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Date:   Mon, 19 Oct 2020 17:36:48 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     guoren@kernel.org
Cc:     palmerdabbelt@google.com, paul.walmsley@sifive.com,
        alankao@andestech.com, rostedt@goodmis.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        anup@brainfault.org, linux-csky@vger.kernel.org,
        greentime.hu@sifive.com, zong.li@sifive.com, me@packi.ch,
        Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH v4 9/9] riscv: Fixup lockdep_assert_held(&text_mutex) in
 patch_insn_write
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On Sat, 17 Oct 2020 07:06:17 +0000
guoren@kernel.org wrote:

> From: Guo Ren <guoren@linux.alibaba.com>
> 
> It will cause warning messages:
> echo function_graph > /sys/kernel/debug/tracing/current_tracer
> [   47.691397] ------------[ cut here ]------------
> [   47.692899] WARNING: CPU: 0 PID: 11 at arch/riscv/kernel/patch.c:63 patch_insn_write+0x182/0x19a
> [   47.694483] Modules linked in:
> [   47.695754] CPU: 0 PID: 11 Comm: migration/0 Not tainted 5.9.0-11367-g1054335 #132
> [   47.698228] epc: ffffffe000204530 ra : ffffffe00020452c sp : ffffffe0023ffc20 gp : ffffffe0013e1fe0 tp : ffffffe0023e4e00 t0 : 0000000000000000
> [   47.701872]  t1 : 000000000000000e t2 : 000000000000001b s0 : ffffffe0023ffc70 s1 : ffffffe000206850 a0 : 0000000000000000 a1 : ffffffffffffffff
> [   47.705550]  a2 : 0000000000000000 a3 : ffffffe03af7c5e8 a4 : 0000000000000000 a5 : 0000000000000000 a6 : 0000000000000000 a7 : 00000000150b02d8
> [   47.709159]  s2 : 0000000000000008 s3 : 0000000000000858 s4 : ffffffe0023ffc98 s5 : 0000000000000850 s6 : 0000000000000003 s7 : 0000000000000002
> [   47.714135]  s8 : 0000000000000004 s9 : 0000000000000001 s10: 0000000000000001 s11: 0000000000000003 t3 : ffffffffffffe000 t4 : 0000000000d86254
> [   47.716574]  t5 : 0000000000000005 t6 : 0000000000040000status: 0000000000000100 badaddr: 0000000000000000 cause: 0000000000000003
> [   47.720019] CPU: 0 PID: 11 Comm: migration/0 Not tainted 5.9.0-11367-g1054335 #132
> [   47.722074] Call Trace:
> [   47.722561] [<ffffffe000203c88>] walk_stackframe+0x0/0xc2
> [   47.724608] [<ffffffe000b2020a>] show_stack+0x46/0x52
> [   47.726246] [<ffffffe000b23c24>] dump_stack+0x90/0xb6
> [   47.727672] [<ffffffe00020c9c4>] __warn+0x98/0xfa
> [   47.729131] [<ffffffe0005f4be0>] report_bug+0xaa/0x11e
> [   47.730624] [<ffffffe000203b74>] do_trap_break+0x96/0xfe
> [   47.732448] [<ffffffe000201daa>] ret_from_exception+0x0/0x14
> [   47.734341] [<ffffffe00020452c>] patch_insn_write+0x17e/0x19a
> [   47.737235] irq event stamp: 39
> [   47.738521] hardirqs last  enabled at (39): [<ffffffe000201d0a>] _save_context+0xa2/0xe6
> [   47.741055] hardirqs last disabled at (38): [<ffffffe0002c2404>] multi_cpu_stop+0x130/0x166
> [   47.743551] softirqs last  enabled at (0): [<ffffffe00020a4d2>] copy_process+0x430/0x1316
> [   47.746031] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [   47.748617] ---[ end trace 88a1054faa6524ef ]---
> 
> Because the path of stop_machine(__ftrace_modify_code)->
> ftrace_modify_all_code->...->patch_insn_write has no pair of
> lock&unlock text_mutex, so we shouldn't put assert here.

Hm, are there any chance to get the text_mutex in that path?
There are ftrace_arch_code_modify_prepare/post_process() in arch/riscv/kernel/ftrace.c,
aren't those used?

Thank you,

> 
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> ---
>  arch/riscv/kernel/patch.c | 7 -------
>  1 file changed, 7 deletions(-)
> 
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 0b55287..2ee5063 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -55,13 +55,6 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
>  	bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
>  	int ret;
>  
> -	/*
> -	 * Before reaching here, it was expected to lock the text_mutex
> -	 * already, so we don't need to give another lock here and could
> -	 * ensure that it was safe between each cores.
> -	 */
> -	lockdep_assert_held(&text_mutex);
> -
>  	if (across_pages)
>  		patch_map(addr + len, FIX_TEXT_POKE1);
>  
> -- 
> 2.7.4
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>