[PATCH 07/12] fs: stop using get_super in fs_mark_dead

Christoph Hellwig
2023-08-02T15:42:47Z

fs_mark_dead currently uses get_super to find the superblock for the
block device that is going away. This means it is limited to the
main device stored in sb->s_dev, leading to a lot of code duplication
for file systems that can use multiple block devices.

Now that the holder for all block devices used by file systems is set
to the super_block, we can instead look at that holder and then check
if the file system is born and active, so do that instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/super.c | 30 ++++++++++++++++++++++++++----
1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 09b65ee1a8b737..0cda4af0a7e16c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1209,17 +1209,39 @@ int get_tree_keyed(struct fs_context *fc,
EXPORT_SYMBOL(get_tree_keyed);

#ifdef CONFIG_BLOCK
+/*
+ * Lock a super block that the callers holds a reference to.
+ *
+ * The caller needs to ensure that the super_block isn't being freed while
+ * calling this function, e.g. by holding a lock over the call to this function
+ * and the place that clears the pointer to the superblock used by this function
+ * before freeing the superblock.
+ */
+static bool lock_active_super(struct super_block *sb)
+{
+ down_read(&sb->s_umount);
+ if (!sb->s_root ||
+ (sb->s_flags & (SB_ACTIVE | SB_BORN)) != (SB_ACTIVE | SB_BORN)) {
+ up_read(&sb->s_umount);
+ return false;
+ }
+ return true;
+}
+
static void fs_mark_dead(struct block_device *bdev)
{
- struct super_block *sb;
+ struct super_block *sb = bdev->bd_holder;

- sb = get_super(bdev);
- if (!sb)
+ /* bd_holder_lock ensures that the sb isn't freed */
+ lockdep_assert_held(&bdev->bd_holder_lock);
+
+ if (!lock_active_super(sb))
return;

if (sb->s_op->shutdown)
sb->s_op->shutdown(sb);
- drop_super(sb);
+
+ up_read(&sb->s_umount);
}

static const struct blk_holder_ops fs_holder_ops = {
--
2.39.2