Re: kern/46462: Hang trying to run a disklabel on an inserted USB flash drive

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sat, May 19, 2012 at 08:29:03PM +0100, Mindaugas Rasiukevicius wrote:
> OK, this thread is likely a problem:
> 
> > db> tr/t 0.59
> > trace: pid 0 lid 59 at 0xffffa00049c1b770
> > sleepq_block() at netbsd:sleepq_block+0xdd
> > cv_wait() at netbsd:cv_wait+0xf1
> > biowait() at netbsd:biowait+0x4f
> > read_sector() at netbsd:read_sector+0x23
> > scan_mbr() at netbsd:scan_mbr+0x40
> > readdisklabel() at netbsd:readdisklabel+0xfb
> > sdopen() at netbsd:sdopen+0x26a
> > spec_open() at netbsd:spec_open+0x29a
> > VOP_OPEN() at netbsd:VOP_OPEN+0x29
> > dkwedge_discover() at netbsd:dkwedge_discover+0xee
> > sdattach() at netbsd:sdattach+0x206
> > config_attach_loc() at netbsd:config_attach_loc+0x15a
> > scsi_probe_bus() at netbsd:scsi_probe_bus+0x4aa
> > scsibus_config() at netbsd:scsibus_config+0x5d
> > scsipi_completion_thread() at netbsd:scsipi_completion_thread+0x23
> 
> - scsipi_completion_thread()
>       This asynchronous completion thread handles the event, which is
>       in this case attaching of a new device.  Callbacks are performed
>       under splbio().
> 
> -- [skipping] .. sdopen()
>       Acquiring sd->sc_dk.dk_openlock here.  We are still at IPL_BIO.
> 
> --- [skipping] .. read_sector() -> disk_read_sectors()
>       Invoking sdstrategy() and entering biowait().  However, since
>       we are still at IPL_BIO, biodone() does not happen - thread has
>       deadlocked against interrupt with sd->sc_dk.dk_openlock held.

I don't understand how you get to this conclusion. biowait() will cause the
thread to sleep, and IPL_BIO interrupts will be accepted again while
it sleeps. Otherwise, all IPL_VM and lower interrupts would be blocked,
which would probably cause not only disklabel to hang, but most probably
the complete system.

I guess the problem is more that the USB I/O doesn't completes for some
reason.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--