Re: [PATCH] usb: gadget: f_fs: data_len used before properly set

[John Stultz]

On Wed, Jun 12, 2019 at 3:13 PM <fei.yang@xxxxxxxxx> wrote:
>
> From: Fei Yang <fei.yang@xxxxxxxxx>
>
> The following line of code in function ffs_epfile_io is trying to set
> flag io_data->use_sg in case buffer required is larger than one page.
>
>     io_data->use_sg = gadget->sg_supported && data_len > PAGE_SIZE;
>
> However at this point of time the variable data_len has not been set
> to the proper buffer size yet. The consequence is that io_data->use_sg
> is always set regardless what buffer size really is, because the condition
> (data_len > PAGE_SIZE) is effectively an unsigned comparison between
> -EINVAL and PAGE_SIZE which would always result in TRUE.
>
> Fixes: 772a7a724f69 ("usb: gadget: f_fs: Allow scatter-gather buffers")
> Signed-off-by: Fei Yang <fei.yang@xxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx>

Hey Fei! Thanks so much for sending this out! I was excited that this
might resolve the ffs stalls I've been seeing on dwc3/dwc2 hardware,
but when I gave it a shot, it doesn't seem to help. In fact, rather
then a stall, I end up seeing the following panic:

[  383.415362] Unable to handle kernel read from unreadable memory at
virtual address 0000000000000018
[  383.431935] Mem abort info:
[  383.431937]   ESR = 0x96000005
[  383.431940]   Exception class = DABT (current EL), IL = 32 bits
[  383.431941]   SET = 0, FnV = 0
[  383.431942]   EA = 0, S1PTW = 0
[  383.431943] Data abort info:
[  383.431945]   ISV = 0, ISS = 0x00000005
[  383.431946]   CM = 0, WnR = 0
[  383.431951] user pgtable: 4k pages, 39-bit VAs, pgdp=00000000aae1f000
[  383.431953] [0000000000000018] pgd=000000009f064003,
pud=000000009f064003, pmd=0000000000000000
[  383.482560] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[  383.488128] Modules linked in:
[  383.491181] CPU: 0 PID: 399 Comm: irq/69-dwc3 Tainted: G S
      5.2.0-rc4-00092-gf5f12f5d3fdd #296
[  383.501002] Hardware name: HiKey960 (DT)
[  383.504918] pstate: 20400085 (nzCv daIf +PAN -UAO)
[  383.509714] pc : dma_direct_unmap_sg+0x38/0x80
[  383.514151] lr : dma_direct_unmap_sg+0x5c/0x80
[  383.518586] sp : ffffff8011fcbc40
[  383.521893] x29: ffffff8011fcbc40 x28: ffffffc0bad9c180
[  383.527199] x27: ffffffc0bae05300 x26: 0000000000000002
[  383.532504] x25: ffffffc0b9a9fd00 x24: 0000000000000000
[  383.537809] x23: 0000000000000001 x22: ffffffc0bad9fc10
[  383.543114] x21: 0000000000000002 x20: 0000000000000001
[  383.548420] x19: 0000000000000000 x18: 0000000000000000
[  383.553726] x17: 0000000000000000 x16: 0000000000000000
[  383.559032] x15: 0000000000000000 x14: ffffff8010eb6ad0
[  383.564338] x13: 0000000000000000 x12: 0000000000000000
[  383.569643] x11: 0000000000000000 x10: 00000000000009d0
[  383.574949] x9 : ffffff8011fcbd20 x8 : ffffffc0b63c3a30
[  383.580254] x7 : ffffffc0bc515c00 x6 : 0000000000000007
[  383.585560] x5 : 0000000000000001 x4 : 0000000000000004
[  383.590865] x3 : 0000000000000001 x2 : 0000000000000001
[  383.596169] x1 : 000000000006bf42 x0 : 0000000000000000
[  383.601477] Call trace:
[  383.603916]  dma_direct_unmap_sg+0x38/0x80
[  383.608013]  usb_gadget_unmap_request_by_dev+0xb0/0xc8
[  383.613148]  dwc3_gadget_del_and_unmap_request.isra.13+0x78/0x150
[  383.619235]  dwc3_gadget_giveback+0x30/0x68
[  383.623412]  dwc3_thread_interrupt+0x694/0x14e0
[  383.627938]  irq_thread_fn+0x28/0x78
[  383.631506]  irq_thread+0x124/0x1c0
[  383.634991]  kthread+0x128/0x130
[  383.638214]  ret_from_fork+0x10/0x1c
[  383.641786] Code: 2a0303f7 aa0403f8 52800014 d503201f (b9401a62)
[  383.647874] ---[ end trace f48053c2040c5658 ]---

>From the looks of it though, I suspect your fix is a good one, and
maybe its just helping expose some related underlying issues in the
dwc3 driver?

thanks
-john