On Thu, Feb 11, 2021 at 06:11:39PM +0100, Ahmad Fatoum wrote:
> The VFS layer already increase the mount reference count for the mount
> point. This means e.g. following sequence is well-behaving:
>
> mkdir -p /mnt/disk0.0/media
> mount -o loop backing.squashfs /mnt/disk0.0/media
> umount /mnt/disk0.0
>
> barebox will do the right thing and report
>
> umount: Device or resource busy
>
> However the reference count of the file where backing.squashfs comes
> from is not incremented on mount with the effect that following sequence
> crashes:
>
> mkdir -p /media
> mount -o loop /mnt/disk0.0/backing.squashfs /media
> umount /mnt/disk0.0 # should've returned EBUSY
> umount /media
>
> Fix this by touching the backing store's mount reference count when
> loop mounting and unmounting.
>
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> fs/fs.c | 38 +++++++++++++++++++++++++++++++++-----
> 1 file changed, 33 insertions(+), 5 deletions(-)
>
> diff --git a/fs/fs.c b/fs/fs.c
> index 00b8645fb0e9..10cc08fc93ab 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -89,7 +89,13 @@ static int init_fs(void)
>
> postcore_initcall(init_fs);
>
> +struct filename;
> +
> static struct fs_device_d *get_fsdevice_by_path(const char *path);
> +static int filename_lookup(int dfd, struct filename *name, unsigned flags,
> + struct path *path);;
> +static struct filename *getname(const char *filename);
> +static void path_put(const struct path *path);
>
> LIST_HEAD(fs_device_list);
>
> @@ -683,6 +689,8 @@ static void fs_remove(struct device_d *dev)
> struct fs_device_d *fsdev = dev_to_fs_device(dev);
> struct super_block *sb = &fsdev->sb;
> struct inode *inode, *tmp;
> + struct path path;
> + int ret;
>
> if (fsdev->dev.driver) {
> dev->driver->remove(dev);
> @@ -695,9 +703,17 @@ static void fs_remove(struct device_d *dev)
> if (fsdev->cdev)
> cdev_close(fsdev->cdev);
>
> - if (fsdev->loop && fsdev->cdev)
> + if (fsdev->loop && fsdev->cdev) {
> cdev_remove_loop(fsdev->cdev);
>
> + ret = filename_lookup(AT_FDCWD, getname(fsdev->backingstore),
> + LOOKUP_FOLLOW, &path);
> + if (!ret) {
> + mntput(path.mnt);
> + path_put(&path);
> + }
> + }
> +
> if (fsdev->vfsmount.mountpoint)
> fsdev->vfsmount.mountpoint->d_flags &= ~DCACHE_MOUNTED;
>
> @@ -767,17 +783,29 @@ static const char *detect_fs(const char *filename, const char *fsoptions)
> int fsdev_open_cdev(struct fs_device_d *fsdev)
> {
> unsigned long long offset = 0;
> + struct path path = {};
> + int ret;
>
> parseopt_b(fsdev->options, "loop", &fsdev->loop);
> parseopt_llu_suffix(fsdev->options, "offset", &offset);
> - if (fsdev->loop)
> - fsdev->cdev = cdev_create_loop(fsdev->backingstore, O_RDWR,
> - offset);
> - else
> + if (fsdev->loop) {
> + ret = filename_lookup(AT_FDCWD, getname(fsdev->backingstore),
> + LOOKUP_FOLLOW, &path);
> + if (ret)
> + return ret;
> +
> + fsdev->cdev = cdev_create_loop(fsdev->backingstore, O_RDWR, offset);
> + } else {
> fsdev->cdev = cdev_open(fsdev->backingstore, O_RDWR);
> + }
> if (!fsdev->cdev)
> return -EINVAL;
path_put() is missing in this error path.
Sascha
--
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