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fs/9p: Prevent parallel rename when doing fid_lookup

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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_sem rw_semaphore to prevent parallel fid lookup and
rename.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
This commit is contained in:
Aneesh Kumar K.V
2010-06-30 19:18:50 +05:30
committed by Eric Van Hensbergen
parent ebf46264a0
commit a534c8d15b
5 changed files with 90 additions and 38 deletions
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112
fs/9p/fid.c
View File

@@ -97,6 +97,34 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
return ret;
}
/*
* We need to hold v9ses->rename_sem as long as we hold references
* to returned path array. Array element contain pointers to
* dentry names.
*/
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;
for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
n++;
wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
if (!wnames)
goto err_out;
for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
wnames[i] = (char *)ds->d_name.name;
*names = wnames;
return n;
err_out:
return -ENOMEM;
}
/**
* v9fs_fid_lookup - lookup for a fid, try to walk if not found
* @dentry: dentry to look for fid in
@@ -112,7 +140,7 @@ 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;
@@ -139,50 +167,62 @@ 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.
*/
down_read(&v9ses->rename_sem);
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++;
if (fid) {
/* Found the parent fid do a lookup with that */
fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
goto fid_out;
}
up_read(&v9ses->rename_sem);
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);
/* 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))
if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
uname = NULL;
else
uname = v9ses->uname;
else
uname = v9ses->uname;
fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
v9ses->aname);
fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
v9ses->aname);
if (IS_ERR(fid))
return fid;
if (IS_ERR(fid))
return fid;
v9fs_fid_add(ds, fid);
}
} else /* walk from the parent */
n = 1;
if (ds == dentry)
v9fs_fid_add(dentry->d_sb->s_root, fid);
}
/* If we are root ourself just return that */
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;
/*
* Do a multipath walk with attached root.
* When walking parent we need to make sure we
* don't have a parallel rename happening
*/
down_read(&v9ses->rename_sem);
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) {
l = min(n - i, P9_MAXWELEM);
/*
* We need to hold rename lock when doing a multipath
* walk to ensure none of the patch component change
*/
fid = p9_client_walk(fid, l, &wnames[i], clone);
if (IS_ERR(fid)) {
if (old_fid) {
@@ -194,15 +234,17 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
p9_client_clunk(old_fid);
}
kfree(wnames);
return fid;
goto err_out;
}
old_fid = fid;
i += l;
clone = 0;
}
kfree(wnames);
fid_out:
v9fs_fid_add(dentry, fid);
err_out:
up_read(&v9ses->rename_sem);
return fid;
}