From: Eric Sandeen <sandeen@redhat.com>
To: fsdevel <linux-fsdevel@vger.kernel.org>
Cc: Jan Kara <jack@suse.cz>, Al Viro <viro@ZenIV.linux.org.uk>,
Eric Paris <eparis@redhat.com>
Subject: [PATCH 2/1] fs: call fsnotify_sb_delete after evict_inodes
Date: Wed, 16 Oct 2019 12:11:24 -0500 [thread overview]
Message-ID: <e71d3fbf-8b12-a650-e622-76bc9d4d6a98@redhat.com> (raw)
In-Reply-To: <a26fae1d-a741-6eb1-b460-968a3b97e238@redhat.com>
When a filesystem is unmounted, we currently call fsnotify_sb_delete()
before evict_inodes(), which means that fsnotify_unmount_inodes()
must iterate over all inodes on the superblock, even though it will
only act on inodes with a refcount. This is inefficient and can lead
to livelocks as it iterates over many unrefcounted inodes.
However, since fsnotify_sb_delete() and evict_inodes() are working
on orthogonal sets of inodes (fsnotify_sb_delete() only cares about nonzero
refcount, and evict_inodes() only cares about zero refcount), we can swap
the order of the calls. The fsnotify call will then have a much smaller
list to walk (any refcounted inodes).
This should speed things up overall, and avoid livelocks in
fsnotify_unmount_inodes().
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---
I just did basic sanity testing here, but AFAIK there is no *notify
test suite, so I'm not sure how to really give this a workout.
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ac9eb273e28c..426f03b6e660 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -57,6 +57,10 @@ static void fsnotify_unmount_inodes(struct super_block *sb)
* doing an __iget/iput with SB_ACTIVE clear would actually
* evict all inodes with zero i_count from icache which is
* unnecessarily violent and may in fact be illegal to do.
+ *
+ * However, we should have been called /after/ evict_inodes
+ * removed all zero refcount inodes, in any case. Test to
+ * be sure.
*/
if (!atomic_read(&inode->i_count)) {
spin_unlock(&inode->i_lock);
diff --git a/fs/super.c b/fs/super.c
index cfadab2cbf35..cd352530eca9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -448,10 +448,12 @@ void generic_shutdown_super(struct super_block *sb)
sync_filesystem(sb);
sb->s_flags &= ~SB_ACTIVE;
- fsnotify_sb_delete(sb);
cgroup_writeback_umount();
+ /* evict all inodes with zero refcount */
evict_inodes(sb);
+ /* only nonzero refcount inodes can have marks */
+ fsnotify_sb_delete(sb);
if (sb->s_dio_done_wq) {
destroy_workqueue(sb->s_dio_done_wq);
next prev parent reply other threads:[~2019-10-16 17:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-14 21:30 [PATCH V2] fs: avoid softlockups in s_inodes iterators Eric Sandeen
2019-10-14 21:36 ` Eric Sandeen
2019-10-15 7:37 ` Jan Kara
2019-10-16 2:36 ` Eric Sandeen
2019-10-16 9:42 ` Jan Kara
2019-10-16 13:23 ` Eric Sandeen
2019-10-16 13:49 ` Jan Kara
2019-10-16 14:39 ` Eric Sandeen
2019-10-16 15:26 ` Eric Sandeen
2019-10-16 15:35 ` Jan Kara
2019-10-16 17:11 ` Eric Sandeen [this message]
2019-10-17 8:39 ` [PATCH 2/1] fs: call fsnotify_sb_delete after evict_inodes Jan Kara
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