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From:   Changbin Du <changbin.du@gmail.com>
To:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Changbin Du <changbin.du@gmail.com>
Subject: [PATCH] riscv: patch: remove lockdep assertion on lock text_mutex
Date:   Sat, 17 Apr 2021 10:35:32 +0800
Message-Id: <20210417023532.354714-1-changbin.du@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The function patch_insn_write() expects that the text_mutex is already
held. There's a case that text_mutex is acquired by ftrace_run_update_code()
under syscall context but then patch_insn_write() will be executed under the
migration kthread context as we involves stop machine. So we should remove
the assertion, or it can cause warning storm in kernel message.

[  104.641978] ------------[ cut here ]------------
[  104.642327] WARNING: CPU: 0 PID: 13 at arch/riscv/kernel/patch.c:63 patch_insn_write+0x166/0x17c
[  104.643587] Modules linked in:
[  104.644691] CPU: 0 PID: 13 Comm: migration/0 Not tainted 5.12.0-rc7-00067-g9cdbf6467424 #102
[  104.644907] Hardware name: riscv-virtio,qemu (DT)
[  104.645068] Stopper: multi_cpu_stop+0x0/0x17e <- 0x0
[  104.645349] epc : patch_insn_write+0x166/0x17c
[  104.645467]  ra : patch_insn_write+0x162/0x17c
[  104.645534] epc : ffffffe0000059c6 ra : ffffffe0000059c2 sp : ffffffe002a33c70
[  104.645580]  gp : ffffffe0019e5518 tp : ffffffe002a232c0 t0 : ffffffe01295e8a8
[  104.645622]  t1 : 0000000000000001 t2 : 0000000000000000 s0 : ffffffe002a33cc0
[  104.645675]  s1 : ffffffe000007f72 a0 : 0000000000000000 a1 : ffffffffffffffff
[  104.645716]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : 0000000000000001
[  104.645757]  a5 : ffffffe0799e45c8 a6 : 00000000000ca097 a7 : 0000000000000000
[  104.645798]  s2 : 0000000000000008 s3 : 0000000000000f72 s4 : ffffffe002a33ce0
[  104.645839]  s5 : 0000000000000f7a s6 : 0000000000000003 s7 : 0000000000000003
[  104.645880]  s8 : 0000000000000004 s9 : 0000000000000002 s10: 0000000000000000
[  104.645920]  s11: 0000000000000002 t3 : 0000000000000001 t4 : ffffffe000c615c8
[  104.645958]  t5 : 0000000000007fff t6 : 0000000000000380
[  104.645998] status: 0000000000000100 badaddr: 0000000000000000 cause: 0000000000000003
[  104.646081] Call Trace:
[  104.646147] [<ffffffe0000059c6>] patch_insn_write+0x166/0x17c
[  104.646280] [<ffffffe0000059ec>] patch_text_nosync+0x10/0x32
[  104.646317] [<ffffffe000007d0c>] ftrace_update_ftrace_func+0x74/0xac
[  104.646352] [<ffffffe0000d338a>] ftrace_modify_all_code+0x9c/0x144
[  104.646387] [<ffffffe0000d3444>] __ftrace_modify_code+0x12/0x1c
[  104.646420] [<ffffffe0000c4c2c>] multi_cpu_stop+0xa8/0x17e
[  104.646451] [<ffffffe0000c4474>] cpu_stopper_thread+0xb2/0x156
[  104.646489] [<ffffffe00003645e>] smpboot_thread_fn+0x102/0x1ea
[  104.646524] [<ffffffe0000311b0>] kthread+0x132/0x148
[  104.646556] [<ffffffe000002e02>] ret_from_exception+0x0/0x14
[  104.646657] ---[ end trace ccf71babb9de4d5b ]---
[  104.647444] ------------[ cut here ]------------

Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
 arch/riscv/kernel/patch.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 0b552873a577..6d2ed9c15065 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -49,19 +49,18 @@ static void patch_unmap(int fixmap)
 }
 NOKPROBE_SYMBOL(patch_unmap);
 
+
+/*
+ * 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.
+ */
 static int patch_insn_write(void *addr, const void *insn, size_t len)
 {
 	void *waddr = addr;
 	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);
 
-- 
2.27.0