linux-kernel - [PATCH v2 1/7] fsnotify: clean up fsnotify_prepare/finish_user

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Message-Id: <1508920899-8115-2-git-send-email-mszeredi@redhat.com>
Date:   Wed, 25 Oct 2017 10:41:33 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        Xiong Zhou <xzhou@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/7] fsnotify: clean up fsnotify_prepare/finish_user_wait()

This patch doesn't actually fix any bug, just paves the way for fixing mark
and group pinning.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Cc: <stable@...r.kernel.org> # v4.12
---
 fs/notify/mark.c | 89 ++++++++++++++++++++++++++------------------------------
 1 file changed, 41 insertions(+), 48 deletions(-)

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 9991f8826734..982527ce6a58 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -109,16 +109,6 @@ void fsnotify_get_mark(struct fsnotify_mark *mark)
 	atomic_inc(&mark->refcnt);
 }
 
-/*
- * Get mark reference when we found the mark via lockless traversal of object
- * list. Mark can be already removed from the list by now and on its way to be
- * destroyed once SRCU period ends.
- */
-static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
-{
-	return atomic_inc_not_zero(&mark->refcnt);
-}
-
 static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 {
 	u32 new_mask = 0;
@@ -256,32 +246,56 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
 			   FSNOTIFY_REAPER_DELAY);
 }
 
-bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
+/*
+ * Get mark reference when we found the mark via lockless traversal of object
+ * list. Mark can be already removed from the list by now and on its way to be
+ * destroyed once SRCU period ends.
+ */
+static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
 {
 	struct fsnotify_group *group;
 
-	if (WARN_ON_ONCE(!iter_info->inode_mark && !iter_info->vfsmount_mark))
-		return false;
-
-	if (iter_info->inode_mark)
-		group = iter_info->inode_mark->group;
-	else
-		group = iter_info->vfsmount_mark->group;
+	if (!mark)
+		return true;
 
+	group = mark->group;
 	/*
 	 * Since acquisition of mark reference is an atomic op as well, we can
 	 * be sure this inc is seen before any effect of refcount increment.
 	 */
 	atomic_inc(&group->user_waits);
+	if (atomic_inc_not_zero(&mark->refcnt))
+		return true;
+
+	if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
+		wake_up(&group->notification_waitq);
 
-	if (iter_info->inode_mark) {
-		/* This can fail if mark is being removed */
-		if (!fsnotify_get_mark_safe(iter_info->inode_mark))
-			goto out_wait;
+	return false;
+}
+
+static void fsnotify_put_mark_wait(struct fsnotify_mark *mark)
+{
+	if (mark) {
+		struct fsnotify_group *group = mark->group;
+
+		fsnotify_put_mark(mark);
+		/*
+		 * We abuse notification_waitq on group shutdown for waiting for
+		 * all marks pinned when waiting for userspace.
+		 */
+		if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
+			wake_up(&group->notification_waitq);
 	}
-	if (iter_info->vfsmount_mark) {
-		if (!fsnotify_get_mark_safe(iter_info->vfsmount_mark))
-			goto out_inode;
+}
+
+bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
+{
+	/* This can fail if mark is being removed */
+	if (!fsnotify_get_mark_safe(iter_info->inode_mark))
+		return false;
+	if (!fsnotify_get_mark_safe(iter_info->vfsmount_mark)) {
+		fsnotify_put_mark_wait(iter_info->inode_mark);
+		return false;
 	}
 
 	/*
@@ -292,34 +306,13 @@ bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
 	srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
 
 	return true;
-out_inode:
-	if (iter_info->inode_mark)
-		fsnotify_put_mark(iter_info->inode_mark);
-out_wait:
-	if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
-		wake_up(&group->notification_waitq);
-	return false;
 }
 
 void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
 {
-	struct fsnotify_group *group = NULL;
-
 	iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
-	if (iter_info->inode_mark) {
-		group = iter_info->inode_mark->group;
-		fsnotify_put_mark(iter_info->inode_mark);
-	}
-	if (iter_info->vfsmount_mark) {
-		group = iter_info->vfsmount_mark->group;
-		fsnotify_put_mark(iter_info->vfsmount_mark);
-	}
-	/*
-	 * We abuse notification_waitq on group shutdown for waiting for all
-	 * marks pinned when waiting for userspace.
-	 */
-	if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
-		wake_up(&group->notification_waitq);
+	fsnotify_put_mark_wait(iter_info->inode_mark);
+	fsnotify_put_mark_wait(iter_info->vfsmount_mark);
 }
 
 /*
-- 
2.5.5