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authorJan Kara <jack@suse.cz>2017-03-14 14:31:02 +0300
committerJan Kara <jack@suse.cz>2017-04-10 18:37:34 +0300
commit9dd813c15b2c101168808d4f5941a29985758973 (patch)
tree62646b8b8e4335b9d311bdcd3224d12308961c20 /include/linux/fsnotify_backend.h
parentc1f33073ac1b33510e956de7181438515e438db0 (diff)
downloadlinux-9dd813c15b2c101168808d4f5941a29985758973.tar.xz
fsnotify: Move mark list head from object into dedicated structure
Currently notification marks are attached to object (inode or vfsmnt) by a hlist_head in the object. The list is also protected by a spinlock in the object. So while there is any mark attached to the list of marks, the object must be pinned in memory (and thus e.g. last iput() deleting inode cannot happen). Also for list iteration in fsnotify() to work, we must hold fsnotify_mark_srcu lock so that mark itself and mark->obj_list.next cannot get freed. Thus we are required to wait for response to fanotify events from userspace process with fsnotify_mark_srcu lock held. That causes issues when userspace process is buggy and does not reply to some event - basically the whole notification subsystem gets eventually stuck. So to be able to drop fsnotify_mark_srcu lock while waiting for response, we have to pin the mark in memory and make sure it stays in the object list (as removing the mark waiting for response could lead to lost notification events for groups later in the list). However we don't want inode reclaim to block on such mark as that would lead to system just locking up elsewhere. This commit is the first in the series that paves way towards solving these conflicting lifetime needs. Instead of anchoring the list of marks directly in the object, we anchor it in a dedicated structure (fsnotify_mark_connector) and just point to that structure from the object. The following commits will also add spinlock protecting the list and object pointer to the structure. Reviewed-by: Miklos Szeredi <mszeredi@redhat.com> Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'include/linux/fsnotify_backend.h')
-rw-r--r--include/linux/fsnotify_backend.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index e6e689b5569e..8b63085f8855 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -195,6 +195,15 @@ struct fsnotify_group {
#define FSNOTIFY_EVENT_INODE 2
/*
+ * Inode / vfsmount point to this structure which tracks all marks attached to
+ * the inode / vfsmount. The structure is freed only when inode / vfsmount gets
+ * freed.
+ */
+struct fsnotify_mark_connector {
+ struct hlist_head list;
+};
+
+/*
* A mark is simply an object attached to an in core inode which allows an
* fsnotify listener to indicate they are either no longer interested in events
* of a type matching mask or only interested in those events.
@@ -346,6 +355,7 @@ extern void fsnotify_clear_vfsmount_marks_by_group(struct fsnotify_group *group)
extern void fsnotify_clear_inode_marks_by_group(struct fsnotify_group *group);
/* run all the marks in a group, and clear all of the marks where mark->flags & flags is true*/
extern void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags);
+extern void fsnotify_connector_free(struct fsnotify_mark_connector **connp);
extern void fsnotify_get_mark(struct fsnotify_mark *mark);
extern void fsnotify_put_mark(struct fsnotify_mark *mark);
extern void fsnotify_unmount_inodes(struct super_block *sb);