[Devel] [PATCH RHEL7 COMMIT] ms/fs: split out functions to hold writers

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1160.88.1.vz7.195.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.88.1.vz7.195.2
------>
commit a95a15596e23a2da6d9d097001842fc1c78e6046
Author: Christian Brauner <christian.brauner at ubuntu.com>
Date:   Thu Apr 13 18:47:22 2023 +0800

    ms/fs: split out functions to hold writers
    
    When a mount is marked read-only we set MNT_WRITE_HOLD on it if there
    aren't currently any active writers. Split this logic out into simple
    helpers that we can use in follow-up patches.
    
    Link: https://lore.kernel.org/r/20210121131959.646623-33-christian.brauner@ubuntu.com
    Cc: David Howells <dhowells at redhat.com>
    Cc: Al Viro <viro at zeniv.linux.org.uk>
    Cc: linux-fsdevel at vger.kernel.org
    Suggested-by: Christoph Hellwig <hch at lst.de>
    Reviewed-by: Christoph Hellwig <hch at lst.de>
    Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
    
    (cherry picked from commit fbdc2f6c40f6528fa0db79c73e844451234f3e26)
    https://jira.sw.ru/browse/PSBM-144416
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    =================
    Patchset description:
    mount: Port move_mount_set_group and mount_setattr
    
    We need this as in Virtuozzo criu after rebase to mainstream criu in u20
    we will switch to this new API for sharing group setting accross mounts.
    
    https://jira.vzint.dev/browse/PSBM-144416
---
 fs/namespace.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index c03e21575d08..a40a217f9871 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -570,10 +570,8 @@ void mnt_drop_write_file(struct file *file)
 }
 EXPORT_SYMBOL(mnt_drop_write_file);
 
-static int mnt_make_readonly(struct mount *mnt)
+static inline int mnt_hold_writers(struct mount *mnt)
 {
-	int ret = 0;
-
 	mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 	/*
 	 * After storing MNT_WRITE_HOLD, we'll read the counters. This store
@@ -598,15 +596,29 @@ static int mnt_make_readonly(struct mount *mnt)
 	 * we're counting up here.
 	 */
 	if (mnt_get_writers(mnt) > 0)
-		ret = -EBUSY;
-	else
-		mnt->mnt.mnt_flags |= MNT_READONLY;
+		return -EBUSY;
+
+	return 0;
+}
+
+static inline void mnt_unhold_writers(struct mount *mnt)
+{
 	/*
 	 * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
 	 * that become unheld will see MNT_READONLY.
 	 */
 	smp_wmb();
 	mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+}
+
+static int mnt_make_readonly(struct mount *mnt)
+{
+	int ret;
+
+	ret = mnt_hold_writers(mnt);
+	if (!ret)
+		mnt->mnt.mnt_flags |= MNT_READONLY;
+	mnt_unhold_writers(mnt);
 	return ret;
 }