[PATCH v6 1/2] ftrace: disable preemption when recursion locked

[王贇 <yun.wang@linux.alibaba.com>]

As the documentation explained, ftrace_test_recursion_trylock()
and ftrace_test_recursion_unlock() were supposed to disable and
enable preemption properly, however currently this work is done
outside of the function, which could be missing by mistake.

And since the internal using of trace_test_and_set_recursion()
and trace_clear_recursion() also require preemption disabled, we
can just merge the logical.

This patch will make sure the preemption has been disabled when
trace_test_and_set_recursion() return bit >= 0, and
trace_clear_recursion() will enable the preemption if previously
enabled.

CC: Petr Mladek <pmladek@suse.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Miroslav Benes <mbenes@suse.cz>
Reported-by: Abaci <abaci@linux.alibaba.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
---
 arch/csky/kernel/probes/ftrace.c     |  2 --
 arch/parisc/kernel/ftrace.c          |  2 --
 arch/powerpc/kernel/kprobes-ftrace.c |  2 --
 arch/riscv/kernel/probes/ftrace.c    |  2 --
 arch/x86/kernel/kprobes/ftrace.c     |  2 --
 include/linux/trace_recursion.h      | 13 ++++++++++++-
 kernel/livepatch/patch.c             | 13 +++++++------
 kernel/trace/ftrace.c                | 15 +++++----------
 kernel/trace/trace_functions.c       |  5 -----
 9 files changed, 24 insertions(+), 32 deletions(-)

diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
index b388228..834cffc 100644
--- a/arch/csky/kernel/probes/ftrace.c
+++ b/arch/csky/kernel/probes/ftrace.c
@@ -17,7 +17,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		return;

 	regs = ftrace_get_regs(fregs);
-	preempt_disable_notrace();
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (!p) {
 		p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE));
@@ -57,7 +56,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		__this_cpu_write(current_kprobe, NULL);
 	}
 out:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c
index 7d14242..90c4345 100644
--- a/arch/parisc/kernel/ftrace.c
+++ b/arch/parisc/kernel/ftrace.c
@@ -210,7 +210,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		return;

 	regs = ftrace_get_regs(fregs);
-	preempt_disable_notrace();
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (unlikely(!p) || kprobe_disabled(p))
 		goto out;
@@ -239,7 +238,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	}
 	__this_cpu_write(current_kprobe, NULL);
 out:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c
index 7154d58..072ebe7 100644
--- a/arch/powerpc/kernel/kprobes-ftrace.c
+++ b/arch/powerpc/kernel/kprobes-ftrace.c
@@ -26,7 +26,6 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
 		return;

 	regs = ftrace_get_regs(fregs);
-	preempt_disable_notrace();
 	p = get_kprobe((kprobe_opcode_t *)nip);
 	if (unlikely(!p) || kprobe_disabled(p))
 		goto out;
@@ -61,7 +60,6 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
 		__this_cpu_write(current_kprobe, NULL);
 	}
 out:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c
index aab85a8..7142ec4 100644
--- a/arch/riscv/kernel/probes/ftrace.c
+++ b/arch/riscv/kernel/probes/ftrace.c
@@ -15,7 +15,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;

-	preempt_disable_notrace();
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (unlikely(!p) || kprobe_disabled(p))
 		goto out;
@@ -52,7 +51,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		__this_cpu_write(current_kprobe, NULL);
 	}
 out:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 596de2f..dd2ec14 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -25,7 +25,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;

-	preempt_disable_notrace();
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (unlikely(!p) || kprobe_disabled(p))
 		goto out;
@@ -59,7 +58,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		__this_cpu_write(current_kprobe, NULL);
 	}
 out:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index abe1a50..64c03ee 100644
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void)
 # define do_ftrace_record_recursion(ip, pip)	do { } while (0)
 #endif

+/*
+ * Preemption is promised to be disabled when return bit >= 0.
+ */
 static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
 							int start)
 {
@@ -162,11 +165,19 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
 	current->trace_recursion = val;
 	barrier();

+	preempt_disable_notrace();
+
 	return bit;
 }

+/*
+ * Preemption will be enabled (if it was previously enabled).
+ */
 static __always_inline void trace_clear_recursion(int bit)
 {
+	WARN_ON_ONCE(bit < 0);
+
+	preempt_enable_notrace();
 	barrier();
 	trace_recursion_clear(bit);
 }
@@ -178,7 +189,7 @@ static __always_inline void trace_clear_recursion(int bit)
  * tracing recursed in the same context (normal vs interrupt),
  *
  * Returns: -1 if a recursion happened.
- *           >= 0 if no recursion
+ *           >= 0 if no recursion.
  */
 static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
 							 unsigned long parent_ip)
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index e8029ae..b8d75fb 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -49,14 +49,16 @@ static void notrace klp_ftrace_handler(unsigned long ip,

 	ops = container_of(fops, struct klp_ops, fops);

+	/*
+	 *
+	 * The ftrace_test_recursion_trylock() will disable preemption,
+	 * which is required for the variant of synchronize_rcu() that is
+	 * used to allow patching functions where RCU is not watching.
+	 * See klp_synchronize_transition() for more details.
+	 */
 	bit = ftrace_test_recursion_trylock(ip, parent_ip);
 	if (WARN_ON_ONCE(bit < 0))
 		return;
-	/*
-	 * A variant of synchronize_rcu() is used to allow patching functions
-	 * where RCU is not watching, see klp_synchronize_transition().
-	 */
-	preempt_disable_notrace();

 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);
@@ -120,7 +122,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	klp_arch_set_pc(fregs, (unsigned long)func->new_func);

 unlock:
-	preempt_enable_notrace();
 	ftrace_test_recursion_unlock(bit);
 }

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b7be1df..7392bc7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7198,16 +7198,15 @@ void ftrace_reset_array_ops(struct trace_array *tr)
 	struct ftrace_ops *op;
 	int bit;

+	/*
+	 * The ftrace_test_and_set_recursion() will disable preemption,
+	 * which is required since some of the ops may be dynamically
+	 * allocated, they must be freed after a synchronize_rcu().
+	 */
 	bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START);
 	if (bit < 0)
 		return;

-	/*
-	 * Some of the ops may be dynamically allocated,
-	 * they must be freed after a synchronize_rcu().
-	 */
-	preempt_disable_notrace();
-
 	do_for_each_ftrace_op(op, ftrace_ops_list) {
 		/* Stub functions don't need to be called nor tested */
 		if (op->flags & FTRACE_OPS_FL_STUB)
@@ -7231,7 +7230,6 @@ void ftrace_reset_array_ops(struct trace_array *tr)
 		}
 	} while_for_each_ftrace_op(op);
 out:
-	preempt_enable_notrace();
 	trace_clear_recursion(bit);
 }

@@ -7279,12 +7277,9 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;

-	preempt_disable_notrace();
-
 	if (!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching())
 		op->func(ip, parent_ip, op, fregs);

-	preempt_enable_notrace();
 	trace_clear_recursion(bit);
 }
 NOKPROBE_SYMBOL(ftrace_ops_assist_func);
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 1f0e63f..9f1bfbe 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -186,7 +186,6 @@ static void function_trace_start(struct trace_array *tr)
 		return;

 	trace_ctx = tracing_gen_ctx();
-	preempt_disable_notrace();

 	cpu = smp_processor_id();
 	data = per_cpu_ptr(tr->array_buffer.data, cpu);
@@ -194,7 +193,6 @@ static void function_trace_start(struct trace_array *tr)
 		trace_function(tr, ip, parent_ip, trace_ctx);

 	ftrace_test_recursion_unlock(bit);
-	preempt_enable_notrace();
 }

 #ifdef CONFIG_UNWINDER_ORC
@@ -298,8 +296,6 @@ static inline void process_repeats(struct trace_array *tr,
 	if (bit < 0)
 		return;

-	preempt_disable_notrace();
-
 	cpu = smp_processor_id();
 	data = per_cpu_ptr(tr->array_buffer.data, cpu);
 	if (atomic_read(&data->disabled))
@@ -324,7 +320,6 @@ static inline void process_repeats(struct trace_array *tr,

 out:
 	ftrace_test_recursion_unlock(bit);
-	preempt_enable_notrace();
 }

 static void
-- 
1.8.3.1