linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Minchan Kim <minchan@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tejun Heo <tj@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Minchan Kim <minchan@kernel.org>
Subject: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation
Date: Tue, 16 Nov 2021 11:43:17 -0800	[thread overview]
Message-ID: <20211116194317.1430399-1-minchan@kernel.org> (raw)

The kernfs implementation has big lock granularity(kernfs_rwsem) so
every kernfs-based(e.g., sysfs, cgroup, dmabuf) fs are able to compete
the lock. Thus, if one of userspace goes the sleep under holding
the lock for a long time, rest of them should wait it. A example is
the holder goes direct reclaim with the lock since it needs memory
allocation. Let's fix it at common technique that release the lock
and then allocate the memory. Fortunately, kernfs looks like have
an refcount so I hope it's fine.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 fs/kernfs/dir.c             | 14 +++++++++++---
 fs/kernfs/inode.c           |  2 +-
 fs/kernfs/kernfs-internal.h |  1 +
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 8e0a1378a4b1..ecdb2975060d 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1119,9 +1119,17 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 			up_read(&kernfs_rwsem);
 			return NULL;
 		}
-		inode = kernfs_get_inode(dir->i_sb, kn);
-		if (!inode)
-			inode = ERR_PTR(-ENOMEM);
+		kernfs_get(kn);
+		up_read(&kernfs_rwsem);
+		inode = iget_locked(dir->i_sb, kernfs_ino(kn));
+		if (!inode) {
+			kernfs_put(kn);
+			return ERR_PTR(-ENOMEM);
+		}
+		down_read(&kernfs_rwsem);
+		if (inode->i_state & I_NEW)
+			kernfs_init_inode(kn, inode);
+		kernfs_put(kn);
 	}
 	/*
 	 * Needed for negative dentry validation.
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index c0eae1725435..6e2004010435 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -195,7 +195,7 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
 	return 0;
 }
 
-static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
+void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
 {
 	kernfs_get(kn);
 	inode->i_private = kn;
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index f9cc912c31e1..eef7656f7cd8 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -118,6 +118,7 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
 		       u32 request_mask, unsigned int query_flags);
 ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size);
 int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
+void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode);
 
 /*
  * dir.c
-- 
2.34.0.rc1.387.gb447b232ab-goog


             reply	other threads:[~2021-11-16 19:43 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-16 19:43 Minchan Kim [this message]
2021-11-16 19:49 ` Greg Kroah-Hartman
2021-11-16 21:36   ` Minchan Kim
2021-11-17  6:44     ` Greg Kroah-Hartman
2021-11-17  7:27       ` Minchan Kim
2021-11-17  7:39         ` Greg Kroah-Hartman
2021-11-17 21:43           ` Minchan Kim
2021-11-17 21:45         ` Tejun Heo
2021-11-17 22:13           ` Minchan Kim
2021-11-17 22:23             ` Tejun Heo
2021-11-18  1:55               ` Minchan Kim
2021-11-18 16:35                 ` Tejun Heo

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211116194317.1430399-1-minchan@kernel.org \
    --to=minchan@kernel.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=tj@kernel.org \
    --subject='Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).