Re: [PATCH v2 1/3] tracing: Have futex syscall trace event show specific user data

[Steven Rostedt <rostedt@kernel.org>]

On Wed, 11 Mar 2026 18:03:25 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"  __print_symbolic(REC->op & 0x%x, ", FUTEX_CMD_MASK);
> > +
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAIT\"}, ", FUTEX_WAIT);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAKE\"}, ", FUTEX_WAKE);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_FD\"}, ", FUTEX_FD);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_REQUEUE\"}, ", FUTEX_REQUEUE);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_CMP_REQUEUE\"}, ", FUTEX_CMP_REQUEUE);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAKE_OP\"}, ", FUTEX_WAKE_OP);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_LOCK_PI\"}, ", FUTEX_LOCK_PI);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_UNLOCK_PI\"}, ", FUTEX_UNLOCK_PI);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_TRYLOCK_PI\"}, ", FUTEX_TRYLOCK_PI);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAIT_BITSET\"}, ", FUTEX_WAIT_BITSET);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAKE_BITSET\"}, ", FUTEX_WAKE_BITSET);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_WAIT_REQUEUE_PI\"}, ", FUTEX_WAIT_REQUEUE_PI);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_CMP_REQUEUE_PI\"}, ", FUTEX_CMP_REQUEUE_PI);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			"{%d, \"FUTEX_LOCK_PI2\"}),", FUTEX_LOCK_PI2);  
> 
> Hmm can we share __futex_cmds[] with kernel/futex/syscalls.c?
> Then these could be
> 
> for (i = 0; i <= FUTEX_LOCK_PI2; i++)
> 	pos += snprintf(buf + pos, LEN_OR_ZERO,
> 			"{%d, \"%s\"}%s", i, __futex_cmds[i],
> 			i == FUTEX_LOCK_PI2 ? ")," : ", ");

Hmm, I created the above *before* creating the __futex_cmds. But yes, that
makes sense. Thanks for the suggestion.


> 
> 
> > +
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			" (REC->op & %d) ? \"|FUTEX_PRIVATE_FLAG\" : \"\",",
> > +			FUTEX_PRIVATE_FLAG);
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			" (REC->op & %d) ? \"|FUTEX_CLOCK_REALTIME\" : \"\",",
> > +			FUTEX_CLOCK_REALTIME);
> > +
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			" REC->val, REC->utime,");
> > +
> > +	pos += snprintf(buf + pos, LEN_OR_ZERO,
> > +			" REC->uaddr, REC->val3");
> > +	return pos;
> > +}
> > +
> >  static int __init
> >  __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
> >  {  
> [...]
> > @@ -689,6 +799,48 @@ static int syscall_copy_user_array(char *buf, const char __user *ptr,
> >  	return 0;
> >  }
> >  
> > +static int
> > +syscall_get_futex(unsigned long *args, char **buffer, int *size, int buf_size)
> > +{
> > +	struct syscall_user_buffer *sbuf;
> > +	const char __user *ptr;
> > +	char *buf;
> > +
> > +	/* buf_size of zero means user doesn't want user space read */
> > +	if (!buf_size)
> > +		return -1;
> > +
> > +	/* If the syscall_buffer is NULL, tracing is being shutdown */
> > +	sbuf = READ_ONCE(syscall_buffer);
> > +	if (!sbuf)
> > +		return -1;
> > +
> > +	ptr = (char __user *)args[0];
> > +
> > +	*buffer = trace_user_fault_read(&sbuf->buf, ptr, 4, NULL, NULL);
> > +	if (!*buffer)
> > +		return -1;
> > +
> > +	/* Add room for the value */
> > +	*size += 4;
> > +
> > +	buf = *buffer;  
> 
> As kernel test bot says, this does nothing. (*buffer is already assigned)
> 

Oops, I think this was a cut-and-paste error :-p

-- Steve