linux-kernel - [PATCH] fs: don't remove inotify watchers from alive inode-s (v2)

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Date:	Fri, 19 Sep 2014 19:45:16 +0400
From:	Andrey Vagin <avagin@...nvz.org>
To:	linux-fsdevel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Heinrich Schuchardt <xypron.debian@....de>,
	Jan Kara <jack@...e.cz>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>,
	Eric Paris <eparis@...isplace.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: [PATCH] fs: don't remove inotify watchers from alive inode-s (v2)

Currently watchers are removed in dentry_iput(), if n_link is zero.  But
other detries can be linked with this inode.

For example if we create two hard links, open the first one and set an
inotify watcher on one of them.  Then if we remove the opened file and
then another file, the inotify watcher will be removed. But we will have
the alive file descriptor, which allows us to generate more events.

And here is another behaviour, if files are removed in another order.
The watcher will not be removed and we will keep getting inotify events
for that inode.

This patch removes difference of behaviours for these cases. Watchers
are removed, only if nlink is zero and i_dentry list is empty. The
resulting behaviour is the same with what has been described in the
second case.

Look at a following example:

	fd = inotify_init1(IN_NONBLOCK);
	deleted = open(path, O_CREAT | O_TRUNC | O_WRONLY, 0666);
	link(path, path_link);

	wd_deleted = inotify_add_watch(fd, path_link, IN_ALL_EVENTS);

	unlink(path);
	unlink(path_link);

	printf(" --- unlink path, path_link\n");
	read_evetns(fd);

	close(deleted);
	printf(" --- close\n");
	read_evetns(fd);
	printf(" --- end\n");

We expect to get the same set of events for this case and for the
case, when files are deleted in another order. But now we get the
different set of events.

Without this patch:
The first case, when "path" is deleted before "path_link"
 --- unlink path, path_link
4	(IN_ATTRIB)
400	(IN_DELETE_SELF)
8000	(IN_IGNORED)
 --- close
 --- end

and for the case, when "path_link" is deleted before "path"
 --- unlink path_link, path
4	(IN_ATTRIB)
 --- close
8	(IN_CLOSE_WRITE)
400	(IN_DELETE_SELF)
8000	(IN_IGNORED)
 --- end

With this patch we have the same output for both cases:
 --- unlink
4	(IN_ATTRIB)
 --- close
8	(IN_CLOSE_WRITE)
400	(IN_DELETE_SELF)
8000	(IN_IGNORED)
 --- end
PASS

v2: generate IN_DELETE_SELF when the last link to the file is removed

Reviewed-by: Jan Kara <jack@...e.cz>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc: Heinrich Schuchardt <xypron.debian@....de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: John McCutchan <john@...nmccutchan.com>
Cc: Robert Love <rlove@...ve.org>
Cc: Eric Paris <eparis@...isplace.org>
Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Pavel Emelyanov <xemul@...allels.com>
Signed-off-by: Andrey Vagin <avagin@...nvz.org>
---
 fs/dcache.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 7a5b514..3a0e3bc 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -278,12 +278,15 @@ static void dentry_iput(struct dentry * dentry)
 	__releases(dentry->d_inode->i_lock)
 {
 	struct inode *inode = dentry->d_inode;
+	bool last_dentry;
+
 	if (inode) {
 		dentry->d_inode = NULL;
 		hlist_del_init(&dentry->d_alias);
+		last_dentry = hlist_empty(&inode->i_dentry);
 		spin_unlock(&dentry->d_lock);
 		spin_unlock(&inode->i_lock);
-		if (!inode->i_nlink)
+		if (!inode->i_nlink && last_dentry)
 			fsnotify_inoderemove(inode);
 		if (dentry->d_op && dentry->d_op->d_iput)
 			dentry->d_op->d_iput(dentry, inode);
@@ -303,13 +306,16 @@ static void dentry_unlink_inode(struct dentry * dentry)
 	__releases(dentry->d_inode->i_lock)
 {
 	struct inode *inode = dentry->d_inode;
+	bool last_dentry;
+
 	__d_clear_type(dentry);
 	dentry->d_inode = NULL;
 	hlist_del_init(&dentry->d_alias);
 	dentry_rcuwalk_barrier(dentry);
+	last_dentry = hlist_empty(&inode->i_dentry);
 	spin_unlock(&dentry->d_lock);
 	spin_unlock(&inode->i_lock);
-	if (!inode->i_nlink)
+	if (!inode->i_nlink && last_dentry)
 		fsnotify_inoderemove(inode);
 	if (dentry->d_op && dentry->d_op->d_iput)
 		dentry->d_op->d_iput(dentry, inode);
-- 
1.9.3

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