Messages in this thread | | | Date | Thu, 12 Aug 2021 12:38:51 +0200 | From | David Sterba <> | Subject | Re: [PATCH v2] btrfs: fix rw device counting in __btrfs_free_extra_devids |
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On Tue, Jul 27, 2021 at 03:13:03PM +0800, Desmond Cheong Zhi Xi wrote: > 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 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 cf89af146b7e ("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 82372bc816d7 ("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. > > Fixes: cf89af146b7e ("btrfs: dev-replace: fail mount if we don't have replace item with target device") > Reported-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com > Tested-by: syzbot+a70e2ad0879f160b9217@syzkaller.appspotmail.com > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > Reviewed-by: Anand Jain <anand.jain@oracle.com> > --- > fs/btrfs/volumes.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 807502cd6510..916c25371658 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -1078,6 +1078,7 @@ static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, > if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) { > list_del_init(&device->dev_alloc_list); > clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state); > + fs_devices->rw_devices--; > } > list_del_init(&device->dev_list); > fs_devices->num_devices--;
I've hit a crash on master branch with stacktrace very similar to one this bug was supposed to fix. It's a failed assertion on device close. This patch was the last one to touch it and it matches some of the keywords, namely the BTRFS_DEV_STATE_REPLACE_TGT bit that used to be in the original patch but was not reinstated in your fix.
I'm not sure how reproducible it is, right now I have only one instance and am hunting another strange problem. They could be related.
assertion failed: !test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state), in fs/btrfs/volumes.c:1150
https://susepaste.org/view/raw/18223056 full log with other stacktraces, possibly relatedg
[ 3310.383268] kernel BUG at fs/btrfs/ctree.h:3431! [ 3310.384586] invalid opcode: 0000 [#1] PREEMPT SMP [ 3310.385848] CPU: 1 PID: 3982 Comm: umount Tainted: G W 5.14.0-rc5-default+ #1532 [ 3310.388216] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 [ 3310.391054] RIP: 0010:assertfail.constprop.0+0x18/0x1a [btrfs] [ 3310.397628] RSP: 0018:ffffb7a5454c7db8 EFLAGS: 00010246 [ 3310.399079] RAX: 0000000000000068 RBX: ffff978364b91c00 RCX: 0000000000000000 [ 3310.400990] RDX: 0000000000000000 RSI: ffffffffabee13c4 RDI: 00000000ffffffff [ 3310.402504] RBP: ffff9783523a4c00 R08: 0000000000000001 R09: 0000000000000001 [ 3310.404025] R10: 0000000000000000 R11: 0000000000000001 R12: ffff9783523a4d18 [ 3310.405074] R13: 0000000000000000 R14: 0000000000000004 R15: 0000000000000003 [ 3310.406130] FS: 00007f61c8f42800(0000) GS:ffff9783bd800000(0000) knlGS:0000000000000000 [ 3310.407649] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3310.409022] CR2: 000056190cffa810 CR3: 0000000030b96002 CR4: 0000000000170ea0 [ 3310.410111] Call Trace: [ 3310.410561] btrfs_close_one_device.cold+0x11/0x55 [btrfs] [ 3310.411788] close_fs_devices+0x44/0xb0 [btrfs] [ 3310.412654] btrfs_close_devices+0x48/0x160 [btrfs] [ 3310.413449] generic_shutdown_super+0x69/0x100 [ 3310.414155] kill_anon_super+0x14/0x30 [ 3310.414802] btrfs_kill_super+0x12/0x20 [btrfs] [ 3310.415767] deactivate_locked_super+0x2c/0xa0 [ 3310.416562] cleanup_mnt+0x144/0x1b0 [ 3310.417153] task_work_run+0x59/0xa0 [ 3310.417744] exit_to_user_mode_loop+0xe7/0xf0 [ 3310.418440] exit_to_user_mode_prepare+0xaf/0xf0 [ 3310.419425] syscall_exit_to_user_mode+0x19/0x50 [ 3310.420281] do_syscall_64+0x4a/0x90 [ 3310.420934] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 3310.421718] RIP: 0033:0x7f61c91654db
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