Re: [PATCH 2/4] ftrace/instances: Clear function triggers when removing instances

[Steven Rostedt]

On Sun, 14 May 2017 01:01:02 +0530
"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote:

> If instance directories are deleted while there are registered function
> triggers:
> 
>   # cd /sys/kernel/debug/tracing/instances
>   # mkdir test
>   # echo "schedule:enable_event:sched:sched_switch" > test/set_ftrace_filter
>   # rmdir test
>   Unable to handle kernel paging request for data at address 0x00000008
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc0000000021edde8
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   SMP NR_CPUS=2048
>   NUMA
>   pSeries
>   Modules linked in: iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_tcpudp tun bridge stp llc kvm iptable_filter fuse binfmt_misc pseries_rng rng_core vmx_crypto ib_iser rdma_cm iw_cm ib_cm ib_core libiscsi scsi_transport_iscsi ip_tables x_tables autofs4 btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c multipath virtio_net virtio_blk virtio_pci crc32c_vpmsum virtio_ring virtio
>   CPU: 8 PID: 8694 Comm: rmdir Not tainted 4.11.0-nnr+ #113
>   task: c0000000bab52800 task.stack: c0000000baba0000
>   NIP: c0000000021edde8 LR: c0000000021f0590 CTR: c000000002119620
>   REGS: c0000000baba3870 TRAP: 0300   Not tainted  (4.11.0-nnr+)
>   MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE>
>     CR: 22002422  XER: 20000000
>   CFAR: 00007fffabb725a8 DAR: 0000000000000008 DSISR: 40000000 SOFTE: 0
>   GPR00: c00000000220f750 c0000000baba3af0 c000000003157e00 0000000000000000
>   GPR04: 0000000000000040 00000000000000eb 0000000000000040 0000000000000000
>   GPR08: 0000000000000000 0000000000000113 0000000000000000 c00000000305db98
>   GPR12: c000000002119620 c00000000fd42c00 0000000000000000 0000000000000000
>   GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR20: 0000000000000000 0000000000000000 c0000000bab52e90 0000000000000000
>   GPR24: 0000000000000000 00000000000000eb 0000000000000040 c0000000baba3bb0
>   GPR28: c00000009cb06eb0 c0000000bab52800 c00000009cb06eb0 c0000000baba3bb0
>   NIP [c0000000021edde8] ring_buffer_lock_reserve+0x8/0x4e0
>   LR [c0000000021f0590] trace_event_buffer_lock_reserve+0xe0/0x1a0
>   Call Trace:
>   [c0000000baba3af0] [c0000000021f96c8] trace_event_buffer_commit+0x1b8/0x280 (unreliable)
>   [c0000000baba3b60] [c00000000220f750] trace_event_buffer_reserve+0x80/0xd0
>   [c0000000baba3b90] [c0000000021196b8] trace_event_raw_event_sched_switch+0x98/0x180
>   [c0000000baba3c10] [c0000000029d9980] __schedule+0x6e0/0xab0
>   [c0000000baba3ce0] [c000000002122230] do_task_dead+0x70/0xc0
>   [c0000000baba3d10] [c0000000020ea9c8] do_exit+0x828/0xd00
>   [c0000000baba3dd0] [c0000000020eaf70] do_group_exit+0x60/0x100
>   [c0000000baba3e10] [c0000000020eb034] SyS_exit_group+0x24/0x30
>   [c0000000baba3e30] [c00000000200bcec] system_call+0x38/0x54
>   Instruction dump:
>   60000000 60420000 7d244b78 7f63db78 4bffaa09 393efff8 793e0020 39200000
>   4bfffecc 60420000 3c4c00f7 3842a020 <81230008> 2f890000 409e02f0 a14d0008
>   ---[ end trace b917b8985d0e650b ]---
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc0000000021edde8
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc0000000021edde8
>   Faulting instruction address: 0xc0000000021edde8
> 
> To address this, let's clear all registered function probes before
> deleting the ftrace instance.
> 
> Reported-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> ---
>  kernel/trace/ftrace.c | 8 ++++++++
>  kernel/trace/trace.c  | 1 +
>  kernel/trace/trace.h  | 1 +
>  3 files changed, 10 insertions(+)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 28dc824ad072..1b96d927a082 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4256,6 +4256,14 @@ unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr,
>  	return ret;
>  }
>  
> +void clear_ftrace_function_probes(struct trace_array *tr)
> +{
> +	struct ftrace_func_probe *probe, *n;
> +
> +	list_for_each_entry_safe(probe, n, &tr->func_probes, list)
> +		unregister_ftrace_function_probe_func(NULL, tr, probe->probe_ops);
> +}
> +
>  static LIST_HEAD(ftrace_commands);
>  static DEFINE_MUTEX(ftrace_cmd_mutex);
>  
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c4536c449021..3f2aed4ad1ed 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -7550,6 +7550,7 @@ static int instance_rmdir(const char *name)
>  	}
>  
>  	tracing_set_nop(tr);
> +	clear_ftrace_function_probes(tr);
>  	event_trace_del_tracer(tr);
>  	ftrace_clear_pids(tr);
>  	ftrace_destroy_function_files(tr);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 291a1bca5748..98e0845f7235 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -980,6 +980,7 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
>  extern int
>  unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr,
>  				      struct ftrace_probe_ops *ops);
> +extern void clear_ftrace_function_probes(struct trace_array *tr);

This needs to have a stub function when CONFIG_DYNAMIC_FTRACE is not
defined. Otherwise we have:

kernel/trace/trace.c:7553:2: error: implicit declaration of function 'clear_ftrace_function_probes' [-Werror=implicit-function-declaration]
  clear_ftrace_function_probes(tr);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

-- Steve

>  
>  int register_ftrace_command(struct ftrace_func_command *cmd);
>  int unregister_ftrace_command(struct ftrace_func_command *cmd);