4 files changed, 41 insertions, 6 deletions

diff --git a/arch/riscv/kernel/compat_vdso/Makefile b/arch/riscv/kernel/compat_vdso/Makefile
index 260daf3236d3..7f34f3c7c882 100644
--- a/arch/riscv/kernel/compat_vdso/Makefile
+++ b/arch/riscv/kernel/compat_vdso/Makefile
@@ -14,6 +14,10 @@ COMPAT_LD := $(LD)
 COMPAT_CC_FLAGS := -march=rv32g -mabi=ilp32
 COMPAT_LD_FLAGS := -melf32lriscv
 
+# Disable attributes, as they're useless and break the build.
+COMPAT_CC_FLAGS += $(call cc-option,-mno-riscv-attribute)
+COMPAT_CC_FLAGS += $(call as-option,-Wa$(comma)-mno-arch-attr)
+
 # Files to link into the compat_vdso
 obj-compat_vdso = $(patsubst %, %.o, $(compat_vdso-syms)) note.o
 
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 5bff37af4770..03a6434a8cdd 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -15,10 +15,19 @@
 void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
 {
 	mutex_lock(&text_mutex);
+
+	/*
+	 * The code sequences we use for ftrace can't be patched while the
+	 * kernel is running, so we need to use stop_machine() to modify them
+	 * for now.  This doesn't play nice with text_mutex, we use this flag
+	 * to elide the check.
+	 */
+	riscv_patch_in_stop_machine = true;
 }
 
 void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
 {
+	riscv_patch_in_stop_machine = false;
 	mutex_unlock(&text_mutex);
 }
 
@@ -107,9 +116,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 {
 	int out;
 
-	ftrace_arch_code_modify_prepare();
+	mutex_lock(&text_mutex);
 	out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
-	ftrace_arch_code_modify_post_process();
+	mutex_unlock(&text_mutex);
 
 	return out;
 }
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 8086d1a281cd..575e71d6c8ae 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -11,6 +11,7 @@
 #include <asm/kprobes.h>
 #include <asm/cacheflush.h>
 #include <asm/fixmap.h>
+#include <asm/ftrace.h>
 #include <asm/patch.h>
 
 struct patch_insn {
@@ -20,6 +21,8 @@ struct patch_insn {
 	atomic_t cpu_count;
 };
 
+int riscv_patch_in_stop_machine = false;
+
 #ifdef CONFIG_MMU
 /*
  * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
@@ -60,8 +63,15 @@ 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.
+	 *
+	 * We're currently using stop_machine() for ftrace & kprobes, and while
+	 * that ensures text_mutex is held before installing the mappings it
+	 * does not ensure text_mutex is held by the calling thread.  That's
+	 * safe but triggers a lockdep failure, so just elide it for that
+	 * specific case.
 	 */
-	lockdep_assert_held(&text_mutex);
+	if (!riscv_patch_in_stop_machine)
+		lockdep_assert_held(&text_mutex);
 
 	if (across_pages)
 		patch_map(addr + len, FIX_TEXT_POKE1);
@@ -125,6 +135,7 @@ NOKPROBE_SYMBOL(patch_text_cb);
 
 int patch_text(void *addr, u32 *insns, int ninsns)
 {
+	int ret;
 	struct patch_insn patch = {
 		.addr = addr,
 		.insns = insns,
@@ -132,7 +143,18 @@ int patch_text(void *addr, u32 *insns, int ninsns)
 		.cpu_count = ATOMIC_INIT(0),
 	};
 
-	return stop_machine_cpuslocked(patch_text_cb,
-				       &patch, cpu_online_mask);
+	/*
+	 * kprobes takes text_mutex, before calling patch_text(), but as we call
+	 * calls stop_machine(), the lockdep assertion in patch_insn_write()
+	 * gets confused by the context in which the lock is taken.
+	 * Instead, ensure the lock is held before calling stop_machine(), and
+	 * set riscv_patch_in_stop_machine to skip the check in
+	 * patch_insn_write().
+	 */
+	lockdep_assert_held(&text_mutex);
+	riscv_patch_in_stop_machine = true;
+	ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask);
+	riscv_patch_in_stop_machine = false;
+	return ret;
 }
 NOKPROBE_SYMBOL(patch_text);
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index f9a5a7c90ff0..64a9c093aef9 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -101,7 +101,7 @@ void notrace walk_stackframe(struct task_struct *task,
 	while (!kstack_end(ksp)) {
 		if (__kernel_text_address(pc) && unlikely(!fn(arg, pc)))
 			break;
-		pc = (*ksp++) - 0x4;
+		pc = READ_ONCE_NOCHECK(*ksp++) - 0x4;
 	}
 }