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Subject[PATCH 5.4 02/15] devtmpfs regression fix: reconfigure on each mount
Date
From: NeilBrown <neilb@suse.de>

commit a6097180d884ddab769fb25588ea8598589c218c upstream.

Prior to Linux v5.4 devtmpfs used mount_single() which treats the given
mount options as "remount" options, so it updates the configuration of
the single super_block on each mount.

Since that was changed, the mount options used for devtmpfs are ignored.
This is a regression which affect systemd - which mounts devtmpfs with
"-o mode=755,size=4m,nr_inodes=1m".

This patch restores the "remount" effect by calling reconfigure_single()

Fixes: d401727ea0d7 ("devtmpfs: don't mix {ramfs,shmem}_fill_super() with mount_single()")
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/base/devtmpfs.c | 8 ++++++++
fs/super.c | 4 ++--
include/linux/fs_context.h | 2 ++
3 files changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -25,6 +25,7 @@
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/kthread.h>
+#include <linux/fs_context.h>
#include <uapi/linux/mount.h>
#include "base.h"

@@ -62,8 +63,15 @@ static struct dentry *public_dev_mount(s
const char *dev_name, void *data)
{
struct super_block *s = mnt->mnt_sb;
+ int err;
+
atomic_inc(&s->s_active);
down_write(&s->s_umount);
+ err = reconfigure_single(s, flags, data);
+ if (err < 0) {
+ deactivate_locked_super(s);
+ return ERR_PTR(err);
+ }
return dget(s->s_root);
}

--- a/fs/super.c
+++ b/fs/super.c
@@ -1470,8 +1470,8 @@ struct dentry *mount_nodev(struct file_s
}
EXPORT_SYMBOL(mount_nodev);

-static int reconfigure_single(struct super_block *s,
- int flags, void *data)
+int reconfigure_single(struct super_block *s,
+ int flags, void *data)
{
struct fs_context *fc;
int ret;
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -135,6 +135,8 @@ extern int generic_parse_monolithic(stru
extern int vfs_get_tree(struct fs_context *fc);
extern void put_fs_context(struct fs_context *fc);
extern void fc_drop_locked(struct fs_context *fc);
+int reconfigure_single(struct super_block *s,
+ int flags, void *data);

/*
* sget() wrappers to be called from the ->get_tree() op.

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