Re: [PATCH v1 1/1] spi: Remove unneded check for orig_nents

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, May 22, 2024 at 03:18:18PM +0200, Neil Armstrong wrote:
> On 22/05/2024 13:53, Neil Armstrong wrote:
> > On 22/05/2024 13:33, Andy Shevchenko wrote:
> > > On Wed, May 22, 2024 at 12:03:33PM +0200, Neil Armstrong wrote:
> > > > On 15/05/2024 23:09, Nícolas F. R. A. Prado wrote:
> > > > > On Tue, May 07, 2024 at 11:10:27PM +0300, Andy Shevchenko wrote:
> > > > > > Both dma_unmap_sgtable() and sg_free_table() in spi_unmap_buf_attrs()
> > > > > > have checks for orig_nents against 0. No need to duplicate this.
> > > > > > All the same applies to other DMA mapping API calls.
> > > > > > 
> > > > > > Also note, there is no other user in the kernel that does this kind of
> > > > > > checks.
> > > > > > 
> > > > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > > > > 
> > > > > Hi,
> > > > > 
> > > > > this commit caused a regression which I reported here:
> > > > > 
> > > > > https://lore.kernel.org/all/d3679496-2e4e-4a7c-97ed-f193bd53af1d@notapiano
> > > > > 
> > > > > along with some thoughts on the cause and a possible solution, though I'm not
> > > > > familiar with this code base at all and would really appreciate any feedback you
> > > > > may have.
> > > > 
> > > > I also see the same regression on the SM8550 and SM8650 platforms,
> > > > please CC linux-arm-msm@xxxxxxxxxxxxxxx and me for a potential fix to test on those platforms.
> > > 
> > > There is still no answer from IOMMU patch author. Do you have the same trace
> > > due to IOMMU calls? Anyway, I guess it would be nice to see it.
> > 
> > Yes :
> > [    6.404623] Unable to handle kernel NULL pointer dereference at virtual address 000000000000001c
> > <snip>
> > [    6.641597] lr : __dma_sync_sg_for_device+0x3c/0x40
> > <snip>
> > [    6.688286] Call trace:
> > [    6.688287]  iommu_dma_sync_sg_for_device+0x28/0x100
> > [    6.717582]  __dma_sync_sg_for_device+0x3c/0x40
> > [    6.717585]  spi_transfer_one_message+0x358/0x680
> > [    6.732229]  __spi_pump_transfer_message+0x188/0x494
> > [    6.732232]  __spi_sync+0x2a8/0x3c4
> > [    6.732234]  spi_sync+0x30/0x54
> > [    6.732236]  goodix_berlin_spi_write+0xf8/0x164 [goodix_berlin_spi]
> > [    6.739854]  _regmap_raw_write_impl+0x538/0x674
> > [    6.750053]  _regmap_raw_write+0xb4/0x144
> > [    6.750056]  regmap_raw_write+0x7c/0xc0
> > [    6.750058]  goodix_berlin_power_on+0xb0/0x1b0 [goodix_berlin_core]
> > [    6.765520]  goodix_berlin_probe+0xc0/0x660 [goodix_berlin_core]
> > [    6.765522]  goodix_berlin_spi_probe+0x12c/0x14c [goodix_berlin_spi]
> > [    6.772339]  spi_probe+0x84/0xe4
> > [    6.772342]  really_probe+0xbc/0x29c
> > [    6.784313]  __driver_probe_device+0x78/0x12c
> > [    6.784316]  driver_probe_device+0x3c/0x15c
> > [    6.784319]  __driver_attach+0x90/0x19c
> > [    6.784322]  bus_for_each_dev+0x7c/0xdc
> > [    6.794520]  driver_attach+0x24/0x30
> > [    6.794523]  bus_add_driver+0xe4/0x208
> > [    6.794526]  driver_register+0x5c/0x124
> > [    6.802586]  __spi_register_driver+0xa4/0xe4
> > [    6.802589]  goodix_berlin_spi_driver_init+0x20/0x1000 [goodix_berlin_spi]
> > [    6.802591]  do_one_initcall+0x80/0x1c8
> > [    6.902310]  do_init_module+0x60/0x218
> > [    6.921988]  load_module+0x1bcc/0x1d8c
> > [    6.925847]  init_module_from_file+0x88/0xcc
> > [    6.930238]  __arm64_sys_finit_module+0x1dc/0x2e4
> > [    6.935074]  invoke_syscall+0x48/0x114
> > [    6.938944]  el0_svc_common.constprop.0+0xc0/0xe0
> > [    6.943781]  do_el0_svc+0x1c/0x28
> > [    6.947195]  el0_svc+0x34/0xd8
> > [    6.950348]  el0t_64_sync_handler+0x120/0x12c
> > [    6.954833]  el0t_64_sync+0x190/0x194
> > [    6.958600] Code: 2a0203f5 2a0303f6 a90363f7 aa0003f7 (b9401c2
> > 
> > Reverting  8cc3bad9d9d6 ("spi: Remove unneded check for orig_nents") removes the crash.
> > 
> > > 
> > > Meanwhile, I have three changes I posted in the replies to the initial report,
> > > can you combine them all and test? This will be a plan B (? or A, depending on
> > > the culprit).
> > > 
> > 
> > I'll try to apply them and test.
> 
> I stacked the 3 changes, and it works:
> Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx> # on SM8650-QRD

Thank you!

I will try to develop and submit a fix against IOMMU which I believe is the
correct place to address this. So, this one will be plan B in case the IOMMU
folks will refuse the other one.

-- 
With Best Regards,
Andy Shevchenko