From: Stephen Brennan <stephen.s.brennan@oracle.com>
To: Jan Kara <jack@suse.cz>, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org,
Amir Goldstein <amir73il@gmail.com>,
linux-kernel@vger.kernel.org,
Stephen Brennan <stephen.s.brennan@oracle.com>
Subject: [PATCH v2 3/3] fsnotify: allow sleepable child flag update
Date: Thu, 20 Oct 2022 18:03:10 -0700 [thread overview]
Message-ID: <20221021010310.29521-4-stephen.s.brennan@oracle.com> (raw)
In-Reply-To: <20221021010310.29521-1-stephen.s.brennan@oracle.com>
With very large d_subdirs lists, iteration can take a long time. Since
iteration needs to hold parent->d_lock, this can trigger soft lockups.
It would be best to make this iteration sleepable. Since we have the
inode locked exclusive, we can drop the parent->d_lock and sleep,
holding a reference to a child dentry, and continue iteration once we
wake.
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---
fs/notify/fsnotify.c | 39 +++++++++++++++++++++++++++++++++++----
1 file changed, 35 insertions(+), 4 deletions(-)
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index f83eca4fb841..061e626127ca 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -102,10 +102,12 @@ void fsnotify_sb_delete(struct super_block *sb)
* on a child we run all of our children and set a dentry flag saying that the
* parent cares. Thus when an event happens on a child it can quickly tell
* if there is a need to find a parent and send the event to the parent.
+ *
+ * Context: inode locked exclusive
*/
bool __fsnotify_update_children_dentry_flags(struct inode *inode)
{
- struct dentry *alias, *child;
+ struct dentry *child, *alias, *last_ref = NULL;
int watched;
if (!S_ISDIR(inode->i_mode))
@@ -119,11 +121,38 @@ bool __fsnotify_update_children_dentry_flags(struct inode *inode)
/* Since this is a directory, there damn well better only be one child */
alias = d_find_any_alias(inode);
- /* run all of the children of the original inode and fix their
- * d_flags to indicate parental interest (their parent is the
- * original inode) */
+ /*
+ * These lists can get very long, so we may need to sleep during
+ * iteration. Normally this would be impossible without a cursor,
+ * but since we have the inode locked exclusive, we're guaranteed
+ * that the directory won't be modified, so whichever dentry we
+ * pick to sleep on won't get moved. So, start a manual iteration
+ * over d_subdirs which will allow us to sleep.
+ */
spin_lock(&alias->d_lock);
+retry:
list_for_each_entry(child, &alias->d_subdirs, d_child) {
+ if (need_resched()) {
+ /*
+ * We need to hold a reference while we sleep. But when
+ * we wake, dput() could free the dentry, invalidating
+ * the list pointers. We can't look at the list pointers
+ * until we re-lock the parent, and we can't dput() once
+ * we have the parent locked. So the solution is to hold
+ * onto our reference and free it the *next* time we drop
+ * alias->d_lock: either at the end of the function, or
+ * at the time of the next sleep.
+ */
+ dget(child);
+ spin_unlock(&alias->d_lock);
+ dput(last_ref);
+ last_ref = child;
+ cond_resched();
+ spin_lock(&alias->d_lock);
+ if (child->d_parent != alias)
+ goto retry;
+ }
+
if (!child->d_inode)
continue;
@@ -135,6 +164,8 @@ bool __fsnotify_update_children_dentry_flags(struct inode *inode)
spin_unlock(&child->d_lock);
}
spin_unlock(&alias->d_lock);
+ if (last_ref)
+ dput(last_ref);
return watched;
}
--
2.34.1
next prev parent reply other threads:[~2022-10-21 1:03 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 22:27 [RFC] fsnotify: allow sleepable child dentry flag update Stephen Brennan
2022-10-13 23:51 ` Al Viro
2022-11-01 21:47 ` Stephen Brennan
2022-10-14 8:01 ` Amir Goldstein
2022-10-17 7:59 ` Stephen Brennan
2022-10-17 11:44 ` Amir Goldstein
2022-10-17 16:59 ` Stephen Brennan
2022-10-17 17:42 ` Amir Goldstein
2022-10-17 9:09 ` Jan Kara
2022-10-18 4:12 ` [PATCH 0/2] fsnotify: fix softlockups iterating over d_subdirs Stephen Brennan
2022-10-18 4:12 ` [PATCH 1/2] fsnotify: Protect i_fsnotify_mask and child flags with inode rwsem Stephen Brennan
2022-10-18 7:39 ` Amir Goldstein
2022-10-21 0:33 ` Stephen Brennan
2022-10-21 7:22 ` Amir Goldstein
2022-10-18 4:12 ` [PATCH 2/2] fsnotify: allow sleepable child flag update Stephen Brennan
2022-10-18 5:36 ` Amir Goldstein
2022-10-27 7:50 ` kernel test robot
2022-10-27 8:44 ` Yujie Liu
2022-10-27 22:12 ` Stephen Brennan
2022-10-18 8:07 ` [PATCH 0/2] fsnotify: fix softlockups iterating over d_subdirs Amir Goldstein
2022-10-18 23:52 ` Stephen Brennan
2022-10-19 5:33 ` Amir Goldstein
2022-10-27 22:06 ` Stephen Brennan
2022-10-28 8:58 ` Amir Goldstein
2022-10-21 1:03 ` [PATCH v2 0/3] " Stephen Brennan
2022-10-21 1:03 ` [PATCH v2 1/3] fsnotify: Use d_find_any_alias to get dentry associated with inode Stephen Brennan
2022-10-21 9:25 ` Amir Goldstein
2022-10-21 1:03 ` [PATCH v2 2/3] fsnotify: Protect i_fsnotify_mask and child flags with inode rwsem Stephen Brennan
2022-10-21 4:01 ` kernel test robot
2022-10-21 8:22 ` Amir Goldstein
2022-10-21 9:18 ` Amir Goldstein
2022-10-25 18:02 ` Stephen Brennan
2022-10-26 5:41 ` Amir Goldstein
2022-10-21 9:17 ` Christian Brauner
2022-10-21 9:21 ` Amir Goldstein
2022-10-21 1:03 ` Stephen Brennan [this message]
2022-10-28 0:10 ` [PATCH v3 0/3] fsnotify: fix softlockups iterating over d_subdirs Stephen Brennan
2022-10-28 0:10 ` [PATCH v3 1/3] fsnotify: Use d_find_any_alias to get dentry associated with inode Stephen Brennan
2022-11-10 1:12 ` Stephen Brennan
2022-10-28 0:10 ` [PATCH v3 2/3] fsnotify: Protect i_fsnotify_mask and child flags with inode rwsem Stephen Brennan
2022-10-28 9:11 ` Amir Goldstein
2022-11-10 0:03 ` kernel test robot
2022-11-10 1:06 ` Stephen Brennan
2022-10-28 0:10 ` [PATCH v3 3/3] fsnotify: allow sleepable child flag update Stephen Brennan
2022-10-28 9:32 ` Amir Goldstein
2022-11-01 21:25 ` Stephen Brennan
2022-11-01 17:51 ` [PATCH v3 0/3] fsnotify: fix softlockups iterating over d_subdirs Jan Kara
2022-11-01 20:48 ` Stephen Brennan
2022-11-02 8:55 ` Amir Goldstein
2022-11-10 20:04 ` Stephen Brennan
2022-11-02 17:52 ` Jan Kara
2022-11-04 23:33 ` Stephen Brennan
2022-11-07 11:56 ` Jan Kara
2022-11-11 22:06 ` [PATCH v4 0/5] " Stephen Brennan
2022-11-11 22:06 ` [PATCH v4 1/5] fsnotify: clear PARENT_WATCHED flags lazily Stephen Brennan
2022-11-11 22:06 ` [PATCH v4 2/5] fsnotify: Use d_find_any_alias to get dentry associated with inode Stephen Brennan
2022-11-12 8:53 ` Amir Goldstein
2022-11-11 22:06 ` [PATCH v4 3/5] dnotify: move fsnotify_recalc_mask() outside spinlock Stephen Brennan
2022-11-12 9:06 ` Amir Goldstein
2022-11-11 22:06 ` [PATCH v4 4/5] fsnotify: allow sleepable child flag update Stephen Brennan
2022-11-12 10:00 ` Amir Goldstein
2022-11-15 7:10 ` kernel test robot
2022-11-11 22:06 ` [PATCH v4 5/5] fsnotify: require inode lock held during " Stephen Brennan
2022-11-12 9:42 ` Amir Goldstein
2022-11-11 22:08 ` [PATCH v4 0/5] fsnotify: fix softlockups iterating over d_subdirs Stephen Brennan
2022-11-22 11:50 ` Jan Kara
2022-11-22 14:03 ` Amir Goldstein
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