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 commit cf89af146b ("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 commit 82372bc816 ("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>
b2a6166768