netdev - Re: DMA-API check_sync errors with 3.2

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Date:	Tue, 8 Nov 2011 13:16:17 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Dan Williams <dan.j.williams@...el.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...oraproject.org
Subject: Re: DMA-API check_sync errors with 3.2

On Tue, Nov 08, 2011 at 12:31:53PM -0500, Josh Boyer wrote:
> Hi All,
> 
> We have a few reports coming in on 3.2 git snapshots and 3.2-rc1
> where the DMA-API reports an error about a driver trying to sync
> memory it has not allocated.  I've seen a couple reports of this for
> sky2 and one for tg3, but I'm not sure if it's a driver problem or
> something a bit more generic.  An example trace is below:
> 
> backtrace:
> :WARNING: at lib/dma-debug.c:965 check_sync+0x2a8/0x530()
> :Hardware name: P5K-E
> :sky2 0000:02:00.0: DMA-API: device driver tries to sync DMA memory it has not
> allocated [device address=0x0000000105258040] [size=60 bytes]
> :Modules linked in: fuse lp parport ebtable_nat ebtables ipt_MASQUERADE
> iptable_nat nf_nat xt_CHECKSUM iptable_mangle tun bridge lockd stp llc
> ip6t_REJECT nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ipv6
> nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 ip6table_filter xt_state
> nf_conntrack ip6_tables raid1 uvcvideo videodev snd_usb_audio
> snd_hda_codec_hdmi media v4l2_compat_ioctl32 snd_usbmidi_lib joydev snd_rawmidi
> snd_seq_device snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_hwdep
> snd_pcm snd_timer snd microcode i2c_i801 iTCO_wdt iTCO_vendor_support serio_raw
> sky2 asus_atk0110 soundcore snd_page_alloc configfs virtio_net kvm_intel kvm
> uinput sunrpc raid10 btrfs zlib_deflate libcrc32c ata_generic pata_acpi
> firewire_ohci firewire_core crc_itu_t pata_jmicron radeon ttm drm_kms_helper
> drm i2c_algo_bit i2c_core [last unloaded: scsi_wait_scan]
> :Pid: 2520, comm: boinc Not tainted 3.2.0-0.rc0.git6.0.fc17.x86_64 #1
> :Call Trace:
> : <IRQ>  [<ffffffff8107ce9f>] warn_slowpath_common+0x7f/0xc0
> : [<ffffffff8107cf96>] warn_slowpath_fmt+0x46/0x50
> : [<ffffffff81325658>] check_sync+0x2a8/0x530
> : [<ffffffff81311c8e>] ? random32+0x2e/0x40
> : [<ffffffff81325b62>] debug_dma_sync_single_for_cpu+0x42/0x50
> : [<ffffffff81192cac>] ? ksize+0x1c/0xc0
> : [<ffffffff813217cc>] ? is_swiotlb_buffer+0x3c/0x50
> : [<ffffffff81321fe8>] ? swiotlb_sync_single+0x38/0x80
> : [<ffffffff8132212c>] ? swiotlb_sync_single_for_cpu+0xc/0x10
> : [<ffffffffa0331873>] sky2_poll+0x573/0xd90 [sky2]
> : [<ffffffff815454e1>] ? net_rx_action+0xa1/0x460
> : [<ffffffff815455a9>] net_rx_action+0x169/0x460
> : [<ffffffff81020c89>] ? sched_clock+0x9/0x10
> : [<ffffffff810ab9b5>] ? sched_clock_local+0x25/0x90
> : [<ffffffff810858f8>] __do_softirq+0xc8/0x3a0
> : [<ffffffff810ab9b5>] ? sched_clock_local+0x25/0x90
> : [<ffffffff81685efc>] call_softirq+0x1c/0x30
> : [<ffffffff8101b385>] do_softirq+0xa5/0xe0
> : [<ffffffff81085f2e>] irq_exit+0xbe/0xf0
> : [<ffffffff816867d3>] do_IRQ+0x63/0xe0
> : [<ffffffff8167b673>] common_interrupt+0x73/0x73
> : <EOI>  [<ffffffff8167b719>] ? retint_swapgs+0x13/0x1b
> 
> From what I can tell, net_rx_action is calling dma_issue_pending_all at
> the end of the function and this is forcing the flush and check (though
> I really haven't figured out why), and it's being attributed to the driver.
> 
> Originally there was a suggestion that c6a21d0b8d (dma-debug:
> hash_bucket_find needs to allow for offsets within an entry) would solve
> the issue, but that seems to have not proven true.  We still see this on
> kernels that have that commit included.  I've linked the bug reports below.
> 
> Any ideas?
> 
> josh
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=751005
> https://bugzilla.redhat.com/show_bug.cgi?id=751797
> https://bugzilla.redhat.com/show_bug.cgi?id=752113
> 
> 
The trace above looks to me like sky2_poll is calling receive_copy, which does
the pci_dma_sync_single_for_cpu, which resolves into the
swiotlb_sync_single_for_cpu call, and that triggers the warning.

Looking at the bugs, its hard to say exactly whats going on.  The sky2 case
looks like it should have easily found the hash bucket it needed (Juding by the
nice page aligned address for the dma rangs 0x0000000105258040), but the tg3
case looks like the dma address is just bogus (from bz 7451005, the device
address is 0x00000000d1668988, which doesn't look like anything a dma engine or
iotlb should return as a dma address.  It might mean that tg3 is breaking up
operations on its allocated dma ranges, which would cause this kind of warning,
but I cant' see where thats happening.

My first suggestion would be to, if you are able, instrument (via printk or
stap), get_hash_bucket and hash_bucket_find, so as to dump out the entire hash
table to the console when the failure occurs.  I know that will cause lots of
performance issues, but if this can be reproduced in a non-production
environment, it would let us at least see if we're just not finding the right
entry, or if the right entry doesn't exist.
Neil

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