[PATCH v5 0/2] fix & prevent the missing preemption disabling

[PATCH v5 0/2] fix & prevent the missing preemption disabling

[王贇]

The testing show that perf_ftrace_function_call() are using smp_processor_id()
with preemption enabled, all the checking on CPU could be wrong after preemption.

As Peter point out, the section between ftrace_test_recursion_trylock/unlock()
pair require the preemption to be disabled as 'Documentation/trace/ftrace-uses.rst'
explained, but currently the work is done outside of the helpers.

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

Patch 1/2 will make sure preemption disabled when recursion lock succeed,
patch 2/2 will do smp_processor_id() checking after trylock() to address the
issue.

v1: https://lore.kernel.org/all/8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com/
v2: https://lore.kernel.org/all/b1d7fe43-ce84-0ed7-32f7-ea1d12d0b716@linux.alibaba.com/
v3: https://lore.kernel.org/all/609b565a-ed6e-a1da-f025-166691b5d994@linux.alibaba.com/
V4: https://lore.kernel.org/all/32a36348-69ee-6464-390c-3a8d6e9d2b53@linux.alibaba.com/

Michael Wang (2):
  ftrace: disable preemption when recursion locked
  ftrace: do CPU checking after preemption disabled

 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      | 11 ++++++++++-
 kernel/livepatch/patch.c             | 13 +++++++------
 kernel/trace/ftrace.c                | 15 +++++----------
 kernel/trace/trace_event_perf.c      |  6 +++---
 kernel/trace/trace_functions.c       |  5 -----
 10 files changed, 25 insertions(+), 35 deletions(-)

-- 
1.8.3.1

[PATCH v5 1/2] ftrace: disable preemption when recursion locked

[王贇]

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      | 11 ++++++++++-
 kernel/livepatch/patch.c             | 13 +++++++------
 kernel/trace/ftrace.c                | 15 +++++----------
 kernel/trace/trace_functions.c       |  5 -----
 9 files changed, 22 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..2bc1522 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 +165,17 @@ 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)
 {
+	preempt_enable_notrace();
 	barrier();
 	trace_recursion_clear(bit);
 }
@@ -178,7 +187,7 @@ 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

[PATCH v5 2/2] ftrace: do CPU checking after preemption disabled

[王贇]

With CONFIG_DEBUG_PREEMPT we observed reports like:

  BUG: using smp_processor_id() in preemptible
  caller is perf_ftrace_function_call+0x6f/0x2e0
  CPU: 1 PID: 680 Comm: a.out Not tainted
  Call Trace:
   <TASK>
   dump_stack_lvl+0x8d/0xcf
   check_preemption_disabled+0x104/0x110
   ? optimize_nops.isra.7+0x230/0x230
   ? text_poke_bp_batch+0x9f/0x310
   perf_ftrace_function_call+0x6f/0x2e0
   ...
   __text_poke+0x5/0x620
   text_poke_bp_batch+0x9f/0x310

This telling us the CPU could be changed after task is preempted, and
the checking on CPU before preemption will be invalid.

Since now ftrace_test_recursion_trylock() will help to disable the
preemption, this patch just do the checking after trylock() to address
the issue.

CC: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Abaci <abaci@linux.alibaba.com>
Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
---
 kernel/trace/trace_event_perf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 6aed10e..fba8cb7 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -441,13 +441,13 @@ void perf_trace_buf_update(void *record, u16 type)
 	if (!rcu_is_watching())
 		return;

-	if ((unsigned long)ops->private != smp_processor_id())
-		return;
-
 	bit = ftrace_test_recursion_trylock(ip, parent_ip);
 	if (bit < 0)
 		return;

+	if ((unsigned long)ops->private != smp_processor_id())
+		goto out;
+
 	event = container_of(ops, struct perf_event, ftrace_ops);

 	/*
-- 
1.8.3.1

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[Miroslav Benes]

Hi,

> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index abe1a50..2bc1522 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 +165,17 @@ 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)
>  {
> +	preempt_enable_notrace();
>  	barrier();
>  	trace_recursion_clear(bit);
>  }

The two comments should be updated too since Steven removed the "bit == 0" 
trick.

> @@ -178,7 +187,7 @@ 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)

And this change would not be correct now.

Regards
Miroslav

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[王贇]

Hi, Miroslav

On 2021/10/26 下午5:35, Miroslav Benes wrote:
> Hi,
> 
>> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
>> index abe1a50..2bc1522 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 +165,17 @@ 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)
>>  {
>> +	preempt_enable_notrace();
>>  	barrier();
>>  	trace_recursion_clear(bit);
>>  }
> 
> The two comments should be updated too since Steven removed the "bit == 0" 
> trick.

Could you please give more hint on how will it be correct?

I get the point that bit will no longer be 0, there are only -1 or > 0 now
so trace_test_and_set_recursion() will disable preemption on bit > 0 and
trace_clear_recursion() will enabled it since it should only be called when
bit > 0 (I remember we could use a WARN_ON here now :-P).

> 
>> @@ -178,7 +187,7 @@ 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)
> 
> And this change would not be correct now.

I thought it will no longer return 0 so I change it to > 0, isn't that correct?

Regards,
Michael Wang

> 
> Regards
> Miroslav
> 

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[Steven Rostedt]

On Tue, 26 Oct 2021 17:48:10 +0800
王贇 <yun.wang@linux.alibaba.com> wrote:

> > The two comments should be updated too since Steven removed the "bit == 0" 
> > trick.  
> 
> Could you please give more hint on how will it be correct?
> 
> I get the point that bit will no longer be 0, there are only -1 or > 0 now
> so trace_test_and_set_recursion() will disable preemption on bit > 0 and
> trace_clear_recursion() will enabled it since it should only be called when
> bit > 0 (I remember we could use a WARN_ON here now :-P).
> 
> >   
> >> @@ -178,7 +187,7 @@ 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)  
> > 
> > And this change would not be correct now.  
> 
> I thought it will no longer return 0 so I change it to > 0, isn't that correct?

No it is not. I removed the bit + 1 return value, which means it returns the
actual bit now. Which is 0 or more.

-- Steve

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[王贇]

On 2021/10/26 下午8:01, Steven Rostedt wrote:
> On Tue, 26 Oct 2021 17:48:10 +0800
> 王贇 <yun.wang@linux.alibaba.com> wrote:
> 
>>> The two comments should be updated too since Steven removed the "bit == 0" 
>>> trick.  
>>
>> Could you please give more hint on how will it be correct?
>>
>> I get the point that bit will no longer be 0, there are only -1 or > 0 now
>> so trace_test_and_set_recursion() will disable preemption on bit > 0 and
>> trace_clear_recursion() will enabled it since it should only be called when
>> bit > 0 (I remember we could use a WARN_ON here now :-P).
>>
>>>   
>>>> @@ -178,7 +187,7 @@ 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)  
>>>
>>> And this change would not be correct now.  
>>
>> I thought it will no longer return 0 so I change it to > 0, isn't that correct?
> 
> No it is not. I removed the bit + 1 return value, which means it returns the
> actual bit now. Which is 0 or more.

Ah, the return is bit not val, I must be drunk...

My apologize for the stupid comments... I'll send a v6 for this patch
only to fix that, please let me know if this is not a good way to fix
few lines of comments.

Regards,
Michael Wang

> 
> -- Steve
> 

[PATCH v6] ftrace: disable preemption when recursion locked

[王贇]

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

Re: [PATCH v6] ftrace: disable preemption when recursion locked

[王贇]

Hi, Steven, Miroslav

Should have fixed the comments about bit value, besides, add
a warn in trace_clear_recursion() to make sure the bit < 0
abusing case will get notified.

Please let me know if there are any other issues :-)

Regards,
Michael Wang

On 2021/10/27 上午10:11, 王贇 wrote:
> 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
> 

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[Steven Rostedt]

On Wed, 27 Oct 2021 09:54:13 +0800
王贇 <yun.wang@linux.alibaba.com> wrote:

> My apologize for the stupid comments... I'll send a v6 for this patch
> only to fix that, please let me know if this is not a good way to fix
> few lines of comments.

Actually, please resend both patches, as a new patch set, on its own thread.

Just replying here won't trigger my patchwork scripts.

And also, if you don't include the other patch, the scripts will drop
it.

Thanks,

-- Steve

Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

[王贇]

On 2021/10/27 上午10:26, Steven Rostedt wrote:
> On Wed, 27 Oct 2021 09:54:13 +0800
> 王贇 <yun.wang@linux.alibaba.com> wrote:
> 
>> My apologize for the stupid comments... I'll send a v6 for this patch
>> only to fix that, please let me know if this is not a good way to fix
>> few lines of comments.
> 
> Actually, please resend both patches, as a new patch set, on its own thread.
> 
> Just replying here won't trigger my patchwork scripts.
> 
> And also, if you don't include the other patch, the scripts will drop
> it.

Got it~

Regards,
Michael Wang

> 
> Thanks,
> 
> -- Steve
>