Re: 4.1-rc2 dm-multipath-mq kernel warning

[Mike Snitzer <snitzer@redhat.com>]

On Thu, May 28 2015 at 10:54am -0400,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> On 05/28/15 16:07, Mike Snitzer wrote:
> >On Thu, May 28 2015 at  9:10P -0400,
> >Mike Snitzer <snitzer@redhat.com> wrote:
> >
> >>On Thu, May 28 2015 at  4:19am -0400,
> >>Bart Van Assche <bart.vanassche@sandisk.com> wrote:
> >>
> >>>On 05/28/15 00:37, Mike Snitzer wrote:
> >>>>FYI, I've staged a variant patch for 4.1 that is simpler; along with the
> >>>>various fixes I've picked up from Junichi and the leak fix I emailed
> >>>>earlier.  They are now in linux-next and available in this 'dm-4.1'
> >>>>specific branch (based on 4.1-rc5):
> >>>>https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.1
> >>>>
> >>>>Please try and let me know if your test works.
> >>>
> >>>No data corruption was reported this time but a very large number of
> >>>memory leaks were reported by kmemleak. The initiator system ran out
> >>>of memory after some time due to these leaks. Here is an example of
> >>>a leak reported by kmemleak:
> >>>
> >>>unreferenced object 0xffff8800a39fc1a8 (size 96):
> >>>    comm "srp_daemon", pid 2116, jiffies 4294955508 (age 137.600s)
> >>>    hex dump (first 32 bytes):
> >>>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >>>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >>>    backtrace:
> >>>      [<ffffffff81600029>] kmemleak_alloc+0x49/0xb0
> >>>      [<ffffffff81167d19>] kmem_cache_alloc_node+0xd9/0x190
> >>>      [<ffffffff81425400>] scsi_init_request+0x20/0x40
> >>>      [<ffffffff812cbb98>] blk_mq_init_rq_map+0x228/0x290
> >>>      [<ffffffff812cbcc6>] blk_mq_alloc_tag_set+0xc6/0x220
> >>>      [<ffffffff81427488>] scsi_mq_setup_tags+0xc8/0xd0
> >>>      [<ffffffff8141e34f>] scsi_add_host_with_dma+0x6f/0x300
> >>>      [<ffffffffa04c62bf>] srp_create_target+0x11cf/0x1600 [ib_srp]
> >>>      [<ffffffff813f9c93>] dev_attr_store+0x13/0x20
> >>>      [<ffffffff81200a33>] sysfs_kf_write+0x43/0x60
> >>>      [<ffffffff811fff8b>] kernfs_fop_write+0x13b/0x1a0
> >>>      [<ffffffff81183e53>] __vfs_write+0x23/0xe0
> >>>      [<ffffffff81184524>] vfs_write+0xa4/0x1b0
> >>>      [<ffffffff811852d4>] SyS_write+0x44/0xb0
> >>>      [<ffffffff81613cdb>] system_call_fastpath+0x16/0x73
> >>>      [<ffffffffffffffff>] 0xffffffffffffffff
> >>
> >>I suspect I'm missing some cleanup of the request I got from the
> >>underlying blk-mq device.  I'll have a closer look.
> >
> >BTW, your test was with the dm-4.1 branch right?
> >
> >The above kmemleak trace clearly speaks to dm-mpath's ->clone_and_map_rq
> >having allocated the underlying scsi-mq request.  So it'll later require
> >a call to dm-mpath's ->release_clone_rq to free the associated memory --
> >which happens in dm.c:free_rq_clone().
> >
> >But I'm not yet seeing where we'd be missing a required call to
> >free_rq_clone() in the DM core error paths.  You can try this patch to
> >see if you hit the WARN_ON but I highly doubt you would.. similarly the
> >clone request shouldn't ever be allocated (nor tio->clone initialized)
> >in the REQUEUE case:
> 
> Hello Mike,
> 
> This occurred with the dm-4.1 branch merged with the for-4.2 IB
> branch. The leak was reported for regular I/O and before I started
> to trigger path failures. I had a look myself at how the
> sense_buffer pointer is manipulated by the scsi-mq code but could
> not find anything that is wrong. So the next I did was to repeat my
> test with kmemleak disabled. During this test the number of
> kmalloc-96 objects in /proc/slabinfo remained constant. So I
> probably have hit a bug in kmemleak. Maybe the code that clears and
> restores the sense buffer pointer in scsi_mq_prep_fn() is confusing
> kmemleak ? Sorry for the noise.

Ah, no problem, very good news (albeit strange)!

So you can confirm that with dm-4.1 your test passes?  If possible
please try your test a fews times.  Also, if time permits, please vary
scsi-mq and dm-mq enable/disable (4 permutations) to make sure all
supported modes pass your SRP torture test.

I just have to review Junichi's patch from today to silence the WARN_ON
I added; once I work through that I'll likely send dm-4.1 to Linus.

Thanks for all your help testing.
Mike