Commit 3d62ab32 authored by Luo Gengkun's avatar Luo Gengkun Committed by Steven Rostedt (Google)
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tracing: Fix tracing_marker may trigger page fault during preempt_disable 

Both tracing_mark_write and tracing_mark_raw_write call
__copy_from_user_inatomic during preempt_disable. But in some case,
__copy_from_user_inatomic may trigger page fault, and will call schedule()
subtly. And if a task is migrated to other cpu, the following warning will
be trigger:
        if (RB_WARN_ON(cpu_buffer,
                       !local_read(&cpu_buffer->committing)))

An example can illustrate this issue:

process flow						CPU
---------------------------------------------------------------------

tracing_mark_raw_write():				cpu:0
   ...
   ring_buffer_lock_reserve():				cpu:0
      ...
      cpu = raw_smp_processor_id()			cpu:0
      cpu_buffer = buffer->buffers[cpu]			cpu:0
      ...
   ...
   __copy_from_user_inatomic():				cpu:0
      ...
      # page fault
      do_mem_abort():					cpu:0
         ...
         # Call schedule
         schedule()					cpu:0
	 ...
   # the task schedule to cpu1
   __buffer_unlock_commit():				cpu:1
      ...
      ring_buffer_unlock_commit():			cpu:1
	 ...
	 cpu = raw_smp_processor_id()			cpu:1
	 cpu_buffer = buffer->buffers[cpu]		cpu:1

As shown above, the process will acquire cpuid twice and the return values
are not the same.

To fix this problem using copy_from_user_nofault instead of
__copy_from_user_inatomic, as the former performs 'access_ok' before
copying.

Link: https://lore.kernel.org/20250819105152.2766363-1-luogengkun@huaweicloud.com


Fixes: 656c7f0d ("tracing: Replace kmap with copy_from_user() in trace_marker writing")
Signed-off-by: default avatarLuo Gengkun <luogengkun@huaweicloud.com>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 81ac6332

kernel/trace/trace.c

+2 −2
Original line number Diff line number Diff line
@@ -7209,7 +7209,7 @@ static ssize_t write_marker_to_buffer(struct trace_array *tr, const char __user 
	entry = ring_buffer_event_data(event);

	entry->ip = ip;



	len = __copy_from_user_inatomic(&entry->buf, ubuf, cnt);

	len = copy_from_user_nofault(&entry->buf, ubuf, cnt);

	if (len) {

		memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE);

		cnt = FAULTED_SIZE;
@@ -7306,7 +7306,7 @@ static ssize_t write_raw_marker_to_buffer(struct trace_array *tr, 


	entry = ring_buffer_event_data(event);



	len = __copy_from_user_inatomic(&entry->id, ubuf, cnt);

	len = copy_from_user_nofault(&entry->id, ubuf, cnt);

	if (len) {

		entry->id = -1;

		memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE);