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Syzbot reported a circular locking dependency: https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb This happens because of the following lock dependencies: 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls loop_remove, which then calls del_gendisk; this also happens in loop_exit which eventually calls loop_remove) 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls __blkdev_get, which then calls blktrans_open) 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans calls __register_blkdev) 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls loop_probe) Hence there's an overall dependency of: loop_ctl_mutex ----------> bdev->bd_mutex ^ | | | | v major_names_lock <--------- mtd_table_mutex We can break this circular dependency by holding mtd_table_mutex only for the required critical section in register_mtd_blktrans. This avoids the mtd_table_mutex -> major_names_lock dependency. Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com Co-developed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com> Link: https://lore.kernel.org/linux-mtd/20210617160904.570111-1-desmondcheongzx@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.