13:18 ` [PATCH 2/2] block: fix a race between del_gendisk and BLKRRPART Christoph Hellwig
2021-05-15  6:35   ` Ming Lei
2021-05-20 17:37     ` Gulam Mohamed
2021-05-20  8:14 ` fix a race between del_gendisk and BLKRRPART v2 Christoph Hellwig
2021-05-20 13:59   ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2021-05-12 16:50 fix a race between del_gendisk and BLKRRPART Christoph Hellwig
2021-05-12 16:50 ` [PATCH 1/2] block: prevent block device lookups at the beginning of del_gendisk Christoph Hellwig
2021-05-13  0:11   ` Ming Lei

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210514131842.1600568-2-hch@lst.de \
    --to=hch@lst.de \
    --cc=axboe@kernel.dk \
    --cc=gulam.mohamed@oracle.com \
    --cc=linux-block@vger.kernel.org \
    --cc=ming.lei@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).