Omar Sandoval <osandov@xxxxxxxxxxx> writes:
> On Fri, May 15, 2015 at 08:58:20PM +0200, Ivan Delalande wrote:
>> Hi,
>>
>> I’m still struggling to understand all the relations between the VFS
>> structures and at which point they get initialized precisely. Do you
>> have any idea how to fix this problem?
The relationships in this case are quite odd and can be simplified.
> I'm attaching a minimal script that reproduces this on 4.1-rc4. I'm
> taking a look, but Eric or Al will probably figure this out before I get
> the chance :)
This works for me, can you confirm it works for you folks as well?
Thank you,
Eric
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Date: Wed, 20 May 2015 16:39:00 -0500
Subject: [PATCH] vfs: Fix, simpliy and stop using d_dname for the /proc/*/ns/* files.
Now that these files are no longer in proc we can stop playing games
with d_alloc_pseudo and d_dname. This change causes a couple of user
visible changes:
- Opening /proc/*/ns/* and then readlink on /proc/self/fd/N now sees a
prepended / in the filename.
- /proc/mountinfo now gives useful information on what is mounted.
- Bind mounting /proc/*/ns/*, opening the mounted file, removing the
bind mount, and readlink on /proc/self/fd/N now sees / (as it should)
instead of triggering a warning and a kernel stack backtrace from
prepend_path.
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Ivan Delalande <colona@xxxxxxxxxx>
Reported-by: Omar Sandoval <osandov@xxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
fs/dcache.c | 7 +------
fs/nsfs.c | 19 +++++--------------
2 files changed, 6 insertions(+), 20 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index 656ce522a218..e0f0967ef24c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3087,13 +3087,8 @@ char *d_path(const struct path *path, char *buf, int buflen)
* thus don't need to be hashed. They also don't need a name until a
* user wants to identify the object in /proc/pid/fd/. The little hack
* below allows us to generate a name for these objects on demand:
- *
- * Some pseudo inodes are mountable. When they are mounted
- * path->dentry == path->mnt->mnt_root. In that case don't call d_dname
- * and instead have d_path return the mounted path.
*/
- if (path->dentry->d_op && path->dentry->d_op->d_dname &&
- (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
+ if (path->dentry->d_op && path->dentry->d_op->d_dname)
return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
rcu_read_lock();
diff --git a/fs/nsfs.c b/fs/nsfs.c
index 99521e7c492b..b9ecfa6cb46d 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -11,15 +11,6 @@ static const struct file_operations ns_file_operations = {
.llseek = no_llseek,
};
-static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
-{
- struct inode *inode = d_inode(dentry);
- const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
-
- return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
- ns_ops->name, inode->i_ino);
-}
-
static void ns_prune_dentry(struct dentry *dentry)
{
struct inode *inode = d_inode(dentry);
@@ -33,7 +24,6 @@ const struct dentry_operations ns_dentry_operations =
{
.d_prune = ns_prune_dentry,
.d_delete = always_delete_dentry,
- .d_dname = ns_dname,
};
static void nsfs_evict(struct inode *inode)
@@ -47,7 +37,7 @@ void *ns_get_path(struct path *path, struct task_struct *task,
const struct proc_ns_operations *ns_ops)
{
struct vfsmount *mnt = mntget(nsfs_mnt);
- struct qstr qname = { .name = "", };
+ char name[DNAME_INLINE_LEN];
struct dentry *dentry;
struct inode *inode;
struct ns_common *ns;
@@ -80,6 +70,7 @@ slow:
mntput(mnt);
return ERR_PTR(-ENOMEM);
}
+ snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns->inum);
inode->i_ino = ns->inum;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->i_flags |= S_IMMUTABLE;
@@ -87,13 +78,13 @@ slow:
inode->i_fop = &ns_file_operations;
inode->i_private = ns;
- dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
+ dentry = d_alloc_name(mnt->mnt_root, name);
if (!dentry) {
iput(inode);
mntput(mnt);
return ERR_PTR(-ENOMEM);
}
- d_instantiate(dentry, inode);
+ d_add(dentry, inode);
dentry->d_fsdata = (void *)ns_ops;
d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
if (d) {
@@ -143,7 +134,7 @@ static const struct super_operations nsfs_ops = {
static struct dentry *nsfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
- return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
+ return mount_pseudo(fs_type, "/", &nsfs_ops,
&ns_dentry_operations, NSFS_MAGIC);
}
static struct file_system_type nsfs = {
--
2.2.1
--
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