From: Christian Brauner <christian.brauner@ubuntu.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
linux-fsdevel@vger.kernel.org
Cc: "John Johansen" <john.johansen@canonical.com>,
"James Morris" <jmorris@namei.org>,
"Mimi Zohar" <zohar@linux.ibm.com>,
"Dmitry Kasatkin" <dmitry.kasatkin@gmail.com>,
"Stephen Smalley" <stephen.smalley.work@gmail.com>,
"Casey Schaufler" <casey@schaufler-ca.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Andreas Dilger" <adilger.kernel@dilger.ca>,
"OGAWA Hirofumi" <hirofumi@mail.parknet.co.jp>,
"Geoffrey Thomas" <geofft@ldpreload.com>,
"Mrunal Patel" <mpatel@redhat.com>,
"Josh Triplett" <josh@joshtriplett.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Theodore Tso" <tytso@mit.edu>, "Alban Crequy" <alban@kinvolk.io>,
"Tycho Andersen" <tycho@tycho.ws>,
"David Howells" <dhowells@redhat.com>,
"James Bottomley" <James.Bottomley@hansenpartnership.com>,
"Seth Forshee" <seth.forshee@canonical.com>,
"Stéphane Graber" <stgraber@ubuntu.com>,
"Aleksa Sarai" <cyphar@cyphar.com>,
"Lennart Poettering" <lennart@poettering.net>,
"Eric W. Biederman" <ebiederm@xmission.com>,
smbarber@chromium.org, "Phil Estes" <estesp@gmail.com>,
"Serge Hallyn" <serge@hallyn.com>,
"Kees Cook" <keescook@chromium.org>,
"Todd Kjos" <tkjos@google.com>,
"Paul Moore" <paul@paul-moore.com>,
"Jonathan Corbet" <corbet@lwn.net>,
containers@lists.linux-foundation.org, fstests@vger.kernel.org,
linux-security-module@vger.kernel.org, linux-api@vger.kernel.org,
linux-ext4@vger.kernel.org, linux-integrity@vger.kernel.org,
selinux@vger.kernel.org,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Christoph Hellwig" <hch@lst.de>
Subject: [PATCH v3 03/38] namespace: only take read lock in do_reconfigure_mnt()
Date: Sat, 28 Nov 2020 22:34:52 +0100 [thread overview]
Message-ID: <20201128213527.2669807-4-christian.brauner@ubuntu.com> (raw)
In-Reply-To: <20201128213527.2669807-1-christian.brauner@ubuntu.com>
do_reconfigure_mnt() used to take the down_write(&sb->s_umount) lock
which seems unnecessary since we're not changing the superblock. We're
only checking whether it is already read-only. Setting other mount
attributes is protected by lock_mount_hash() afaict and not by s_umount.
So I think the history of down_write(&sb->s_umount) lock being taken
when setting mount attributes dates back to the introduction of
MNT_READONLY in [2]. Afaict, this introduced the concept of having
read-only mounts in contrast to just having a read-only superblock. When
it got introduced it was simply plumbed into do_remount() which already
took down_write(&sb->s_umount) because it was only used to actually
change the superblock before [2]. Afaict, it would've already been
possible back then to only use down_read(&sb->s_umount) for
MS_BIND | MS_REMOUNT since actual mount options were protected by
the vfsmount lock already. But that would've meant special casing the
locking for MS_BIND | MS_REMOUNT in do_remount() which people might not
have considered worth it.
Then in [1] MS_BIND | MS_REMOUNT mount option changes were split out of
do_remount() into do_reconfigure_mnt() but the down_write(&sb->s_umount)
lock was simply copied over.
Now that we have this be a separate helper only take
the down_read(&sb->s_umount) lock since we're only interested in
checking whether the super block is currently read-only and blocking any
writers from changing it. Essentially, checking that the super block is
read-only has the advantage that we can avoid having to go into the
slowpath and through MNT_WRITE_HOLD and can simply set the read-only
flag on the mount in set_mount_attributes().
[1]: commit 43f5e655eff7 ("vfs: Separate changing mount flags full remount")
[2]: commit 2e4b7fcd9260 ("[PATCH] r/o bind mounts: honor mount writer counts at remount")
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
unchanged
/* v3 */
unchanged
---
fs/namespace.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 798bbf4f48ad..8497d149ecaa 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2512,10 +2512,6 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags)
return 0;
}
-/*
- * Update the user-settable attributes on a mount. The caller must hold
- * sb->s_umount for writing.
- */
static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
{
mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
@@ -2565,13 +2561,17 @@ static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags)
if (!can_change_locked_flags(mnt, mnt_flags))
return -EPERM;
- down_write(&sb->s_umount);
+ /*
+ * We're only checking whether the superblock is read-only not changing
+ * it, so only take down_read(&sb->s_umount).
+ */
+ down_read(&sb->s_umount);
lock_mount_hash();
ret = change_mount_ro_state(mnt, mnt_flags);
if (ret == 0)
set_mount_attributes(mnt, mnt_flags);
unlock_mount_hash();
- up_write(&sb->s_umount);
+ up_read(&sb->s_umount);
mnt_warn_timestamp_expiry(path, &mnt->mnt);
--
2.29.2
next prev parent reply other threads:[~2020-11-28 22:06 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-28 21:34 [PATCH v3 00/38] idmapped mounts Christian Brauner
2020-11-28 21:34 ` [PATCH v3 01/38] namespace: take lock_mount_hash() directly when changing flags Christian Brauner
2020-12-01 10:31 ` Christoph Hellwig
2020-12-02 9:09 ` Christian Brauner
2020-11-28 21:34 ` [PATCH v3 02/38] mount: make {lock,unlock}_mount_hash() static Christian Brauner
2020-12-01 10:32 ` Christoph Hellwig
2020-12-02 9:11 ` Christian Brauner
2020-11-28 21:34 ` Christian Brauner [this message]
2020-12-01 10:32 ` [PATCH v3 03/38] namespace: only take read lock in do_reconfigure_mnt() Christoph Hellwig
2020-12-02 9:14 ` Christian Brauner
2020-11-28 21:34 ` [PATCH v3 04/38] fs: add mount_setattr() Christian Brauner
2020-12-01 10:49 ` Christoph Hellwig
2020-12-02 9:42 ` Christian Brauner
2020-12-02 9:47 ` Christoph Hellwig
2020-12-02 9:55 ` Christoph Hellwig
2020-12-02 9:57 ` Christian Brauner
2020-12-02 10:01 ` Christoph Hellwig
2020-11-28 21:34 ` [PATCH v3 05/38] tests: add mount_setattr() selftests Christian Brauner
2020-11-28 21:34 ` [PATCH v3 06/38] fs: add id translation helpers Christian Brauner
2020-12-01 10:49 ` Christoph Hellwig
2020-12-02 9:16 ` Christian Brauner
2020-11-28 21:34 ` [PATCH v3 07/38] mount: attach mappings to mounts Christian Brauner
2020-12-01 10:50 ` Christoph Hellwig
2020-12-01 13:25 ` Tycho Andersen
2020-12-02 9:24 ` Christian Brauner
2020-11-28 21:34 ` [PATCH v3 08/38] capability: handle idmapped mounts Christian Brauner
2020-11-28 22:34 ` Serge E. Hallyn
2020-11-28 21:34 ` [PATCH v3 09/38] namei: add idmapped mount aware permission helpers Christian Brauner
2020-11-28 22:47 ` Serge E. Hallyn
2020-12-01 10:58 ` Christian Brauner
2020-12-01 10:51 ` Christoph Hellwig
2020-12-01 10:58 ` Christian Brauner
2020-11-28 21:34 ` [PATCH v3 10/38] inode: add idmapped mount aware init and " Christian Brauner
2020-12-01 10:51 ` Christoph Hellwig
2020-12-02 9:17 ` Christian Brauner
2020-11-28 21:35 ` [PATCH v3 11/38] attr: handle idmapped mounts Christian Brauner
2020-11-28 21:35 ` [PATCH v3 12/38] acl: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 13/38] xattr: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 14/38] commoncap: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 15/38] stat: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 16/38] namei: handle idmapped mounts in may_*() helpers Christian Brauner
2020-11-28 21:35 ` [PATCH v3 17/38] namei: introduce struct renamedata Christian Brauner
2020-12-01 10:53 ` Christoph Hellwig
2020-12-02 9:18 ` Christian Brauner
2020-11-28 21:35 ` [PATCH v3 18/38] namei: prepare for idmapped mounts Christian Brauner
2020-11-28 21:35 ` [PATCH v3 19/38] open: handle idmapped mounts in do_truncate() Christian Brauner
2020-11-28 21:35 ` [PATCH v3 20/38] open: handle idmapped mounts Christian Brauner
2020-11-28 21:35 ` [PATCH v3 21/38] af_unix: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 22/38] utimes: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 23/38] fcntl: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 24/38] notify: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 25/38] init: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 26/38] ioctl: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 27/38] would_dump: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 28/38] exec: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 30/38] apparmor: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 31/38] ima: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 32/38] fat: " Christian Brauner
2020-11-30 22:50 ` Mauricio Vásquez Bernal
2020-12-01 10:24 ` Christian Brauner
2020-11-28 21:35 ` [PATCH v3 33/38] ext4: support " Christian Brauner
2020-11-30 22:52 ` Mauricio Vásquez Bernal
2020-12-01 10:28 ` Christian Brauner
2020-12-01 10:54 ` Christoph Hellwig
2020-12-01 11:02 ` Christian Brauner
2020-12-01 11:13 ` Christoph Hellwig
2020-12-01 11:14 ` Christian Brauner
2020-11-28 21:35 ` [PATCH v3 34/38] ecryptfs: do not mount on top of " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 35/38] overlayfs: " Christian Brauner
2020-11-28 21:35 ` [PATCH v3 36/38] fs: introduce MOUNT_ATTR_IDMAP Christian Brauner
2020-11-28 21:35 ` [PATCH v3 37/38] tests: extend mount_setattr tests Christian Brauner
2020-11-28 22:54 ` [PATCH v3 00/38] idmapped mounts Serge E. Hallyn
2020-12-01 10:18 ` Christian Brauner
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