In our case, there is a mountpoint of ceph-fuse type and this mountpoint 
is abnormal.
I execute 'xfs_repair -n /dev/nbd4' cmd. Then xfs_repair is blocked in 
stat()
systemcall. '/dev/nbd4' has no relationship with the ceph-fuse mountpoint.

[root@compute5 ~]# ps aux | grep xfs_repair
root     16469  0.0  0.0 114744   564 ?        D    10:50   0:00 
xfs_repair -n /dev/nbd4

[root@compute5 ~]# cat /proc/16469/stack
[<ffffffffa04b953d>] __fuse_request_send+0x13d/0x2c0 [fuse]
[<ffffffffa04b96d2>] fuse_request_send+0x12/0x20 [fuse]
[<ffffffffa04be67a>] fuse_do_getattr+0x11a/0x2e0 [fuse]
[<ffffffffa04bfba5>] fuse_update_attributes+0x75/0x80 [fuse]
[<ffffffffa04bfbf3>] fuse_getattr+0x43/0x50 [fuse]
[<ffffffff81203976>] vfs_getattr+0x46/0x80
[<ffffffff81203aa5>] vfs_fstatat+0x75/0xc0
[<ffffffff81203ffe>] SYSC_newstat+0x2e/0x60
[<ffffffff812042de>] SyS_newstat+0xe/0x10
[<ffffffff81697809>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

The stat() is from the following code:

// libxfs/linux.c:platform_check_mount()
   while ((mnt = getmntent(f)) != NULL) {
     if (stat64(mnt->mnt_fsname, &mst) < 0) <---------<<<< 
unconditionally stat all mountpoints
       continue;

xfs_repair have to check all mountpoints of the system to make sure 
there is
no writable mount point of user specified device. If there is one abnormal
mountpoint, event it not related to user specified device, xfs_repair will
be blocked.

I can make sure there is no writable mountpoint of /dev/nbd4, so xfs_repair
don't need to check all mountpoints of the system. This is why I want to add
this '-F' option.

Because there are lots of other services on this node, I can't reboot 
the machine.

thx

Yang Honggang

On 02/25/2018 06:04 AM, Dave Chinner wrote:

On Sat, Feb 24, 2018 at 11:56:44AM -0600, Eric Sandeen wrote:

quoted

On 2/24/18 5:23 AM, Yang Joseph wrote:

quoted

hello,

Before the repair process, xfs_repair will check if user specified device already
has a writable mountpoint. And it will stat all the mountpoints of the system. If there
is a dead mountpoint, this checking will be blocked and xfs_repair will enter 'D' state.

So why is the mount point dead?

That kinda means that the filesystem is still mounted, but something
has hung somewhere and the filesystem may still have active
references to the underlying device and be doing stuff that is
modifying the filesystem....

And if the device is still busy, then you aren't going to be able to
mount the repaired device, anyway, because the block device is still
busy...

quoted

That sounds like a bug worth fixing, but I am much
less excited about adding options which could do serious damage
to a filesystem.

TO me it sounds like something that should be fixed by a reboot, not
by adding dangerous options to xfs_repair...

Cheers,

Dave.