Re: [PATCH v2 2/2] tracing/kprobe: Add kprobe_event= boot parameter

From: Anders Roxell <anders.roxell@linaro.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S . Miller" <davem@davemloft.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-doc@vger.kernel.org
Subject: Re: [PATCH v2 2/2] tracing/kprobe: Add kprobe_event= boot parameter
Date: Tue, 28 May 2019 14:23:43 +0200	[thread overview]
Message-ID: <CADYN=9KHQPQTgy==TYZ5iD_zViPbHq4hgOUwuX69aQWV6vZOQg@mail.gmail.com> (raw)
In-Reply-To: <155851395498.15728.830529496248543583.stgit@devnote2>

On Wed, 22 May 2019 at 10:32, Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> Add kprobe_event= boot parameter to define kprobe events
> at boot time.
> The definition syntax is similar to tracefs/kprobe_events
> interface, but use ',' and ';' instead of ' ' and '\n'
> respectively. e.g.
>
>   kprobe_event=p,vfs_read,$arg1,$arg2
>
> This puts a probe on vfs_read with argument1 and 2, and
> enable the new event.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

I built an arm64 kernel from todays linux-next tag next-20190528 and
ran in to this issue when I booted it up in qemu:

[    9.068772][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.2.0-rc2-next-20190528-00019-g9a6008710716 #8
[    9.072893][    T1] Hardware name: linux,dummy-virt (DT)
[    9.075143][    T1] pstate: 80400005 (Nzcv daif +PAN -UAO)
[    9.077528][    T1] pc : kprobe_target+0x0/0x30
[    9.079479][    T1] lr : init_test_probes+0x134/0x540
[    9.081611][    T1] sp : ffff80003f51fbe0
[    9.083331][    T1] x29: ffff80003f51fbe0 x28: ffff200013c17820
[    9.085906][    T1] x27: ffff200015d3ab40 x26: ffff2000122bb120
[    9.088491][    T1] x25: 0000000000000000 x24: ffff200013c08ae0
[    9.091068][    T1] x23: ffff200015d39000 x22: ffff200013a15ac8
[    9.093667][    T1] x21: 1ffff00007ea3f86 x20: ffff200015d39420
[    9.096214][    T1] x19: ffff2000122bad20 x18: 0000000000001400
[    9.098831][    T1] x17: 0000000000000000 x16: ffff80003f510040
[    9.101410][    T1] x15: 0000000000001480 x14: 1ffff00007ea3ea2
[    9.103963][    T1] x13: 00000000f1f1f1f1 x12: ffff040002782e0d
[    9.106549][    T1] x11: 1fffe40002782e0c x10: ffff040002782e0c
[    9.109120][    T1] x9 : 1fffe40002782e0c x8 : dfff200000000000
[    9.111676][    T1] x7 : ffff040002782e0d x6 : ffff200013c17067
[    9.114234][    T1] x5 : ffff80003f510040 x4 : 0000000000000000
[    9.116843][    T1] x3 : ffff200010427508 x2 : 0000000000000000
[    9.119409][    T1] x1 : ffff200010426e10 x0 : 0000000000a6326b
[    9.121980][    T1] Call trace:
[    9.123380][    T1]  kprobe_target+0x0/0x30
[    9.125205][    T1]  init_kprobes+0x2b8/0x300
[    9.127074][    T1]  do_one_initcall+0x4c0/0xa68
[    9.129076][    T1]  kernel_init_freeable+0x3c4/0x4e4
[    9.131234][    T1]  kernel_init+0x14/0x1fc
[    9.133032][    T1]  ret_from_fork+0x10/0x18
[    9.134908][    T1] Code: a9446bf9 f9402bfb a8d87bfd d65f03c0 (d4200080)
[    9.137845][    T1] ---[ end trace 49243ee03446b072 ]---
[    9.140114][    T1] Kernel panic - not syncing: Fatal exception
[    9.142684][    T1] ---[ end Kernel panic - not syncing: Fatal exception ]---

I bisected down to this commit as the one that introduces this issue.
I'm unsure why this causes the call trace though, any ideas?

Cheers,
Anders