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>>> -        if (!num_in_sync && xe_sync_needs_wait(&syncs[num_syncs])) >>> +        if (!num_in_sync && syncs[num_syncs].fence && >>> +            xe_sync_needs_wait(&syncs[num_syncs])) >> >> In xe_sync_entry_parse() it looks like it will always populate the >> fence for the !signal case, otherwise throwing an error if that is >> not possible. And xe_sync_needs_wait() will only touch the fence if >> it's the signal case? So it seems like this should not be possible? > > Sorry meant to type: > > s/touch the fence if it's the signal/touch the fence if it's the !signal/ > I'm not sure of the complete flow but it is quite easy to reproduce. Here is the stacktrace snippet: [  118.410401] RIP: 0010:xe_sync_needs_wait+0x27/0x50 [xe] [  118.410940] Code: 90 90 90 0f 1f 44 00 00 55 48 89 f1 48 89 e5 48 83 ec 08 48 83 7e 08 00 0f 84 79 be 1c 00 31 c0 f6 41 4c 01 75 11 48 8b 41 08 <48> 8b 40 30 48 d1 e8 83 e0 01 83 f0 01 c9 31 d2 31 c9 31 f6 31 ff [  118.410949] RSP: 0018:ffffccec8ea7bb18 EFLAGS: 00010246 [  118.410957] RAX: 0000000000000000 RBX: 00007ff23812f460 RCX: ffff8c1790db4800 [  118.410964] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 [  118.410968] RBP: ffffccec8ea7bb20 R08: 0000000000000000 R09: 0000000000000000 [  118.410973] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8c1790db4800 [  118.410978] R13: 0000000000000000 R14: ffff8c178b67e000 R15: 0000000000000000 [  118.410984] FS:  0000000101aff6c0(0000) GS:ffff8c27350d1000(0000) knlGS:000000007fe20000 [  118.410992] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [  118.410998] CR2: 0000000000000030 CR3: 00000001037ef005 CR4: 0000000000772ef0 [  118.411004] PKRU: 55555554 [  118.411008] Call Trace: [  118.411013]  [  118.411022]  xe_exec_ioctl+0x375/0xea0 [xe] [  118.411377]  ? __x64_sys_ioctl+0xbd/0x100 [  118.411392]  ? do_syscall_64+0xa7/0x580 [  118.411403]  ? dma_fence_free+0x1a/0x30 [  118.411419]  ? __pfx_xe_exec_fn+0x10/0x10 [xe] [  118.411752]  ? drm_syncobj_array_free+0x56/0x80 [drm] [  118.411915]  ? drm_syncobj_query_ioctl+0x20f/0x460 [drm] [  118.412035]  ? __pfx_xe_exec_ioctl+0x10/0x10 [xe] [  118.412372]  drm_ioctl_kernel+0xae/0x110 [drm] [  118.412524]  drm_ioctl+0x2ee/0x5d0 [drm] [  118.412649]  ? __pfx_xe_exec_ioctl+0x10/0x10 [xe] [  118.412989]  ? __pm_runtime_resume+0x5f/0x90 [  118.413002]  xe_drm_ioctl+0x61/0xb0 [xe] [  118.413329]  __x64_sys_ioctl+0xa3/0x100 [  118.413338]  x64_sys_call+0x1060/0x2360 [  118.413347]  do_syscall_64+0x74/0x580 [  118.413355]  ? x64_sys_call+0x1060/0x2360 [  118.413360]  ? do_syscall_64+0xa7/0x580 [  118.413368]  ? __do_sys_getpid+0x1d/0x30 [  118.413377]  ? x64_sys_call+0xf9d/0x2360 [  118.413383]  ? do_syscall_64+0xa7/0x580 [  118.413389]  ? x64_sys_call+0x1060/0x2360 [  118.413395]  ? do_syscall_64+0xa7/0x580 [  118.413401]  ? sysvec_apic_timer_interrupt+0x54/0xd0 [  118.413410]  entry_SYSCALL_64_after_hwframe+0x76/0x7e [  118.413418] RIP: 0033:0x7ff29c93287d >> >>>               num_in_sync++; >>>       } >> >