MDEV-26674 workaround for mariadb-backup

This is follow-up to commit 1193a793c4.
We will set innodb_use_native_aio=OFF by default also in mariadb-backup
when running on a potentially affected kernel.

extra/mariabackup/xtrabackup.cc

@@ -1392,6 +1392,11 @@ uint xb_client_options_count = array_elements(xb_client_options);
 static const char *dbug_option;
 #endif
 
+#ifdef HAVE_URING
+extern const char *io_uring_may_be_unsafe;
+bool innodb_use_native_aio_default();
+#endif
+
 struct my_option xb_server_options[] =
 {
   {"datadir", 'h', "Path to the database root.", (G_PTR*) &mysql_data_home,
@@ -1508,7 +1513,12 @@ struct my_option xb_server_options[] =
    "Use native AIO if supported on this platform.",
    (G_PTR*) &srv_use_native_aio,
    (G_PTR*) &srv_use_native_aio, 0, GET_BOOL, NO_ARG,
-   TRUE, 0, 0, 0, 0, 0},
+#ifdef HAVE_URING
+   innodb_use_native_aio_default(),
+#else
+   TRUE,
+#endif
+   0, 0, 0, 0, 0},
   {"innodb_page_size", OPT_INNODB_PAGE_SIZE,
    "The universal page size of the database.",
    (G_PTR*) &innobase_page_size, (G_PTR*) &innobase_page_size, 0,
@@ -2071,8 +2081,12 @@ static bool innodb_init_param()
 		msg("InnoDB: Using Linux native AIO");
 	}
 #elif defined(HAVE_URING)
-
-	if (srv_use_native_aio) {
+	if (!srv_use_native_aio) {
+	} else if (io_uring_may_be_unsafe) {
+		msg("InnoDB: Using liburing on this kernel %s may cause hangs;"
+		    " see https://jira.mariadb.org/browse/MDEV-26674",
+		    io_uring_may_be_unsafe);
+	} else {
 		msg("InnoDB: Using liburing");
 	}
 #else

storage/innobase/handler/ha_innodb.cc

@@ -152,7 +152,7 @@ void close_thread_tables(THD* thd);
 
 #ifdef HAVE_URING
 /** The Linux kernel version if io_uring() is considered unsafe */
-static const char *io_uring_may_be_unsafe;
+const char *io_uring_may_be_unsafe;
 #endif
 
 #define INSIDE_HA_INNOBASE_CC
@@ -19390,9 +19390,10 @@ static MYSQL_SYSVAR_STR(version, innodb_version_str,
 #ifdef HAVE_URING
 # include <sys/utsname.h>
 static utsname uname_for_io_uring;
+#else
+static
 #endif
-
-static bool innodb_use_native_aio_default()
+bool innodb_use_native_aio_default()
 {
 #ifdef HAVE_URING
   utsname &u= uname_for_io_uring;