linux-kernel - Re: [PATCH -next v2] usb: xhci: do not free an empty cmd ring

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Message-Id: <eff504ed-d5b0-171a-8eb8-f073f2ee9271@kylinos.cn>
Date:   Thu, 30 Mar 2023 10:58:57 +0800
From:   Hongyu Xie <xiehongyu1@...inos.cn>
To:     mathias.nyman@...ux.intel.com, mathias.nyman@...el.com,
        gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, sunke <sunke@...inos.cn>,
        Hongyu Xie <xiehongyu1@...inos.cn>
Subject: Re: [PATCH -next v2] usb: xhci: do not free an empty cmd ring

Hi,

在 2023/3/27 22:58, Mathias Nyman 写道:
> On 27.3.2023 4.11, Hongyu Xie wrote:
>> It was first found on HUAWEI Kirin 9006C platform with a builtin xhci
>> controller during stress cycle test(stress-ng, glmark2, x11perf, S4...).
>>
>> phase one:
>> [26788.706878] PM: dpm_run_callback(): platform_pm_thaw+0x0/0x68 returns -12
>> [26788.706878] PM: Device xhci-hcd.1.auto failed to thaw async: error -12
>> ...
>> phase two:
>> [28650.583496] [2023:01:19 04:43:29]Unable to handle kernel NULL pointer dereference at virtual address 0000000000000028
>> ...
>> [28650.583526] user pgtable: 4k pages, 39-bit VAs, pgdp=000000027862a000
>> [28650.583557] [0000000000000028] pgd=0000000000000000
>> ...
>> [28650.583587] pc : xhci_suspend+0x154/0x5b0
>> [28650.583618] lr : xhci_suspend+0x148/0x5b0
>> [28650.583618] sp : ffffffc01c7ebbd0
>> [28650.583618] x29: ffffffc01c7ebbd0 x28: ffffffec834d0000
>> [28650.583618] x27: ffffffc0106a3cc8 x26: ffffffb2c540c848
>> [28650.583618] x25: 0000000000000000 x24: ffffffec82ee30b0
>> [28650.583618] x23: ffffffb43b31c2f8 x22: 0000000000000000
>> [28650.583618] x21: 0000000000000000 x20: ffffffb43b31c000
>> [28650.583648] x19: ffffffb43b31c2a8 x18: 0000000000000001
>> [28650.583648] x17: 0000000000000803 x16: 00000000fffffffe
>> [28650.583648] x15: 0000000000001000 x14: ffffffb150b67e00
>> [28650.583648] x13: 00000000f0000000 x12: 0000000000000001
>> [28650.583648] x11: 0000000000000000 x10: 0000000000000a80
>> [28650.583648] x9 : ffffffc01c7eba00 x8 : ffffffb43ad10ae0
>> [28650.583648] x7 : ffffffb84cd98dc0 x6 : 0000000cceb6a101
>> [28650.583679] x5 : 00ffffffffffffff x4 : 0000000000000001
>> [28650.583679] x3 : 0000000000000011 x2 : 0000000000e2cfa8
>> [28650.583679] x1 : 00000000823535e1 x0 : 0000000000000000
>>
>> gdb:
>> (gdb) l *(xhci_suspend+0x154)
>> 0xffffffc010b6cd44 is in xhci_suspend (/.../drivers/usb/host/xhci.c:854).
>> 849	{
>> 850		struct xhci_ring *ring;
>> 851		struct xhci_segment *seg;
>> 852
>> 853		ring = xhci->cmd_ring;
>> 854		seg = ring->deq_seg;
>> (gdb) disassemble 0xffffffc010b6cd44
>> ...
>> 0xffffffc010b6cd40 <+336>:	ldr	x22, [x19, #160]
>> 0xffffffc010b6cd44 <+340>:	ldr	x20, [x22, #40]
>> 0xffffffc010b6cd48 <+344>:	mov	w1, #0x0                   	// #0
>>
>> During phase one, platform_pm_thaw called xhci_plat_resume which called
>> xhci_resume. The rest possible calling routine might be
>> xhci_resume->xhci_init->xhci_mem_init, and xhci->cmd_ring was cleaned in
>> xhci_mem_cleanup before xhci_mem_init returned -ENOMEM.
>>
>> During phase two, systemd was tring to hibernate again and called
>> xhci_suspend, then xhci_clear_command_ring dereferenced xhci->cmd_ring
>> which was already NULL.
>>
> 
> Any comments on the questions I had on the first version of the patch?
Sorry, didn't notice your reply in the first version.
> 
> xhci_mem_init() failing with -ENOMEM looks like the real problem here.
> 
> Are we really running out of memory? does kmemleak say anything?
It looks like running out of memory, since it was running a stress test. 
But can't go any further without more details. Didn't run with kmemleak 
open.
> Any chance you could look into where exactly xhci_mem_init() fails as
> xhci_mem_init() always returns -ENOMEM on failure?
Can't reproduce the problem for a very long time. Still don't know where 
did it fail in xhci_mem_init. But I think you can't blame xhci driver 
for memory shortage, and you can't fix that.
> 
>> So if xhci->cmd_ring is NULL, xhci_clear_command_ring just return.
> 
> This hides the problem more than solves it. Root cause is still unknown
You were saying "If xhci_mem_init() failed then...it shouldn't be...", 
and I agree with it. Further more, I think functions that calling 
xhci_mem_init needs to check xhci_mem_init's return value, but it needs 
another patch to do this. This patch is saying that 
xhci_clear_command_ring should check a pointer before using it, because 
somewhere else might clear cmd_ring, that's all.
> 
> Thanks
> Mathias
> 
> 
Thanks

Hongyu Xie