Re: [PATCH rdma-next v1 1/2] lib/scatterlist: Fix wrong update of orig_nents

[Leon Romanovsky <leon@kernel.org>]

On Wed, Jun 30, 2021 at 07:44:21PM +0200, Thierry Reding wrote:
> On Wed, Jun 30, 2021 at 01:12:26PM +0200, Marek Szyprowski wrote:
> > Hi Leon,
> > 
> > On 29.06.2021 10:40, Leon Romanovsky wrote:
> > > From: Maor Gottlieb <maorg@nvidia.com>
> > >
> > > orig_nents should represent the number of entries with pages,
> > > but __sg_alloc_table_from_pages sets orig_nents as the number of
> > > total entries in the table. This is wrong when the API is used for
> > > dynamic allocation where not all the table entries are mapped with
> > > pages. It wasn't observed until now, since RDMA umem who uses this
> > > API in the dynamic form doesn't use orig_nents implicit or explicit
> > > by the scatterlist APIs.
> > >
> > > Fix it by:
> > > 1. Set orig_nents as number of entries with pages also in
> > >     __sg_alloc_table_from_pages.
> > > 2. Add a new field total_nents to reflect the total number of entries
> > >     in the table. This is required for the release flow (sg_free_table).
> > >     This filed should be used internally only by scatterlist.
> > >
> > > Fixes: 07da1223ec93 ("lib/scatterlist: Add support in dynamic allocation of SG table from pages")
> > > Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
> > > Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> > 
> > This patch landed in linux-next 20210630 as commit a52724456928 
> > ("lib/scatterlist: Fix wrong update of orig_nents"). It causes serious 
> > regression in DMA-IOMMU integration, which can be observed for example 
> > on ARM Juno board during boot:
> > 
> > Unable to handle kernel paging request at virtual address 00376f42a6e40454
> > Mem abort info:
> >    ESR = 0x96000004
> >    EC = 0x25: DABT (current EL), IL = 32 bits
> >    SET = 0, FnV = 0
> >    EA = 0, S1PTW = 0
> >    FSC = 0x04: level 0 translation fault
> > Data abort info:
> >    ISV = 0, ISS = 0x00000004
> >    CM = 0, WnR = 0
> > [00376f42a6e40454] address between user and kernel address ranges
> > Internal error: Oops: 96000004 [#1] PREEMPT SMP
> > Modules linked in:
> > CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.13.0-next-20210630+ #3585
> > Hardware name: ARM Juno development board (r1) (DT)
> > pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
> > pc : __sg_free_table+0x60/0xa0
> > lr : __sg_free_table+0x7c/0xa0
> > ..
> > Call trace:
> >   __sg_free_table+0x60/0xa0
> >   sg_free_table+0x1c/0x28
> >   iommu_dma_alloc+0xc8/0x388
> >   dma_alloc_attrs+0xcc/0xf0
> >   dmam_alloc_attrs+0x68/0xb8
> >   sil24_port_start+0x60/0xe0
> >   ata_host_start.part.32+0xbc/0x208
> >   ata_host_activate+0x64/0x150
> >   sil24_init_one+0x1e8/0x268
> >   local_pci_probe+0x3c/0xa0
> >   pci_device_probe+0x128/0x1c8
> >   really_probe+0x138/0x2d0
> >   __driver_probe_device+0x78/0xd8
> >   driver_probe_device+0x40/0x110
> >   __driver_attach+0xcc/0x118
> >   bus_for_each_dev+0x68/0xc8
> >   driver_attach+0x20/0x28
> >   bus_add_driver+0x168/0x1f8
> >   driver_register+0x60/0x110
> >   __pci_register_driver+0x5c/0x68
> >   sil24_pci_driver_init+0x20/0x28
> >   do_one_initcall+0x84/0x450
> >   kernel_init_freeable+0x31c/0x38c
> >   kernel_init+0x20/0x120
> >   ret_from_fork+0x10/0x18
> > Code: d37be885 6b01007f 52800004 540000a2 (f8656813)
> > ---[ end trace 4ba4f0c9c48711a1 ]---
> > Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> > 
> > It looks that some changes to the scatterlist structures are missing 
> > outside of the lib/scatterlist.c.
> > 
> > For now I would suggest to revert this change.
> 
> I see a very similar crash on Tegra during the HDA driver's probe.
> 
> Leon, let me know if you need a tester for a replacement patch.

With a great pleasure, I'll contact you offline when we prepare it.

For now, this patch will be dropped.

Thanks

> 
> Thanks,
> Thierry