Ben reported tripping the BUG_ON in create_request_message during some
performance testing. Analysis of the vmcore showed that the length of
the r_dentry->d_name string changed after we allocated the buffer, but
before we encoded it.
build_dentry_path returns pointers to d_name in the common case of
non-snapped dentries, but this optimization isn't safe unless the parent
directory is locked. When it isn't, have the code make a copy of the
d_name while holding the d_lock.
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Ben England <bengland@xxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
fs/ceph/mds_client.c | 60 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 49 insertions(+), 11 deletions(-)
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 747ac3585519..4817efaa7def 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2168,10 +2168,38 @@ char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *base,
return path;
}
+/* Duplicate the dentry->d_name.name safely */
+static int clone_dentry_name(struct dentry *dentry, const char **ppath,
+ int *ppathlen)
+{
+ u32 len;
+ char *name;
+retry:
+ len = READ_ONCE(dentry->d_name.len);
+ name = kmalloc(len + 1, GFP_NOFS);
+ if (!name)
+ return -ENOMEM;
+
+ spin_lock(&dentry->d_lock);
+ if (dentry->d_name.len != len) {
+ spin_unlock(&dentry->d_lock);
+ kfree(name);
+ goto retry;
+ }
+ memcpy(name, dentry->d_name.name, len);
+ spin_unlock(&dentry->d_lock);
+
+ name[len] = '\0';
+ *ppath = name;
+ *ppathlen = len;
+ return 0;
+}
+
static int build_dentry_path(struct dentry *dentry, struct inode *dir,
const char **ppath, int *ppathlen, u64 *pino,
- int *pfreepath)
+ bool *pfreepath, bool parent_locked)
{
+ int ret;
char *path;
rcu_read_lock();
@@ -2180,8 +2208,15 @@ static int build_dentry_path(struct dentry *dentry, struct inode *dir,
if (dir && ceph_snap(dir) == CEPH_NOSNAP) {
*pino = ceph_ino(dir);
rcu_read_unlock();
- *ppath = dentry->d_name.name;
- *ppathlen = dentry->d_name.len;
+ if (parent_locked) {
+ *ppath = dentry->d_name.name;
+ *ppathlen = dentry->d_name.len;
+ } else {
+ ret = clone_dentry_name(dentry, ppath, ppathlen);
+ if (ret)
+ return ret;
+ *pfreepath = true;
+ }
return 0;
}
rcu_read_unlock();
@@ -2189,13 +2224,13 @@ static int build_dentry_path(struct dentry *dentry, struct inode *dir,
if (IS_ERR(path))
return PTR_ERR(path);
*ppath = path;
- *pfreepath = 1;
+ *pfreepath = true;
return 0;
}
static int build_inode_path(struct inode *inode,
const char **ppath, int *ppathlen, u64 *pino,
- int *pfreepath)
+ bool *pfreepath)
{
struct dentry *dentry;
char *path;
@@ -2211,7 +2246,7 @@ static int build_inode_path(struct inode *inode,
if (IS_ERR(path))
return PTR_ERR(path);
*ppath = path;
- *pfreepath = 1;
+ *pfreepath = true;
return 0;
}
@@ -2222,7 +2257,7 @@ static int build_inode_path(struct inode *inode,
static int set_request_path_attr(struct inode *rinode, struct dentry *rdentry,
struct inode *rdiri, const char *rpath,
u64 rino, const char **ppath, int *pathlen,
- u64 *ino, int *freepath)
+ u64 *ino, bool *freepath, bool parent_locked)
{
int r = 0;
@@ -2232,7 +2267,7 @@ static int set_request_path_attr(struct inode *rinode, struct dentry *rdentry,
ceph_snap(rinode));
} else if (rdentry) {
r = build_dentry_path(rdentry, rdiri, ppath, pathlen, ino,
- freepath);
+ freepath, parent_locked);
dout(" dentry %p %llx/%.*s\n", rdentry, *ino, *pathlen,
*ppath);
} else if (rpath || rino) {
@@ -2258,7 +2293,7 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
const char *path2 = NULL;
u64 ino1 = 0, ino2 = 0;
int pathlen1 = 0, pathlen2 = 0;
- int freepath1 = 0, freepath2 = 0;
+ bool freepath1 = false, freepath2 = false;
int len;
u16 releases;
void *p, *end;
@@ -2266,16 +2301,19 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
ret = set_request_path_attr(req->r_inode, req->r_dentry,
req->r_parent, req->r_path1, req->r_ino1.ino,
- &path1, &pathlen1, &ino1, &freepath1);
+ &path1, &pathlen1, &ino1, &freepath1,
+ test_bit(CEPH_MDS_R_PARENT_LOCKED,
+ &req->r_req_flags));
if (ret < 0) {
msg = ERR_PTR(ret);
goto out;
}
+ /* If r_old_dentry is set, then assume that its parent is locked */
ret = set_request_path_attr(NULL, req->r_old_dentry,
req->r_old_dentry_dir,
req->r_path2, req->r_ino2.ino,
- &path2, &pathlen2, &ino2, &freepath2);
+ &path2, &pathlen2, &ino2, &freepath2, true);
if (ret < 0) {
msg = ERR_PTR(ret);
goto out_free1;
