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SubjectRe: [PATCH] RISC-V: insn: Use a raw spinlock to protect TEXT_POKE*
On Fri, 30 Apr 2021 05:54:51 +0800
Changbin Du <changbin.du@gmail.com> wrote:

> The problem is that lockdep cannot handle locks across tasks since we use
> stopmachine to patch code for risc-v. So there's a false positive report.
> See privious disscussion here:

> https://lkml.org/lkml/2021/4/29/63

Please use lore.kernel.org, lkml.org is highly unreliable, and is
considered deprecated for use of referencing linux kernel archives.

Would the following patch work?

(note, I did not even compile test it)

-- Steve

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 845002cc2e57..19acbb4aaeff 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -25,6 +25,8 @@ struct dyn_arch_ftrace {
};
#endif

+extern int running_ftrace;
+
#ifdef CONFIG_DYNAMIC_FTRACE
/*
* A general call in RISC-V is a pair of insts:
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 7f1e5203de88..834ab4fad637 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -11,15 +11,19 @@
#include <asm/cacheflush.h>
#include <asm/patch.h>

+int running_ftrace;
+
#ifdef CONFIG_DYNAMIC_FTRACE
int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
{
mutex_lock(&text_mutex);
+ running_ftrace = 1;
return 0;
}

int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
{
+ running_ftrace = 0;
mutex_unlock(&text_mutex);
return 0;
}
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 0b552873a577..4cd1c79a9689 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -12,6 +12,7 @@
#include <asm/cacheflush.h>
#include <asm/fixmap.h>
#include <asm/patch.h>
+#include <asm/ftrace.h>

struct patch_insn {
void *addr;
@@ -59,8 +60,13 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
* 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.
+ *
+ * ftrace uses stop machine, and even though the text_mutex is
+ * held, the stop machine task that calls this function will not
+ * be the owner.
*/
- lockdep_assert_held(&text_mutex);
+ if (!running_ftrace)
+ lockdep_assert_held(&text_mutex);

if (across_pages)
patch_map(addr + len, FIX_TEXT_POKE1);
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