Am Dienstag, dem 09.04.2024 um 10:34 +1000 schrieb Dave Airlie: > From: Dave Airlie <airlied@xxxxxxxxxx> > > Running a lot of VK CTS in parallel against nouveau, once every > few hours you might see something like this crash. > > BUG: kernel NULL pointer dereference, address: 0000000000000008 > PGD 8000000114e6e067 P4D 8000000114e6e067 PUD 109046067 PMD 0 > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 7 PID: 53891 Comm: deqp-vk Not tainted 6.8.0-rc6+ #27 > Hardware name: Gigabyte Technology Co., Ltd. Z390 I AORUS PRO WIFI/Z390 I AORUS PRO WIFI-CF, BIOS F8 11/05/2021 > RIP: 0010:gp100_vmm_pgt_mem+0xe3/0x180 [nouveau] > Code: c7 48 01 c8 49 89 45 58 85 d2 0f 84 95 00 00 00 41 0f b7 46 12 49 8b 7e 08 89 da 42 8d 2c f8 48 8b 47 08 41 83 c7 01 48 89 ee <48> 8b 40 08 ff d0 0f 1f 00 49 8b 7e 08 48 89 d9 48 8d 75 04 48 c1 > RSP: 0000:ffffac20c5857838 EFLAGS: 00010202 > RAX: 0000000000000000 RBX: 00000000004d8001 RCX: 0000000000000001 > RDX: 00000000004d8001 RSI: 00000000000006d8 RDI: ffffa07afe332180 > RBP: 00000000000006d8 R08: ffffac20c5857ad0 R09: 0000000000ffff10 > R10: 0000000000000001 R11: ffffa07af27e2de0 R12: 000000000000001c > R13: ffffac20c5857ad0 R14: ffffa07a96fe9040 R15: 000000000000001c > FS: 00007fe395eed7c0(0000) GS:ffffa07e2c980000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000008 CR3: 000000011febe001 CR4: 00000000003706f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > > ... > > ? gp100_vmm_pgt_mem+0xe3/0x180 [nouveau] > ? gp100_vmm_pgt_mem+0x37/0x180 [nouveau] > nvkm_vmm_iter+0x351/0xa20 [nouveau] > ? __pfx_nvkm_vmm_ref_ptes+0x10/0x10 [nouveau] > ? __pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] > ? __pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] > ? __lock_acquire+0x3ed/0x2170 > ? __pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] > nvkm_vmm_ptes_get_map+0xc2/0x100 [nouveau] > ? __pfx_nvkm_vmm_ref_ptes+0x10/0x10 [nouveau] > ? __pfx_gp100_vmm_pgt_mem+0x10/0x10 [nouveau] > nvkm_vmm_map_locked+0x224/0x3a0 [nouveau] > > Adding any sort of useful debug usually makes it go away, so I hand > wrote the function in a line, and debugged the asm. > > Every so often pt->memory->ptrs is NULL. This ptrs ptr is set in > the nv50_instobj_acquire called from nvkm_kmap. > > If Thread A and Thread B both get to nv50_instobj_acquire around > the same time, and Thread A hits the refcount_set line, and in > lockstep thread B succeeds at refcount_inc_not_zero, there is a > chance the ptrs value won't have been stored since refcount_set > is unordered. Force a memory barrier here, I picked smp_mb, since > we want it on all CPUs and it's write followed by a read. > > Cc: linux-stable > Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx> > --- > drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c b/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c > index a7f3fc342d87..cbacc7b11f8c 100644 > --- a/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c > +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c > @@ -250,6 +250,9 @@ nv50_instobj_acquire(struct nvkm_memory *memory) > iobj->base.memory.ptrs = &nv50_instobj_fast; > else > iobj->base.memory.ptrs = &nv50_instobj_slow; > + /* barrier to ensure ptrs is written before another thread > + does refcount_inc_not_zero successfully. */ > + smp_mb(); Doesn't this miss the corresponding smp_rmb after refcount_inc_not_zero? Without it a sufficiently speculating CPU might still hoist the NULL ptr load across the refcount increase. Regards, Lucas
