Fix arc_adapt() spinning in iterate_supers_type()

[zfs.git] / config / kernel-shrink.m4

diff --git a/config/kernel-shrink.m4 b/config/kernel-shrink.m4
index 479fb3a..1c211ed 100644 (file)
--- a/config/kernel-shrink.m4
+++ b/config/kernel-shrink.m4
@@ -28,6 +28,45 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINK], [
        ])
 ])
 
+dnl #
+dnl # 3.3 API change
+dnl # The super_block structure was changed to use an hlist_node instead
+dnl # of a list_head for the .s_instance linkage.
+dnl #
+dnl # This was done in part to resolve a race in the iterate_supers_type()
+dnl # function which was introduced in Linux 3.0 kernel.  The iterator
+dnl # was supposed to provide a safe way to call an arbitrary function on
+dnl # all super blocks of a specific type.  Unfortunately, because a
+dnl # list_head was used it was possible for iterate_supers_type() to
+dnl # get stuck spinning a super block which was just deactivated.
+dnl #
+dnl # This can occur because when the list head is removed from the
+dnl # fs_supers list it is reinitialized to point to itself.  If the
+dnl # iterate_supers_type() function happened to be processing the
+dnl # removed list_head it will get stuck spinning on that list_head.
+dnl #
+dnl # To resolve the issue for existing 3.0 - 3.2 kernels we detect when
+dnl # a list_head is used.  Then to prevent the spinning from occurring
+dnl # the .next pointer is set to the fs_supers list_head which ensures
+dnl # the iterate_supers_type() function will always terminate.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD], [
+       AC_MSG_CHECKING([whether super_block has s_instances list_head])
+       ZFS_LINUX_TRY_COMPILE([
+               #include <linux/fs.h>
+       ],[
+               struct super_block sb __attribute__ ((unused));
+
+               INIT_LIST_HEAD(&sb.s_instances);
+       ],[
+               AC_MSG_RESULT(yes)
+               AC_DEFINE(HAVE_S_INSTANCES_LIST_HEAD, 1,
+                   [struct super_block has s_instances list_head])
+       ],[
+               AC_MSG_RESULT(no)
+       ])
+])
+
 AC_DEFUN([ZFS_AC_KERNEL_NR_CACHED_OBJECTS], [
        AC_MSG_CHECKING([whether sops->nr_cached_objects() exists])
        ZFS_LINUX_TRY_COMPILE([