linux-kernel - [PATCH v4 9/9] riscv: Fixup lockdep_assert_held(&text_mutex) in patch_insn

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Message-Id: <1602918377-23573-10-git-send-email-guoren@kernel.org>
Date:   Sat, 17 Oct 2020 07:06:17 +0000
From:   guoren@...nel.org
To:     palmerdabbelt@...gle.com, paul.walmsley@...ive.com,
        mhiramat@...nel.org, alankao@...estech.com, rostedt@...dmis.org
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        anup@...infault.org, linux-csky@...r.kernel.org,
        greentime.hu@...ive.com, zong.li@...ive.com, guoren@...nel.org,
        me@...ki.ch, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH v4 9/9] riscv: Fixup lockdep_assert_held(&text_mutex) in patch_insn_write

From: Guo Ren <guoren@...ux.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.

Signed-off-by: Guo Ren <guoren@...ux.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