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Fix arc_adapt() spinning in iterate_supers_type()

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The iterate_supers_type() function which was introduced in the
3.0 kernel was supposed to provide a safe way to call an arbitrary
function on all super blocks of a specific type.  Unfortunately,
because a list_head was used a bug was introduced which made it
possible for iterate_supers_type() to get stuck spinning on a
super block which was just deactivated.

This can occur because when the list head is removed from the
fs_supers list it is reinitialized to point to itself.  If the
iterate_supers_type() function happened to be processing the
removed list_head it will get stuck spinning on that list_head.

The bug was fixed in the 3.3 kernel by converting the list_head
to an hlist_node.  However, to resolve the issue for existing
3.0 - 3.2 kernels we detect when a list_head is used.  Then to
prevent the spinning from occurring the .next pointer is set to
the fs_supers list_head which ensures the iterate_supers_type()
function will always terminate.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1045
Closes #861
Closes #790
This commit is contained in:
Brian Behlendorf 2013-07-15 13:37:51 -07:00
parent c9ada6d5a0
commit dba1d70566
3 changed files with 44 additions and 0 deletions
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39
config/kernel-shrink.m4
View File

@ -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([

1
config/kernel.m4
View File

@ -72,6 +72,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
ZFS_AC_KERNEL_CALLBACK_SECURITY_INODE_INIT_SECURITY
ZFS_AC_KERNEL_MOUNT_NODEV
ZFS_AC_KERNEL_SHRINK
ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD
ZFS_AC_KERNEL_S_D_OP
ZFS_AC_KERNEL_BDI
ZFS_AC_KERNEL_BDI_SETUP_AND_REGISTER

4
module/zfs/zpl_super.c
View File

@ -240,6 +240,10 @@ zpl_kill_sb(struct super_block *sb)
{
zfs_preumount(sb);
kill_anon_super(sb);
#ifdef HAVE_S_INSTANCES_LIST_HEAD
sb->s_instances.next = &(zpl_fs_type.fs_supers);
#endif /* HAVE_S_INSTANCES_LIST_HEAD */
}
#ifdef HAVE_SHRINK