Messages in this thread | | | From | Miquel Raynal <> | Subject | Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans | Date | Fri, 16 Jul 2021 00:50:40 +0200 |
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On Thu, 2021-06-17 at 16:09:04 UTC, Desmond Cheong Zhi Xi wrote: > 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>
Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.
Miquel
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