[lvm-devel] iSCSI logout hangs LVM

[Dave Wysochanski]

On Wed, 2009-01-14 at 22:23 -0700, Ty! Boyack wrote:
> Hi folks,
> 
> I'm not sure if I'm seeing a bug in LVM, device mapper (dm-multipath), 
> open-iscsi or udev, but this seems like the best place to start. 
> 
> 
> I can cause pvscan to hang consistently with the following sequence of 
> events:
> 1) run pvscan -- works OK
> 2) connect to iscsi disk -- works OK
> 3) run pvscan -- works OK, finds physical volume on iscsi disk
> 4) logout of iscsi disk -- works OK
> 5) run pvscan -- HANGS
> 
> 
> If I run the (step 5) pvscan with 'strace -f /sbin/pvscan' the end of 
> that trace is:
> 
> stat("/dev/dm-2", {st_mode=S_IFBLK|0660, st_rdev=makedev(253, 2), ...}) = 0
> stat("/dev/dm-2", {st_mode=S_IFBLK|0660, st_rdev=makedev(253, 2), ...}) = 0
> open("/dev/dm-2", O_RDWR|O_DIRECT|O_NOATIME) = 4
> fstat(4, {st_mode=S_IFBLK|0660, st_rdev=makedev(253, 2), ...}) = 0
> ioctl(4, BLKBSZGET, 0x20043f0)          = 0
> lseek(4, 12884836352, SEEK_SET)         = 12884836352
> read(4,
> 
> and then the read hangs forever.
> 
> In my setup, the iscsi login/logout is to a single target with two 
> portals, and dm-multipath us used to present one multi-path device.  
> That device in this case is /dev/dm-2.  I can use that disk as a PV just 
> fine -- it's in a VG and has a couple of LV's filled with test data.
> 
> I retried the sequence but only logged into one portal, so only one 
> connection existed (hopefully bypassing dm-multipath) and had exactly 
> the same problem.
> 
> I also tried waiting several minutes after logging out of the iSCSI disk 
> before running pvscan, and that also hang.
> 
> It seems like the LVM database detects a new disk being inserted, but 
> not removed.  I have not tried this on any other hot-swap disk system -- 
> has anyone tried this with a USB or other removable disk?
> 
> Does anyone know if this is expected behavior?  Or is it a problem 
> elsewhere, maybe with udev not doing something to indicate that the disk 
> has been removed?  Or does LVM keep it's own internal database of where 
> it's PV's are, and then later assume that they will still be there?
> 
> This is all being done on a Fedora 9 boxes with updated packages:
> lvm2-2.02.33-11.fc9.x86_64
> iscsi-initiator-utils-6.2.0.870-1.0.fc9.x86_64
> device-mapper-1.02.24-11.fc9.x86_64
> udev-124-2.fc9.x86_64
> kernel-2.6.27.9-73.fc9.x86_64
> 
> I would appreciate any thoughts or suggestion on this!
> 

You need to make sure iscsi and multipath are setup properly to
eventually fail the IO.  I believe the README and/or config files in
these projects describe the settings needed.