Description:
------------
ThreadSanitizer has detected a data race in php_xsl.c.

The function xsltSetGenericErrorFunc is not thread safe, yet it can be accessed 
concurrently by separate threads from the request INIT & SHUTDOWN handlers in the 
xslt extension.


/* {{{ PHP_RINIT_FUNCTION
 */
PHP_RINIT_FUNCTION(xsl)
{
	xsltSetGenericErrorFunc(NULL, php_libxml_error_handler);
	return SUCCESS;
}
/* }}} */

/* {{{ PHP_RSHUTDOWN_FUNCTION
 */
PHP_RSHUTDOWN_FUNCTION(xsl)
{
	xsltSetGenericErrorFunc(NULL, NULL);
	return SUCCESS;
}

xsltSetGenericErrorFunc uses two global variables to record state, with no 
protection against concurrent access.


from xsltutils.c

xmlGenericErrorFunc xsltGenericError = xsltGenericErrorDefaultFunc;
void *xsltGenericErrorContext = NULL;


/**
 * xsltSetGenericErrorFunc:
 * @ctx:  the new error handling context
 * @handler:  the new handler function
 *
 * Function to reset the handler and the error context for out of
 * context error messages.
 * This simply means that @handler will be called for subsequent
 * error messages while not parsing nor validating. And @ctx will
 * be passed as first argument to @handler
 * One can simply force messages to be emitted to another FILE * than
 * stderr by setting @ctx to this file handle and @handler to NULL.
 */
void
xsltSetGenericErrorFunc(void *ctx, xmlGenericErrorFunc handler) {
    xsltGenericErrorContext = ctx;
    if (handler != NULL)
	xsltGenericError = handler;
    else
	xsltGenericError = xsltGenericErrorDefaultFunc;
}

Calling xsltSetGenericErrorFunc from the module initializer should solve this 
problem.

Test script:
---------------
build PHP with --enable-maintainer-zts.

Execute concurrent requests.