MDEV-26674: Set innodb_use_native_aio=OFF when using io_uring on a po…

…tentially affected kernel

We have observed hangs of the io_uring subsystem when using a
Linux kernel newer than 5.10. Also 5.15-rc6 is affected by this.

The exact cause of the hangs has not been diagnosed yet.
As a safety measure, we will disable innodb_use_native_aio by default
when the server has been configured with io_uring and the kernel
version is between 5.11 and 5.15.

If the start-up parameter innodb_use_native_aio=ON is set, then
we will issue a warning to the server error log.

storage/innobase/handler/ha_innodb.cc

@@ -150,6 +150,11 @@ void close_thread_tables(THD* thd);
 #include "wsrep_sst.h"
 #endif /* WITH_WSREP */
 
+#ifdef HAVE_URING
+/** The Linux kernel version if io_uring() is considered unsafe */
+static const char *io_uring_may_be_unsafe;
+#endif
+
 #define INSIDE_HA_INNOBASE_CC
 
 #define EQ_CURRENT_THD(thd) ((thd) == current_thd)
@@ -4046,6 +4051,14 @@ static int innodb_init_params()
 	cases, we ignore the setting of innodb_use_native_aio. */
 	srv_use_native_aio = FALSE;
 #endif
+#ifdef HAVE_URING
+	if (srv_use_native_aio && io_uring_may_be_unsafe) {
+		sql_print_warning("innodb_use_native_aio may cause "
+				  "hangs with this kernel %s; see "
+				  "https://jira.mariadb.org/browse/MDEV-26674",
+				  io_uring_may_be_unsafe);
+	}
+#endif
 
 #ifndef _WIN32
 	ut_ad(srv_file_flush_method <= SRV_O_DIRECT_NO_FSYNC);
@@ -19393,10 +19406,29 @@ static MYSQL_SYSVAR_STR(version, innodb_version_str,
   PLUGIN_VAR_NOCMDOPT | PLUGIN_VAR_READONLY,
   "InnoDB version", NULL, NULL, INNODB_VERSION_STR);
 
+#ifdef HAVE_URING
+# include <sys/utsname.h>
+static utsname uname_for_io_uring;
+#endif
+
+static bool innodb_use_native_aio_default()
+{
+#ifdef HAVE_URING
+  utsname &u= uname_for_io_uring;
+  if (!uname(&u) && u.release[0] == '5' && u.release[1] == '.' &&
+      u.release[2] == '1' && u.release[3] > '0' && u.release[3] < '6')
+  {
+    io_uring_may_be_unsafe= u.release;
+    return false; /* working around io_uring hangs (MDEV-26674) */
+  }
+#endif
+  return true;
+}
+
 static MYSQL_SYSVAR_BOOL(use_native_aio, srv_use_native_aio,
   PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
   "Use native AIO if supported on this platform.",
-  NULL, NULL, TRUE);
+  NULL, NULL, innodb_use_native_aio_default());
 
 #ifdef HAVE_LIBNUMA
 static MYSQL_SYSVAR_BOOL(numa_interleave, srv_numa_interleave,