Re: [V9fs-developer] [GIT PULL] 9p file system bug fixes for 2.6.35-rc2

Aneesh Kumar K. V
2010-06-30T18:58:41Z

On Wed, 30 Jun 2010 09:48:15 -0700, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Wed, Jun 30, 2010 at 4:52 AM, Aneesh Kumar K. V
> <aneesh.kumar@linux.vnet.ibm.com> wrote:
> >
> > You are correct. we cannot drop the rename lock in between. I also found
> > another issue in that we are using dentry->d_name.name directly. That
> > would imply we need to hold the rename_lock even during the
> > client_walk.
>
> Yes.
>
> > How about the patch below ?. I updated the patch to hold
> > rename_lock during multiple path walk. Also the rename path is updated
> > to hold the lock during p9_client_rename operations.
>
> I'm not finding any obvious problems with this, and you're right that
> you also need to hold the rename write-lock even for regular renames
> (not just cross-directory ones) in order to protect the name itself.
> So those two patches together seem to be ok at a quick glance.
>
> That said, I do wonder if you wouldn't be better off copying the name
> components in order to then drop the lock earlier. That way you'd only
> need to hold the lock while walking the dentries, and could possibly
> release it during the actual walk (unless you need the names to be
> stable, but I don't think you can rely on that anyway, since other
> clients might be doing renames concurrently.. I don't know)
>
> Linus

Updated patch

>From 0bae321401e88d495ea7e9e96272c11c1b9b9ec3 Mon Sep 17 00:00:00 2001
From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Date: Wed, 30 Jun 2010 19:18:50 +0530
Subject: [PATCH] fs/9p: Prevent parallel rename when doing fid_lookup

During fid lookup we need to make sure that the dentry->d_parent doesn't
change so that we can safely walk the parent dentries. To ensure that
we need to prevent cross directory rename during fid_lookup. Add a
per superblock rename_lock rwlock to prevent parallel fid lookup and rename.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/9p/fid.c | 134 ++++++++++++++++++++++++++++++++++++++---------------
fs/9p/v9fs.c | 1 +
fs/9p/v9fs.h | 1 +
fs/9p/vfs_inode.c | 14 ++++--
fs/9p/vfs_super.c | 1 +
5 files changed, 110 insertions(+), 41 deletions(-)

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 5d6cfcb..7dcefaa 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -97,6 +97,48 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
return ret;
}

+static int build_path_from_dentry(struct v9fs_session_info *v9ses,
+ struct dentry *dentry, char ***names)
+{
+ int n = 0, i;
+ char **wnames;
+ struct dentry *ds;
+
+ read_lock(&v9ses->rename_lock);
+ for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
+ n++;
+
+ wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
+ if (!wnames) {
+ n = 0;
+ goto err_out;
+ }
+ for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent) {
+ wnames[i] = kmalloc(strlen(ds->d_name.name) + 1, GFP_KERNEL);
+ if (!wnames[i])
+ goto err_out;
+
+ strcpy(wnames[i], ds->d_name.name);
+ }
+ *names = wnames;
+ read_unlock(&v9ses->rename_lock);
+ return n;
+err_out:
+ read_unlock(&v9ses->rename_lock);
+ for (; i < n; i++)
+ kfree(wnames[i]);
+ kfree(wnames);
+ return -ENOMEM;
+}
+
+static void kfree_wnames(char **wnames, int n)
+{
+ int i;
+ for (i = 0; i < n; i++)
+ kfree(wnames[i]);
+ kfree(wnames);
+}
+
/**
* v9fs_fid_lookup - lookup for a fid, try to walk if not found
* @dentry: dentry to look for fid in
@@ -112,7 +154,7 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
int i, n, l, clone, any, access;
u32 uid;
struct p9_fid *fid, *old_fid = NULL;
- struct dentry *d, *ds;
+ struct dentry *ds;
struct v9fs_session_info *v9ses;
char **wnames, *uname;

@@ -139,46 +181,62 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
fid = v9fs_fid_find(dentry, uid, any);
if (fid)
return fid;
-
+ /*
+ * we don't have a matching fid. To do a TWALK we need
+ * parent fid. We need to prevent rename when we want to
+ * look at the parent.
+ */
+ read_lock(&v9ses->rename_lock);
ds = dentry->d_parent;
fid = v9fs_fid_find(ds, uid, any);
- if (!fid) { /* walk from the root */
- n = 0;
- for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
- n++;
-
- fid = v9fs_fid_find(ds, uid, any);
- if (!fid) { /* the user is not attached to the fs yet */
- if (access == V9FS_ACCESS_SINGLE)
- return ERR_PTR(-EPERM);
-
- if (v9fs_proto_dotu(v9ses) ||
- v9fs_proto_dotl(v9ses))
+ if (fid) {
+ /*
+ * Found the parent fid do a lookup with that.
+ * We want to do the walk without holding rename_lock
+ */
+ char *dentry_name;
+ dentry_name = kmalloc(strlen(dentry->d_name.name) + 1,
+ GFP_KERNEL);
+ if (dentry_name) {
+ strcpy(dentry_name, dentry->d_name.name);
+ read_unlock(&v9ses->rename_lock);
+ fid = p9_client_walk(fid, 1, (char **)&dentry_name, 1);
+ kfree(dentry_name);
+ goto dentry_out;
+ } else {
+ read_unlock(&v9ses->rename_lock);
+ return ERR_PTR(-ENOMEM);
+ }
+ }
+ read_unlock(&v9ses->rename_lock);
+ /* start from the root and try to do a lookup */
+ fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
+ if (!fid) {
+ /* the user is not attached to the fs yet */
+ if (access == V9FS_ACCESS_SINGLE)
+ return ERR_PTR(-EPERM);
+
+ if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
uname = NULL;
- else
- uname = v9ses->uname;
-
- fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
- v9ses->aname);
+ else
+ uname = v9ses->uname;

- if (IS_ERR(fid))
- return fid;
-
- v9fs_fid_add(ds, fid);
- }
- } else /* walk from the parent */
- n = 1;
+ fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
+ v9ses->aname);
+ if (IS_ERR(fid))
+ return fid;

- if (ds == dentry)
+ v9fs_fid_add(dentry->d_sb->s_root, fid);
+ }
+ /* If we are root just return the fid */
+ if (dentry->d_sb->s_root == dentry)
return fid;

- wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
- if (!wnames)
- return ERR_PTR(-ENOMEM);
-
- for (d = dentry, i = (n-1); i >= 0; i--, d = d->d_parent)
- wnames[i] = (char *) d->d_name.name;
-
+ n = build_path_from_dentry(v9ses, dentry, &wnames);
+ if (n < 0) {
+ fid = ERR_PTR(n);
+ goto err_out;
+ }
clone = 1;
i = 0;
while (i < n) {
@@ -193,16 +251,18 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
*/
p9_client_clunk(old_fid);
}
- kfree(wnames);
- return fid;
+ kfree_wnames(wnames, n);
+ goto err_out;
}
old_fid = fid;
i += l;
clone = 0;
}
+ kfree_wnames(wnames, n);

- kfree(wnames);
+dentry_out:
v9fs_fid_add(dentry, fid);
+err_out:
return fid;
}

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 3c49201..b41bcef 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -237,6 +237,7 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
__putname(v9ses->uname);
return ERR_PTR(-ENOMEM);
}
+ rwlock_init(&v9ses->rename_lock);

rc = bdi_setup_and_register(&v9ses->bdi, "9p", BDI_CAP_MAP_COPY);
if (rc) {
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index bec4d0b..dee4f26 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -104,6 +104,7 @@ struct v9fs_session_info {
struct p9_client *clnt; /* 9p client */
struct list_head slist; /* list of sessions registered with v9fs */
struct backing_dev_info bdi;
+ rwlock_t rename_lock;
};

struct p9_fid *v9fs_session_init(struct v9fs_session_info *, const char *,
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 503a6a2..97fee13 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -964,6 +964,7 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,

sb = dir->i_sb;
v9ses = v9fs_inode2v9ses(dir);
+ /* We can walk d_parent because we hold the dir->i_mutex */
dfid = v9fs_fid_lookup(dentry->d_parent);
if (IS_ERR(dfid))
return ERR_CAST(dfid);
@@ -1070,28 +1071,33 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
retval = PTR_ERR(newdirfid);
goto clunk_olddir;
}
-
if (v9fs_proto_dotl(v9ses)) {
retval = p9_client_rename(oldfid, newdirfid,
(char *) new_dentry->d_name.name);
if (retval != -ENOSYS)
goto clunk_newdir;
}
+ if (old_dentry->d_parent != new_dentry->d_parent) {
+ /*
+ * 9P .u can only handle file rename in the same directory
+ */

- /* 9P can only handle file rename in the same directory */
- if (memcmp(&olddirfid->qid, &newdirfid->qid, sizeof(newdirfid->qid))) {
P9_DPRINTK(P9_DEBUG_ERROR,
"old dir and new dir are different\n");
retval = -EXDEV;
goto clunk_newdir;
}
-
v9fs_blank_wstat(&wstat);
wstat.muid = v9ses->uname;
wstat.name = (char *) new_dentry->d_name.name;
retval = p9_client_wstat(oldfid, &wstat);

clunk_newdir:
+ write_lock(&v9ses->rename_lock);
+ if (!retval)
+ /* successful rename */
+ d_move(old_dentry, new_dentry);
+ write_unlock(&v9ses->rename_lock);
p9_client_clunk(newdirfid);

clunk_olddir:
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 0740675..3abc3ec 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -287,4 +287,5 @@ struct file_system_type v9fs_fs_type = {
.get_sb = v9fs_get_sb,
.kill_sb = v9fs_kill_super,
.owner = THIS_MODULE,
+ .fs_flags = FS_RENAME_DOES_D_MOVE,
};
--
1.7.2.rc0