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dba1d70566
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
112 lines
3.2 KiB
Plaintext
112 lines
3.2 KiB
Plaintext
dnl #
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dnl # 3.1 API change
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dnl # The super_block structure now stores a per-filesystem shrinker.
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dnl # This interface is preferable because it can be used to specifically
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dnl # target only the zfs filesystem for pruning.
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dnl #
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AC_DEFUN([ZFS_AC_KERNEL_SHRINK], [
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AC_MSG_CHECKING([whether super_block has s_shrink])
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ZFS_LINUX_TRY_COMPILE([
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#include <linux/fs.h>
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int shrink(struct shrinker *s, struct shrink_control *sc)
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{ return 0; }
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static const struct super_block
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sb __attribute__ ((unused)) = {
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.s_shrink.shrink = shrink,
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.s_shrink.seeks = DEFAULT_SEEKS,
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.s_shrink.batch = 0,
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};
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],[
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],[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_SHRINK, 1, [struct super_block has s_shrink])
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],[
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AC_MSG_RESULT(no)
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])
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])
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dnl #
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dnl # 3.3 API change
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dnl # The super_block structure was changed to use an hlist_node instead
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dnl # of a list_head for the .s_instance linkage.
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dnl #
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dnl # This was done in part to resolve a race in the iterate_supers_type()
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dnl # function which was introduced in Linux 3.0 kernel. The iterator
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dnl # was supposed to provide a safe way to call an arbitrary function on
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dnl # all super blocks of a specific type. Unfortunately, because a
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dnl # list_head was used it was possible for iterate_supers_type() to
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dnl # get stuck spinning a super block which was just deactivated.
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dnl #
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dnl # This can occur because when the list head is removed from the
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dnl # fs_supers list it is reinitialized to point to itself. If the
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dnl # iterate_supers_type() function happened to be processing the
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dnl # removed list_head it will get stuck spinning on that list_head.
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dnl #
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dnl # To resolve the issue for existing 3.0 - 3.2 kernels we detect when
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dnl # a list_head is used. Then to prevent the spinning from occurring
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dnl # the .next pointer is set to the fs_supers list_head which ensures
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dnl # the iterate_supers_type() function will always terminate.
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dnl #
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AC_DEFUN([ZFS_AC_KERNEL_S_INSTANCES_LIST_HEAD], [
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AC_MSG_CHECKING([whether super_block has s_instances list_head])
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ZFS_LINUX_TRY_COMPILE([
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#include <linux/fs.h>
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],[
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struct super_block sb __attribute__ ((unused));
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INIT_LIST_HEAD(&sb.s_instances);
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],[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_S_INSTANCES_LIST_HEAD, 1,
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[struct super_block has s_instances list_head])
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],[
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AC_MSG_RESULT(no)
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])
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])
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AC_DEFUN([ZFS_AC_KERNEL_NR_CACHED_OBJECTS], [
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AC_MSG_CHECKING([whether sops->nr_cached_objects() exists])
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ZFS_LINUX_TRY_COMPILE([
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#include <linux/fs.h>
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int nr_cached_objects(struct super_block *sb) { return 0; }
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static const struct super_operations
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sops __attribute__ ((unused)) = {
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.nr_cached_objects = nr_cached_objects,
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};
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],[
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],[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_NR_CACHED_OBJECTS, 1,
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[sops->nr_cached_objects() exists])
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],[
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AC_MSG_RESULT(no)
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])
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])
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AC_DEFUN([ZFS_AC_KERNEL_FREE_CACHED_OBJECTS], [
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AC_MSG_CHECKING([whether sops->free_cached_objects() exists])
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ZFS_LINUX_TRY_COMPILE([
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#include <linux/fs.h>
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void free_cached_objects(struct super_block *sb, int x)
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{ return; }
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static const struct super_operations
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sops __attribute__ ((unused)) = {
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.free_cached_objects = free_cached_objects,
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};
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],[
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],[
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_FREE_CACHED_OBJECTS, 1,
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[sops->free_cached_objects() exists])
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],[
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AC_MSG_RESULT(no)
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])
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])
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