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

[Shivaprasad G Bhat <sbhat@linux.ibm.com>]

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@linux.vnet.ibm.com>
Closes: https://lore.kernel.org/all/274e0d2b-b5cc-475e-94e6-8427e88e271d@linux.vnet.ibm.com
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
---
Changelog:
v1: https://lore.kernel.org/all/170784021983.6249.10039296655906636112.stgit@linux.ibm.com/
 - 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(-)

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index d71eac3b2887..37fae3bd89c6 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -1285,13 +1285,14 @@ spapr_tce_platform_iommu_attach_dev(struct iommu_domain *platform_domain,
 				    struct device *dev)
 {
 	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
-	struct iommu_group *grp = iommu_group_get(dev);
 	struct iommu_table_group *table_group;
+	struct iommu_group *grp;

 	/* At first attach the ownership is already set */
 	if (!domain)
 		return 0;

+	grp = iommu_group_get(dev);
 	table_group = iommu_group_get_iommudata(grp);
 	/*
 	 * The domain being set to PLATFORM from earlier