tracing: Move mutex to protect against resetting of seq data

The iter->seq can be reset outside the protection of the mutex. So can
reading of user data. Move the mutex up to the beginning of the function.

Fixes: d7350c3f45694 ("tracing/core: make the read callbacks reentrants")
Cc: stable@vger.kernel.org # 2.6.30+
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

path: root/error.c

#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <signal.h>

void error_exit(char *format, ...)
{
	char buffer[4096];
	va_list ap;

	va_start(ap, format);
	vsnprintf(buffer, sizeof(buffer), format, ap);
	va_end(ap);

	fprintf(stderr, "%s: errno=%d (if applicable)\n", buffer, errno);

	exit(EXIT_FAILURE);
}