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When removing a writeable device in __btrfs_free_extra_devids, the rw device count should be decremented. This error was caught by Syzbot which reported a warning in close_fs_devices: WARNING: CPU: 1 PID: 9355 at fs/btrfs/volumes.c:1168 close_fs_devices+0x763/0x880 fs/btrfs/volumes.c:1168 Modules linked in: CPU: 0 PID: 9355 Comm: syz-executor552 Not tainted 5.13.0-rc1-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:close_fs_devices+0x763/0x880 fs/btrfs/volumes.c:1168 RSP: 0018:ffffc9000333f2f0 EFLAGS: 00010293 RAX: ffffffff8365f5c3 RBX: 0000000000000001 RCX: ffff888029afd4c0 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 RBP: ffff88802846f508 R08: ffffffff8365f525 R09: ffffed100337d128 R10: ffffed100337d128 R11: 0000000000000000 R12: dffffc0000000000 R13: ffff888019be8868 R14: 1ffff1100337d10d R15: 1ffff1100337d10a FS: 00007f6f53828700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000047c410 CR3: 00000000302a6000 CR4: 00000000001506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: btrfs_close_devices+0xc9/0x450 fs/btrfs/volumes.c:1180 open_ctree+0x8e1/0x3968 fs/btrfs/disk-io.c:3693 btrfs_fill_super fs/btrfs/super.c:1382 [inline] btrfs_mount_root+0xac5/0xc60 fs/btrfs/super.c:1749 legacy_get_tree+0xea/0x180 fs/fs_context.c:592 vfs_get_tree+0x86/0x270 fs/super.c:1498 fc_mount fs/namespace.c:993 [inline] vfs_kern_mount+0xc9/0x160 fs/namespace.c:1023 btrfs_mount+0x3d3/0xb50 fs/btrfs/super.c:1809 legacy_get_tree+0xea/0x180 fs/fs_context.c:592 vfs_get_tree+0x86/0x270 fs/super.c:1498 do_new_mount fs/namespace.c:2905 [inline] path_mount+0x196f/0x2be0 fs/namespace.c:3235 do_mount fs/namespace.c:3248 [inline] __do_sys_mount fs/namespace.c:3456 [inline] __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae Because fs_devices->rw_devices was not 0 after closing all devices. Here is the call trace that was observed: btrfs_mount_root(): btrfs_scan_one_device(): device_list_add(); <---------------- device added btrfs_open_devices(): open_fs_devices(): btrfs_open_one_device(); <-------- writable device opened, rw device count ++ btrfs_fill_super(): open_ctree(): btrfs_free_extra_devids(): __btrfs_free_extra_devids(); <--- writable device removed, rw device count not decremented fail_tree_roots: btrfs_close_devices(): close_fs_devices(); <------- rw device count off by 1 As a note, prior to commitcf89af146b("btrfs: dev-replace: fail mount if we don't have replace item with target device"), rw_devices was decremented on removing a writable device in __btrfs_free_extra_devids only if the BTRFS_DEV_STATE_REPLACE_TGT bit was not set for the device. However, this check does not need to be reinstated as it is now redundant and incorrect. In __btrfs_free_extra_devids, we skip removing the device if it is the target for replacement. This is done by checking whether device->devid == BTRFS_DEV_REPLACE_DEVID. Since BTRFS_DEV_STATE_REPLACE_TGT is set only on the device with devid BTRFS_DEV_REPLACE_DEVID, no devices should have the BTRFS_DEV_STATE_REPLACE_TGT bit set after the check, and so it's redundant to test for that bit. Additionally, following commit82372bc816("Btrfs: make the logic of source device removing more clear"), rw_devices is incremented whenever a writeable device is added to the alloc list (including the target device in btrfs_dev_replace_finishing), so all removals of writable devices from the alloc list should also be accompanied by a decrement to rw_devices. Reported-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com Fixes:cf89af146b("btrfs: dev-replace: fail mount if we don't have replace item with target device") CC: stable@vger.kernel.org # 5.10+ Tested-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Signed-off-by: David Sterba <dsterba@suse.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.