Re: [PATCH v2] powerpc/iommu: Fix the iommu group reference leak during platform domain attach

[Jason Gunthorpe]

On Wed, Feb 14, 2024 at 12:09:24PM -0600, Shivaprasad G Bhat wrote:
> The function spapr_tce_platform_iommu_attach_dev() is missing to call
> iommu_group_put() when the domain is already set. This refcount leak
> shows up with BUG_ON() during DLPAR remove operation as,
> 
>   KernelBug: Kernel bug in state 'None': kernel BUG at arch/powerpc/platforms/pseries/iommu.c:100!
>   Oops: Exception in kernel mode, sig: 5 [#1]
>   LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=8192 NUMA pSeries
>   <snip>
>   Hardware name: IBM,9080-HEX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1060.00 (NH1060_016) hv:phyp pSeries
>   NIP:  c0000000000ff4d4 LR: c0000000000ff4cc CTR: 0000000000000000
>   REGS: c0000013aed5f840 TRAP: 0700   Tainted: G          I         (6.8.0-rc3-autotest-g99bd3cb0d12e)
>   MSR:  8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 44002402  XER: 20040000
>   CFAR: c000000000a0d170 IRQMASK: 0
>   GPR00: c0000000000ff4cc c0000013aed5fae0 c000000001512700 c0000013aa362138
>   GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000119c8afd0
>   GPR08: 0000000000000000 c000001284442b00 0000000000000001 0000000000001003
>   GPR12: 0000000300000000 c0000018ffff2f00 0000000000000000 0000000000000000
>   GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR24: c0000013aed5fc40 0000000000000002 0000000000000000 c000000002757d90
>   GPR28: c0000000000ff440 c000000002757cb8 c00000183799c1a0 c0000013aa362b00
>   NIP [c0000000000ff4d4] iommu_reconfig_notifier+0x94/0x200
>   LR [c0000000000ff4cc] iommu_reconfig_notifier+0x8c/0x200
>   Call Trace:
>   [c0000013aed5fae0] [c0000000000ff4cc] iommu_reconfig_notifier+0x8c/0x200 (unreliable)
>   [c0000013aed5fb10] [c0000000001a27b0] notifier_call_chain+0xb8/0x19c
>   [c0000013aed5fb70] [c0000000001a2a78] blocking_notifier_call_chain+0x64/0x98
>   [c0000013aed5fbb0] [c000000000c4a898] of_reconfig_notify+0x44/0xdc
>   [c0000013aed5fc20] [c000000000c4add4] of_detach_node+0x78/0xb0
>   [c0000013aed5fc70] [c0000000000f96a8] ofdt_write.part.0+0x86c/0xbb8
>   [c0000013aed5fce0] [c00000000069b4bc] proc_reg_write+0xf4/0x150
>   [c0000013aed5fd10] [c0000000005bfeb4] vfs_write+0xf8/0x488
>   [c0000013aed5fdc0] [c0000000005c0570] ksys_write+0x84/0x140
>   [c0000013aed5fe10] [c000000000033358] system_call_exception+0x138/0x330
>   [c0000013aed5fe50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec
>   --- interrupt: 3000 at 0x20000433acb4
>   <snip>
>   ---[ end trace 0000000000000000 ]---
> 
> The patch makes the iommu_group_get() call only when using it there by
> avoiding the leak.
> 
> Fixes: a8ca9fc9134c ("powerpc/iommu: Do not do platform domain attach atctions after probe")
> Reported-by: Venkat Rao Bagalkote <venkat88@xxxxxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/274e0d2b-b5cc-475e-94e6-8427e88e271d@xxxxxxxxxxxxxxxxxx
> Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>
> ---
> Changelog:
> v1: https://lore.kernel.org/all/170784021983.6249.10039296655906636112.stgit@xxxxxxxxxxxxx/
>  - Minor refactor to call the iommu_group_get() only if required.
>  - Updated the title, description and signature(Closes/Reported-by).
> 
>  arch/powerpc/kernel/iommu.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Thanks again,
Jason