When gvt debug fs is destroyed, need to have a sane check if drm minor's debugfs root is still available or not, otherwise in case like device remove through unbinding, drm minor's debugfs directory has already been removed, then intel_gvt_debugfs_clean() would act upon dangling pointer like below oops.
i915 0000:00:02.0: Direct firmware load for i915/gvt/vid_0x8086_did_0x1926_rid_0x0a.golden_hw_state failed with error -2 i915 0000:00:02.0: MDEV: Registered Console: switching to colour dummy device 80x25 i915 0000:00:02.0: MDEV: Unregistering BUG: kernel NULL pointer dereference, address: 00000000000000a0 PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT SMP PTI CPU: 2 PID: 2486 Comm: gfx-unbind.sh Tainted: G I 6.1.0-rc8+ #15 Hardware name: Dell Inc. XPS 13 9350/0JXC1H, BIOS 1.13.0 02/10/2020 RIP: 0010:down_write+0x1f/0x90 Code: 1d ff ff 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53 48 89 fb e8 62 c0 ff ff bf 01 00 00 00 e8 28 5e 31 ff 31 c0 ba 01 00 00 00 <f0> 48 0f b1 13 75 33 65 48 8b 04 25 c0 bd 01 00 48 89 43 08 bf 01 RSP: 0018:ffff9eb3036ffcc8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 00000000000000a0 RCX: ffffff8100000000 RDX: 0000000000000001 RSI: 0000000000000064 RDI: ffffffffa48787a8 RBP: ffff9eb3036ffd30 R08: ffffeb1fc45a0608 R09: ffffeb1fc45a05c0 R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000 R13: ffff91acc33fa328 R14: ffff91acc033f080 R15: ffff91acced533e0 FS: 00007f6947bba740(0000) GS:ffff91ae36d00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000000a0 CR3: 00000001133a2002 CR4: 00000000003706e0 Call Trace: <TASK> simple_recursive_removal+0x9f/0x2a0 ? start_creating.part.0+0x120/0x120 ? _raw_spin_lock+0x13/0x40 debugfs_remove+0x40/0x60 intel_gvt_debugfs_clean+0x15/0x30 [kvmgt] intel_gvt_clean_device+0x49/0xe0 [kvmgt] intel_gvt_driver_remove+0x2f/0xb0 i915_driver_remove+0xa4/0xf0 i915_pci_remove+0x1a/0x30 pci_device_remove+0x33/0xa0 device_release_driver_internal+0x1b2/0x230 unbind_store+0xe0/0x110 kernfs_fop_write_iter+0x11b/0x1f0 vfs_write+0x203/0x3d0 ksys_write+0x63/0xe0 do_syscall_64+0x37/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f6947cb5190 Code: 40 00 48 8b 15 71 9c 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d 51 24 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89 RSP: 002b:00007ffcbac45a28 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 000000000000000d RCX: 00007f6947cb5190 RDX: 000000000000000d RSI: 0000555e35c866a0 RDI: 0000000000000001 RBP: 0000555e35c866a0 R08: 0000000000000002 R09: 0000555e358cb97c R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000001 R13: 000000000000000d R14: 0000000000000000 R15: 0000555e358cb8e0 </TASK> Modules linked in: kvmgt CR2: 00000000000000a0 ---[ end trace 0000000000000000 ]---
Cc: Wang, Zhi zhi.a.wang@intel.com Cc: He, Yu yu.he@intel.com Cc: stable@vger.kernel.org Reviewed-by: Zhi Wang zhi.a.wang@intel.com Fixes: bc7b0be316ae ("drm/i915/gvt: Add basic debugfs infrastructure") Signed-off-by: Zhenyu Wang zhenyuw@linux.intel.com --- drivers/gpu/drm/i915/gvt/debugfs.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c index 9f1c209d9251..d7df27feee8c 100644 --- a/drivers/gpu/drm/i915/gvt/debugfs.c +++ b/drivers/gpu/drm/i915/gvt/debugfs.c @@ -199,6 +199,10 @@ void intel_gvt_debugfs_init(struct intel_gvt *gvt) */ void intel_gvt_debugfs_clean(struct intel_gvt *gvt) { - debugfs_remove_recursive(gvt->debugfs_root); - gvt->debugfs_root = NULL; + struct drm_minor *minor = gvt->gt->i915->drm.primary; + + if (minor->debugfs_root) { + debugfs_remove_recursive(gvt->debugfs_root); + gvt->debugfs_root = NULL; + } }