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Date: Thu, 10 Sep 2020 12:22:31 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Rob Herring <robh@...nel.org>,
Xingxing Su <suxingxing@...ngson.cn>,
Bjorn Helgaas <bhelgaas@...gle.com>,
PCI <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>,
Scott Branden <scott.branden@...adcom.com>
Subject: Re: [PATCH] PCI: Don't use Printk in raw_spinlocks
On 9/10/2020 12:20 PM, Bjorn Helgaas wrote:
> On Thu, Sep 10, 2020 at 11:50:07AM -0700, Florian Fainelli wrote:
>> On 9/10/2020 11:46 AM, Bjorn Helgaas wrote:
>>> On Thu, Sep 10, 2020 at 08:21:06AM -0600, Rob Herring wrote:
>>>> On Wed, Sep 9, 2020 at 8:07 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>>
>>>>> [+cc Mark, Florian, Rob, Scott]
>>>>>
>>>>> On Sat, Aug 01, 2020 at 09:25:49AM +0800, Xingxing Su wrote:
>>>>>> Do not use printk in raw_spinlocks,
>>>>>> it will cause BUG: Invalid wait context.
>>>>>>
>>>>>> The trace reported by lockdep follows.
>>>>>>
>>>>>> [ 2.986113] =============================
>>>>>> [ 2.986115] [ BUG: Invalid wait context ]
>>>>>> [ 2.986116] 5.8.0-rc1+ #11 Not tainted
>>>>>> [ 2.986118] -----------------------------
>>>>>> [ 2.986120] swapper/0/1 is trying to lock:
>>>>>> [ 2.986122] ffffffff80f5ddd8 (console_owner){....}-{3:3}, at: console_unlock+0x284/0x820
>>>>>> [ 2.986130] other info that might help us debug this:
>>>>>> [ 2.986132] context-{5:5}
>>>>>> [ 2.986134] 3 locks held by swapper/0/1:
>>>>>> [ 2.986135] #0: 98000007fa03c990 (&dev->mutex){....}-{0:0}, at: device_driver_attach+0x28/0x90
>>>>>> [ 2.986144] #1: ffffffff80fb83a8 (pci_lock){....}-{2:2}, at: pci_bus_write_config_word+0x60/0xb8
>>>>>> [ 2.986152] #2: ffffffff80f5ded0 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0x1b0/0x3b8
>>>>>> [ 2.986161] stack backtrace:
>>>>>> [ 2.986163] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc1+ #11
>>>>>> [ 2.986164] Stack : 0000000000001d67 98000000030be9b0 0000000000000001 7b2aba74f6c4785b
>>>>>> [ 2.986172] 7b2aba74f6c4785b 0000000000000000 98000007f89cb438 ffffffff80e7dc80
>>>>>> [ 2.986181] 0000000000000001 000000000000000a 0000000000000001 0000000000000001
>>>>>> [ 2.986189] ffffffff80f4e156 fffffffffffffffd ffffffff80cc2d98 fffffffff8000000
>>>>>> [ 2.986197] 0000000024000000 ffffffff80f40000 0000000000000000 0000000000000000
>>>>>> [ 2.986205] ffffffff9500cce0 0000000000000000 ffffffff80f50000 ffffffff81546318
>>>>>> [ 2.986213] ffffffff81c4c3c0 0000000000000018 ffffffffbc000000 0000000000000000
>>>>>> [ 2.986221] ffffffff81340000 98000007f89c8000 98000007f89cb430 98000007f8a00000
>>>>>> [ 2.986229] ffffffff806be568 0000000000000000 0000000000000000 0000000000000000
>>>>>> [ 2.986237] 0000000000000000 0000000000000000 ffffffff80211c1c 7b2aba74f6c4785b
>>>>>> [ 2.986245] ...
>>>>>> [ 2.986250] Call Trace:
>>>>>> [ 2.986251] [<ffffffff80211c1c>] show_stack+0x9c/0x130
>>>>>> [ 2.986253] [<ffffffff806be568>] dump_stack+0xe8/0x150
>>>>>> [ 2.986255] [<ffffffff802ad408>] __lock_acquire+0x570/0x3250
>>>>>> [ 2.986257] [<ffffffff802abed0>] lock_acquire+0x118/0x558
>>>>>> [ 2.986259] [<ffffffff802be764>] console_unlock+0x2e4/0x820
>>>>>> [ 2.986261] [<ffffffff802c0a68>] vprintk_emit+0x1c0/0x3b8
>>>>>> [ 2.986263] [<ffffffff807f45a8>] dev_vprintk_emit+0x1c8/0x210
>>>>>> [ 2.986265] [<ffffffff807f462c>] dev_printk_emit+0x3c/0x60
>>>>>> [ 2.986267] [<ffffffff807f499c>] _dev_warn+0x5c/0x80
>>>>>> [ 2.986269] [<ffffffff806eea9c>] pci_generic_config_write32+0x154/0x160
>>>>>> [ 2.986271] [<ffffffff806edca4>] pci_bus_write_config_word+0x84/0xb8
>>>>>> [ 2.986273] [<ffffffff806f1664>] pci_setup_device+0x22c/0x768
>>>>>> [ 2.986275] [<ffffffff806f26a0>] pci_scan_single_device+0xc8/0x100
>>>>>> [ 2.986277] [<ffffffff806f2788>] pci_scan_slot+0xb0/0x178
>>>>>> [ 2.986279] [<ffffffff806f3ae4>] pci_scan_child_bus_extend+0x5c/0x370
>>>>>> [ 2.986281] [<ffffffff806f407c>] pci_scan_root_bus_bridge+0x6c/0xf0
>>>>>> [ 2.986283] [<ffffffff806f411c>] pci_host_probe+0x1c/0xd8
>>>>>> [ 2.986285] [<ffffffff807fa03c>] platform_drv_probe+0x54/0xb8
>>>>>> [ 2.986287] [<ffffffff807f71f8>] really_probe+0x130/0x388
>>>>>> [ 2.986289] [<ffffffff807f7594>] driver_probe_device+0x64/0xd8
>>>>>> [ 2.986291] [<ffffffff807f7844>] device_driver_attach+0x84/0x90
>>>>>> [ 2.986293] [<ffffffff807f7918>] __driver_attach+0xc8/0x128
>>>>>> [ 2.986295] [<ffffffff807f4cac>] bus_for_each_dev+0x74/0xd8
>>>>>> [ 2.986297] [<ffffffff807f6408>] bus_add_driver+0x170/0x250
>>>>>> [ 2.986299] [<ffffffff807f899c>] driver_register+0x84/0x150
>>>>>> [ 2.986301] [<ffffffff80200b08>] do_one_initcall+0x98/0x458
>>>>>> [ 2.986303] [<ffffffff810212dc>] kernel_init_freeable+0x2c0/0x36c
>>>>>> [ 2.986305] [<ffffffff80be7540>] kernel_init+0x10/0x128
>>>>>> [ 2.986307] [<ffffffff80209d44>] ret_from_kernel_thread+0x14/0x1c
>>>>>>
>>>>>> Signed-off-by: Xingxing Su <suxingxing@...ngson.cn>
>>>>>> ---
>>>>>> drivers/pci/access.c | 3 ---
>>>>>> 1 file changed, 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
>>>>>> index 79c4a2e..b3fc164 100644
>>>>>> --- a/drivers/pci/access.c
>>>>>> +++ b/drivers/pci/access.c
>>>>>> @@ -160,9 +160,6 @@ int pci_generic_config_write32(struct pci_bus *bus, unsigned int devfn,
>>>>>> * write happen to have any RW1C (write-one-to-clear) bits set, we
>>>>>> * just inadvertently cleared something we shouldn't have.
>>>>>> */
>>>>>> - dev_warn_ratelimited(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
>>>>>> - size, pci_domain_nr(bus), bus->number,
>>>>>> - PCI_SLOT(devfn), PCI_FUNC(devfn), where);
>>>>>
>>>>> We just changed this printk (see [1]), but I think we still have this
>>>>> lockdep problem even after Mark's change. So I guess we need another
>>>>> think about this.
>>>>>
>>>>> Maybe we can print something when registering pci_ops that use
>>>>> pci_generic_config_write32()?
>>>>
>>>> That was my suggestion, but as Mark pointed out that doesn't work if
>>>> pci_generic_config_write32 is wrapped (which is 4 out of 8 cases).
>>>>
>>>> Also, 3 of the cases are only for the root bus (bridge). Are 32-bit
>>>> writes to a bridge going to cause problems? For xgene, interestingly,
>>>> with DT _write32 is needed, but for ACPI it is not (only _read32). I
>>>> think xgene is practically dead though a few people still have
>>>> systems, but likely xgene with DT is really dead. The ECAM case was
>>>> for QCom server which is also pretty much dead. SA1100 nano-engine is
>>>> really old and something only a few people have at most (Russell
>>>> King). So ignoring all those, we're left with just loongson and iproc.
>>>> Maybe just remove the warning?
>>>
>>> Sigh, removing it sounds like the best option.
>>
>> Given that we have to go by a list of drivers, how about we add another
>> pci_bus_flags_t flag to indicate 32-bit configuration space accessors are
>> used and key off that bit to issue the warning?
>
> I think that's basically what Mark's patch does: https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?h=pci/enumeration&id=92ff4b49c2a9
Yes indeed, not enough coffee, clearly.
>
> But of course we still have to deal with the lockdep problem.
>
--
Florian
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