Hi,

Linux 5.4.237 crashes immediately on my machine every time when the i915 driver is loaded, with an error like the one below. Previous versions are OK.

I bisected it to commit 1aed78cfda7f ("drm/i915: Don't use BAR mappings for ring buffers with LLC"). I can revert this on top of 5.4.237 and this seems sufficient to make the machine boot and work again.

Let me know if you need any more info.

Thanks, Nick

netconsole: network logging started Linux agpgart interface v0.103 fb0: switching to inteldrmfb from simple Console: switching to colour dummy device 80x25 i915 0000:00:02.0: vgaarb: deactivate vga console [drm] Supports vblank timestamp caching Rev 2 (21.10.2013). [drm] Driver supports precise vblank timestamp query. i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=io+mem:owns=io+mem BUG: kernel NULL pointer dereference, address: 000000000000007c #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 42ae34067 P4D 42ae34067 PUD 0 Oops: 0000 [#1] PREEMPT SMP CPU: 1 PID: 132 Comm: modprobe Not tainted 5.4.237 #41 Hardware name: System manufacturer System Product Name/P8H67-I DELUXE, BIOS 0907 12/04/2012 RIP: 0010:atomic_add_unless+0x0/0x1d [i915] Code: 13 06 d0 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 3d dd 0a 11 00 e9 b1 7f d1 cf 48 8b 3d d1 0a 11 00 e9 14 7a d1 cf <8b> 0f 39 ca 74 11 44 8d 04 0e 89 c8 f0 44 0f b1 07 74 04 89 c1 eb RSP: 0018:ffffb0bd401dbb08 EFLAGS: 00010202 RAX: ffffa0f26d1da500 RBX: ffffa0f26a620000 RCX: ffffa0f26d1da540 RDX: 0000000000000001 RSI: 00000000ffffffff RDI: 000000000000007c RBP: 0000000000000000 R08: ffffa0f26a700701 R09: ffffffffc03c0677 R10: ffffa0f26aceb480 R11: ffffa0f26aceb480 R12: 00000000fffffffa R13: ffffa0f26ace8100 R14: ffffa0f26a700068 R15: ffffa0f26d870000 FS: 00000000f7ce2700(0000) GS:ffffa0f26fc80000(0000) knlGS:0000000000000000 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 000000000000007c CR3: 000000042acff003 CR4: 00000000000606e0 Call Trace: intel_context_unpin+0x17/0x78 [i915] intel_engine_cleanup_common+0x97/0xc8 [i915] intel_ring_submission_init+0xbb/0xc5 [i915] ? intel_ring_submission_setup+0x2ed/0x2ed [i915] intel_engines_init+0x33/0x5b [i915] i915_gem_init+0x100/0x4c9 [i915] i915_driver_probe+0xe3b/0x1143 [i915] ? mutex_lock+0x1a/0x23 ? kernfs_activate+0x1a/0x63 pci_device_probe+0x8d/0xff really_probe+0x13b/0x2a1 driver_probe_device+0x97/0xc7 device_driver_attach+0x37/0x50 __driver_attach+0x9a/0xa3 ? device_driver_attach+0x50/0x50 bus_for_each_dev+0x5d/0x7f ? do_raw_spin_lock+0x18/0x28 bus_add_driver+0xce/0x1c6 driver_register+0x99/0xd2 ? 0xffffffffc04f6000 do_one_initcall+0x5e/0x13c ? slab_pre_alloc_hook+0x10/0x21 ? kmem_cache_alloc+0xad/0xca do_init_module+0x41/0x1c3 __do_sys_finit_module+0x7e/0x8d do_syscall_64+0x6e/0x7b entry_SYSCALL_64_after_hwframe+0x5c/0xc1 Modules linked in: i915(+) video i2c_algo_bit iosf_mbi drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm i2c_core intel_gtt agpgart netconsole ipv6 r8169 realtek libphy CR2: 000000000000007c ---[ end trace dce3967fa91cd316 ]--- RIP: 0010:atomic_add_unless+0x0/0x1d [i915] Code: 13 06 d0 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 3d dd 0a 11 00 e9 b1 7f d1 cf 48 8b 3d d1 0a 11 00 e9 14 7a d1 cf <8b> 0f 39 ca 74 11 44 8d 04 0e 89 c8 f0 44 0f b1 07 74 04 89 c1 eb RSP: 0018:ffffb0bd401dbb08 EFLAGS: 00010202 RAX: ffffa0f26d1da500 RBX: ffffa0f26a620000 RCX: ffffa0f26d1da540 RDX: 0000000000000001 RSI: 00000000ffffffff RDI: 000000000000007c RBP: 0000000000000000 R08: ffffa0f26a700701 R09: ffffffffc03c0677 R10: ffffa0f26aceb480 R11: ffffa0f26aceb480 R12: 00000000fffffffa R13: ffffa0f26ace8100 R14: ffffa0f26a700068 R15: ffffa0f26d870000 FS: 00000000f7ce2700(0000) GS:ffffa0f26fc80000(0000) knlGS:0000000000000000 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 000000000000007c CR3: 000000042acff003 CR4: 00000000000606e0 sysrq: Resetting ACPI MEMORY or I/O RESET_REG.