While running kselftest on i386 on Linux next 20201001 kernel this bug was noticed. BUG: kernel NULL pointer dereference, address: 00000024

steps to reproduce: # cd /opt/kselftests/ftrace # ./ftracetest

metadata: git branch: master git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git git commit: d39294091fee6b89d9c4a683bb19441b25098330 git describe: next-20201001ftracetest make_kernelversion: 5.9.0-rc7 kernel-config: http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-core2-32/lkft/...

# selftests: ftrace: ftracetest # === Ftrace unit tests === # [1] Basic trace file check [PASS] # [2] Basic test for tracers [PASS] # [3] Basic trace clock test [PASS] # [4] Basic event tracing check [PASS] # [5] Change the ringbuffer size [PASS] # [6] Snapshot and tracing setting [PASS] # [7] trace_pipe and trace_marker [PASS] # [8] Test ftrace direct functions against tracers [UNRESOLVED] # [9] Test ftrace direct functions against kprobes [UNRESOLVED] # [10] Generic dynamic event - add/remove kprobe events [PASS] # [11] Generic dynamic event - add/remove synthetic events [PASS] # [12] Generic dynamic event - selective clear (compatibility) [PASS] # [13] Generic dynamic event - generic clear event [PASS] # [14] event tracing - enable/disable with event level files [ 207.481763] BUG: kernel NULL pointer dereference, address: 00000024 [ 207.488050] #PF: supervisor read access in kernel mode [ 207.493205] #PF: error_code(0x0000) - not-present page [ 207.498355] *pde = 00000000 [ 207.501258] Oops: 0000 [#1] SMP [ 207.504421] CPU: 2 PID: 0 Comm: swapper/2 Tainted: G W 5.9.0-rc7-next-20201001 #1 [ 207.513205] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS 2.0b 07/27/2017 [ 207.520680] EIP: trace_event_raw_event_sched_switch+0x10/0x180 [ 207.526510] Code: 08 5b 5e 5f 5d c3 8d 74 26 00 31 c0 eb e4 e8 27 1d de 00 8d b4 26 00 00 00 00 55 89 e5 57 56 53 89 c6 89 cf 83 ec 28 8b 45 08 <8b> 5e 24 89 55 cc 89 45 d0 65 a1 14 00 00 00 89 45 f0 31 c0 f6 c7 [ 207.545253] EAX: f55aa480 EBX: f55aa480 ECX: f55adb40 EDX: 00000000 [ 207.551510] ESI: 00000000 EDI: f55adb40 EBP: f55bbf20 ESP: f55bbeec [ 207.557769] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00210092 [ 207.564554] CR0: 80050033 CR2: 00000024 CR3: 10830000 CR4: 003506d0 [ 207.570811] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 [ 207.577069] DR6: fffe0ff0 DR7: 00000400 [ 207.580898] Call Trace: [ 207.583344] ? pick_next_task_fair+0x165/0x3b0 [ 207.587794] __schedule+0x4dc/0xa90 [ 207.591283] schedule_idle+0x1c/0x40 [ 207.594863] do_idle+0x185/0x2a0 [ 207.598097] cpu_startup_entry+0x25/0x30 [ 207.602021] start_secondary+0x106/0x140 [ 207.605946] startup_32_smp+0x164/0x168 [ 207.609778] Modules linked in: sch_fq sch_ingress veth algif_hash x86_pkg_temp_thermal fuse [last unloaded: test_bpf] [ 207.620385] CR2: 0000000000000024 [ 207.623697] ---[ end trace 6ad815a56bdaaf71 ]--- [ 207.628342] EIP: trace_event_raw_event_sched_switch+0x10/0x180 [ 207.634173] Code: 08 5b 5e 5f 5d c3 8d 74 26 00 31 c0 eb e4 e8 27 1d de 00 8d b4 26 00 00 00 00 55 89 e5 57 56 53 89 c6 89 cf 83 ec 28 8b 45 08 <8b> 5e 24 89 55 cc 89 45 d0 65 a1 14 00 00 00 89 45 f0 31 c0 f6 c7 [ 207.652918] EAX: f55aa480 EBX: f55aa480 ECX: f55adb40 EDX: 00000000 [ 207.659175] ESI: 00000000 EDI: f55adb40 EBP: f55bbf20 ESP: f55bbeec [ 207.665433] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00210092 [ 207.672211] CR0: 80050033 CR2: 00000024 CR3: 10830000 CR4: 003506d0 [ 207.678466] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 [ 207.684740] DR6: fffe0ff0 DR7: 00000400 [ 207.688597] Kernel panic - not syncing: Attempted to kill the idle task! [ 207.695329] Kernel Offset: disabled [ 207.698828] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

full test log, https://lkft.validation.linaro.org/scheduler/job/1809544#L6012