On Mon, 2017-03-06 at 13:01 +0100, Jan Kara wrote: > On Mon 06-03-17 11:27:33, Jan Kara wrote: > > Hi, > > > > On Sun 05-03-17 10:21:11, Wu Fengguang wrote: > > > FYI next-20170303 is good while mainline is bad with this error. > > > The attached reproduce-* may help reproduce the issue. > > > > Thanks for report! So from the stacktrace we are in the path > > testing removal of a device immediately after it has been probed > > and for some reason bdi_unregister() hangs - likely waiting for > > cgroup-writeback references to drop. Given how early this happens > > my guess is we fail to initialize something but for now I don't see > > how my patch could make a difference. I'm trying to reproduce this > > to be able to debug more... > > OK, so after some debugging I think this is yet another problem in > SCSI initialization / destruction code which my patch only makes > visible (added relevant maintainers). > > I can reproduce the problem reliably with enabling: > > CONFIG_DEBUG_TEST_DRIVER_REMOVE=y > CONFIG_SCSI_DEBUG=m > CONFIG_BLK_CGROUP=y > CONFIG_MEMCG=y > (and thus CONFIG_CGROUP_WRITEBACK=y) > > then 'modprobe scsi_debug' is all it takes to reproduce hang. > Relevant kernel messages with some of my debugging added (attached is > a patch that adds those debug messages):
This looks to be precisely the same problem Dan Williams was debugging for us. > [ 58.721765] scsi host0: scsi_debug: version 1.86 [20160430] > [ 58.721765] dev_size_mb=8, opts=0x0, submit_queues=1, > statistics=0 > [ 58.728946] CGWB init ffff88007fbb2000 > [ 58.730095] Created sdev ffff880078e1a000 > [ 58.731611] scsi 0:0:0:0: Direct-Access Linux scsi_debug > 0186 PQ : 0 ANSI: 7 > [ 58.782246] sd 0:0:0:0: [sda] 16384 512-byte logical blocks: (8.39 > MB/8.00 MiB) > [ 58.789687] sd 0:0:0:0: [sda] Write Protect is off > [ 58.791140] sd 0:0:0:0: [sda] Mode Sense: 73 00 10 08 > [ 58.800879] sd 0:0:0:0: [sda] Write cache: enabled, read cache: > enabled, supports DPO and FUA > [ 58.893738] sd 0:0:0:0: [sda] Attached SCSI disk > [ 58.896808] Unreg1 > [ 58.897960] Unreg2 > [ 58.898637] Unreg3 > [ 58.899100] CGWB ffff88007fbb2000 usage_cnt: 0 > [ 58.900004] Unreg4 > [ 58.904976] sd 0:0:0:0: [sda] Synchronizing SCSI cache OK, can you put a WARN_ON trace in sd_shutdown and tell us where this is coming from. For the device to be reused after this we have to be calling sd_shutdown() without going into SDEV_DEL. Thanks, James
