[RFC PATCH v4 09/17] ceph: make ceph_msdc_build_path use ref-walk

Jeff Layton
2021-01-20T18:33:47Z

Encryption potentially requires allocation, at which point we'll need to
be in a non-atomic context. Convert ceph_msdc_build_path to take dentry
spinlocks and references instead of using rcu_read_lock to walk the
path.

This is slightly less efficient, and we may want to eventually allow
using RCU when the leaf dentry isn't encrypted.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/ceph/mds_client.c | 35 +++++++++++++++++++----------------
1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 45c06873f28c..77cee8a0de3f 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2323,7 +2323,8 @@ static inline u64 __get_oldest_tid(struct ceph_mds_client *mdsc)
char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *pbase,
int stop_on_nosnap)
{
- struct dentry *temp;
+ struct dentry *cur;
+ struct inode *inode;
char *path;
int pos;
unsigned seq;
@@ -2340,34 +2341,35 @@ char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *pbase,
path[pos] = '\0';

seq = read_seqbegin(&rename_lock);
- rcu_read_lock();
- temp = dentry;
+ cur = dget(dentry);
for (;;) {
- struct inode *inode;
+ struct dentry *temp;

- spin_lock(&temp->d_lock);
- inode = d_inode(temp);
+ spin_lock(&cur->d_lock);
+ inode = d_inode(cur);
if (inode && ceph_snap(inode) == CEPH_SNAPDIR) {
dout("build_path path+%d: %p SNAPDIR\n",
- pos, temp);
- } else if (stop_on_nosnap && inode && dentry != temp &&
+ pos, cur);
+ } else if (stop_on_nosnap && inode && dentry != cur &&
ceph_snap(inode) == CEPH_NOSNAP) {
- spin_unlock(&temp->d_lock);
+ spin_unlock(&cur->d_lock);
pos++; /* get rid of any prepended '/' */
break;
} else {
- pos -= temp->d_name.len;
+ pos -= cur->d_name.len;
if (pos < 0) {
- spin_unlock(&temp->d_lock);
+ spin_unlock(&cur->d_lock);
break;
}
- memcpy(path + pos, temp->d_name.name, temp->d_name.len);
+ memcpy(path + pos, cur->d_name.name, cur->d_name.len);
}
+ temp = cur;
spin_unlock(&temp->d_lock);
- temp = READ_ONCE(temp->d_parent);
+ cur = dget_parent(temp);
+ dput(temp);

/* Are we at the root? */
- if (IS_ROOT(temp))
+ if (IS_ROOT(cur))
break;

/* Are we out of buffer? */
@@ -2376,8 +2378,9 @@ char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *pbase,

path[pos] = '/';
}
- base = ceph_ino(d_inode(temp));
- rcu_read_unlock();
+ inode = d_inode(cur);
+ base = inode ? ceph_ino(inode) : 0;
+ dput(cur);

if (read_seqretry(&rename_lock, seq))
goto retry;
--
2.29.2