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The replace target device can be missing when mounted with -o degraded, but we wont allocate a missing btrfs_device to it. So check the device before accessing. BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0 IP: btrfs_destroy_dev_replace_tgtdev+0x43/0xf0 [btrfs] Call Trace: btrfs_dev_replace_cancel+0x15f/0x180 [btrfs] btrfs_ioctl+0x2216/0x2590 [btrfs] do_vfs_ioctl+0x625/0x650 SyS_ioctl+0x4e/0x80 do_syscall_64+0x5d/0x160 entry_SYSCALL64_slow_path+0x25/0x25 This patch has been moved in front of patch "btrfs: log, when replace, is canceled by the user" that could reproduce the crash if the system reboots inside btrfs_dev_replace_start before the btrfs_dev_replace_finishing call. $ mkfs /dev/sda $ mount /dev/sda mnt $ btrfs replace start /dev/sda /dev/sdb <insert reboot> $ mount po degraded /dev/sdb mnt <crash> Signed-off-by: Anand Jain <anand.jain@oracle.com> [ added reproducer description from mail ] Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.