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Date: Mon, 14 Oct 2013 14:30:34 +0200
From: Jan Kara <jack@suse.cz>
To: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        Hans de Goede <hdegoede@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: Warning when calling radix_tree_insert on 3.12-rc4
Message-ID: <20131014123034.GF19604@quack.suse.cz>
References: <20131011221315.GE7094@xanatos>
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  Hello Sarah,

On Fri 11-10-13 15:13:15, Sarah Sharp wrote:
> I'm testing out some changes to the xHCI USB host controller driver
> (which uses a radix tree when a UAS device is attached to the host), and
> I noticed the following warning:
> 
> Oct 11 14:42:08 xanatos kernel: [18165.819014] usb 2-2: new SuperSpeed USB device number 2 using xhci_hcd
> Oct 11 14:42:08 xanatos kernel: [18165.836264] usb 2-2: New USB device found, idVendor=174c, idProduct=55aa
> Oct 11 14:42:08 xanatos kernel: [18165.836271] usb 2-2: New USB device strings: Mfr=2, Product=3, SerialNumber=1
> Oct 11 14:42:08 xanatos kernel: [18165.836275] usb 2-2: Product: Plugable USB3-SATA-UASP1
> Oct 11 14:42:08 xanatos kernel: [18165.836279] usb 2-2: Manufacturer: ASM1053E
> Oct 11 14:42:08 xanatos kernel: [18165.836291] usb 2-2: SerialNumber: 123456789045
> Oct 11 14:42:08 xanatos kernel: [18165.847661] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/8759
> Oct 11 14:42:08 xanatos kernel: [18165.847667] caller is radix_tree_node_alloc+0x5c/0xa0
  Well, this warning seems to come from the __get_cpu_var() function. I don't
see how my commit could have caused what you observe. It seems you are
calling radix_tree_insert() for a radix tree which has atomic gfp mask set
and you don't do radix_tree_preload() / radix_tree_preload_end() around
that? That was always problematic and could lead to the above warning.

I'm not sure in which contexts xhci_update_stream_ring() can be called. But
if you are guaranteed non-atomic context, then using radix_tree_preload()
with a more relaxed gfp mask is good (lowers pressure on atomic allocations).

If the context depends on the caller, things are more complex. Generally,
you can use radix_tree_maybe_preload() but you have to set gfp mask
argument according to the context. The function then figures out whether
it's worth it to do a preload or not (but it always does preempt_disable()
which will silence the warning).

									Honza

> Oct 11 14:42:08 xanatos kernel: [18165.847670] CPU: 1 PID: 8759 Comm: modprobe Not tainted 3.12.0-rc4+ #94
> Oct 11 14:42:08 xanatos kernel: [18165.847671] Hardware name: LENOVO 2325AP7/2325AP7, BIOS G2ET82WW (2.02 ) 09/11/2012
> Oct 11 14:42:08 xanatos kernel: [18165.847673]  ffff88010c1d3fd8 ffff88010c1d38e8 ffffffff816081b9 0000000000000007
> Oct 11 14:42:08 xanatos kernel: [18165.847677]  0000000000000001 ffff88010c1d3918 ffffffff812e3ffc ffff88010c26c988
> Oct 11 14:42:08 xanatos kernel: [18165.847679]  0000000000000020 00000000000240b1 0000000000000003 ffff88010c1d3938
> Oct 11 14:42:08 xanatos kernel: [18165.847682] Call Trace:
> Oct 11 14:42:08 xanatos kernel: [18165.847686]  [<ffffffff816081b9>] dump_stack+0x4f/0x84
> Oct 11 14:42:08 xanatos kernel: [18165.847689]  [<ffffffff812e3ffc>] debug_smp_processor_id+0xdc/0x100
> Oct 11 14:42:08 xanatos kernel: [18165.847692]  [<ffffffff812d47fc>] radix_tree_node_alloc+0x5c/0xa0
> Oct 11 14:42:08 xanatos kernel: [18165.847695]  [<ffffffff812d48d5>] radix_tree_insert+0x95/0x260
> Oct 11 14:42:08 xanatos kernel: [18165.847702]  [<ffffffffa008446f>] xhci_update_stream_ring+0x8f/0xc0 [xhci_hcd]
> Oct 11 14:42:08 xanatos kernel: [18165.847708]  [<ffffffffa00860f0>] xhci_alloc_stream_info+0x190/0x410 [xhci_hcd]
> Oct 11 14:42:08 xanatos kernel: [18165.847713]  [<ffffffffa00802ef>] xhci_alloc_streams+0x36f/0x750 [xhci_hcd]
> Oct 11 14:42:08 xanatos kernel: [18165.847716]  [<ffffffff8108678f>] ? ttwu_stat+0xef/0x160
> Oct 11 14:42:08 xanatos kernel: [18165.847720]  [<ffffffff810c8e93>] ? is_module_address+0x33/0x60
> Oct 11 14:42:08 xanatos kernel: [18165.847729]  [<ffffffffa0036e35>] usb_alloc_streams+0x95/0xb0 [usbcore]
> Oct 11 14:42:08 xanatos kernel: [18165.847732]  [<ffffffffa01eb874>] uas_configure_endpoints+0x154/0x210 [uas]
> Oct 11 14:42:08 xanatos kernel: [18165.847735]  [<ffffffffa01ec367>] uas_probe+0x2d7/0x390 [uas]
> Oct 11 14:42:08 xanatos kernel: [18165.847743]  [<ffffffffa0040053>] usb_probe_interface+0x1c3/0x2f0 [usbcore]
> Oct 11 14:42:08 xanatos kernel: [18165.847746]  [<ffffffff813ba421>] driver_probe_device+0x91/0x3c0
> Oct 11 14:42:08 xanatos kernel: [18165.847749]  [<ffffffff813ba7fb>] __driver_attach+0xab/0xb0
> Oct 11 14:42:08 xanatos kernel: [18165.847751]  [<ffffffff813ba750>] ? driver_probe_device+0x3c0/0x3c0
> Oct 11 14:42:08 xanatos kernel: [18165.847753]  [<ffffffff813b835e>] bus_for_each_dev+0x5e/0x90
> Oct 11 14:42:08 xanatos kernel: [18165.847756]  [<ffffffff813b9e6e>] driver_attach+0x1e/0x20
> Oct 11 14:42:08 xanatos kernel: [18165.847758]  [<ffffffff813b988f>] bus_add_driver+0x10f/0x2d0
> Oct 11 14:42:08 xanatos kernel: [18165.847760]  [<ffffffff813baf24>] driver_register+0x64/0xf0
> Oct 11 14:42:08 xanatos kernel: [18165.847767]  [<ffffffffa003ec34>] usb_register_driver+0xc4/0x180 [usbcore]
> Oct 11 14:42:08 xanatos kernel: [18165.847770]  [<ffffffffa01f0000>] ? 0xffffffffa01effff
> Oct 11 14:42:08 xanatos kernel: [18165.847773]  [<ffffffffa01f001e>] uas_driver_init+0x1e/0x20 [uas]
> Oct 11 14:42:08 xanatos kernel: [18165.847775]  [<ffffffff8100210a>] do_one_initcall+0xda/0x180
> Oct 11 14:42:08 xanatos kernel: [18165.847778]  [<ffffffff81080313>] ? __blocking_notifier_call_chain+0x63/0x80
> Oct 11 14:42:08 xanatos kernel: [18165.847782]  [<ffffffff810c7e42>] load_module+0x14b2/0x1ad0
> Oct 11 14:42:08 xanatos kernel: [18165.847784]  [<ffffffff810c4680>] ? show_initstate+0x50/0x50
> Oct 11 14:42:08 xanatos kernel: [18165.847788]  [<ffffffff810c8532>] SyS_init_module+0xd2/0x120
> Oct 11 14:42:08 xanatos kernel: [18165.847791]  [<ffffffff816183a9>] system_call_fastpath+0x16/0x1b
> 
> This looks possibly related to commit
> 5e4c0d974139a98741b829b27cf38dc8f9284490 "lib/radix-tree.c: make
> radix_tree_node_alloc() work correctly within interrupt".  I'll revert
> the commit, and see if the warning disappears.  In the meantime, can you
> look into fixing this?
> 
> Thanks,
> Sarah Sharp
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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