[dm-devel] [PATCH 2/7] dm: Simplify dm_table_determine_type()

[Mike Snitzer]

On Wed, Nov 16 2016 at  4:53pm -0500,
Bart Van Assche <bart.vanassche at sandisk.com> wrote:

> On 11/16/2016 01:11 PM, Mike Snitzer wrote:
> >On Wed, Nov 16 2016 at  3:14pm -0500,
> >Bart Van Assche <bart.vanassche at sandisk.com> wrote:
> >>After having added WARN_ON_ONCE(sq_count == 0 && mq_count == 0)
> >>close to the end of dm_table_determine_type() the following output
> >>appeared:
> >>
> >>WARNING: CPU: 0 PID: 2458 at drivers/md/dm-table.c:966
> >>dm_table_complete+0x60e/0x6b0 [dm_mod]
> >>[ ... ]
> >>Call Trace:
> >> [<ffffffff81329b45>] dump_stack+0x68/0x93
> >> [<ffffffff810650e6>] __warn+0xc6/0xe0
> >> [<ffffffff810651b8>] warn_slowpath_null+0x18/0x20
> >> [<ffffffffa0021c8e>] dm_table_complete+0x60e/0x6b0 [dm_mod]
> >> [<ffffffffa00245cd>] table_load+0x13d/0x330 [dm_mod]
> >> [<ffffffffa0024490>] ? retrieve_status+0x1b0/0x1b0 [dm_mod]
> >> [<ffffffffa0025145>] ctl_ioctl+0x1f5/0x520 [dm_mod]
> >> [<ffffffffa002547e>] dm_ctl_ioctl+0xe/0x20 [dm_mod]
> >> [<ffffffff811f26cf>] do_vfs_ioctl+0x8f/0x6b0
> >> [<ffffffff811ff41c>] ? __fget+0x10c/0x200
> >> [<ffffffff811ff310>] ? expand_files+0x2a0/0x2a0
> >> [<ffffffff811f2d2c>] SyS_ioctl+0x3c/0x70
> >> [<ffffffff8163f9aa>] entry_SYSCALL_64_fastpath+0x18/0xad
> >>
> >>Is it intentional that dm_table_determine_type() can get called for
> >>a dm device with an empty table?
> >
> >What table were you trying to load when this occurred?
> >
> >Targets like the 'error' target don't have any devices.
> 
> Hello Mike,
> 
> This was the result of a table load issued by multipathd. Do you
> want me to add more debug code such that the details of the table
> load request are logged?

No, I think it's fine.  You likely have 'queue_if_no_path' configured
and multipathd is loading a 'multipath' table that doesn't have any
paths.