dentry->d_fsdata is set to NFS_FSDATA_BLOCKED while unlinking or
renaming-over a file to ensure that no open succeeds while the NFS
operation progressed on the server.
Setting dentry->d_fsdata to NFS_FSDATA_BLOCKED is done under ->d_lock
after checking the refcount is not elevated. Any attempt to open the
file (through that name) will go through lookp_open() which will take
->d_lock while incrementing the refcount, we can be sure that once the
new value is set, __nfs_lookup_revalidate() *will* see the new value and
will block.
We don't have any locking guarantee that when we set ->d_fsdata to NULL,
the wait_var_event() in __nfs_lookup_revalidate() will notice.
wait/wake primitives do NOT provide barriers to guarantee order. We
must use smp_load_acquire() in wait_var_event() to ensure we look at an
up-to-date value, and must use smp_store_release() before wake_up_var().
This patch adds those barrier functions and factors out
block_revalidate() and unblock_revalidate() far clarity.
There is also a hypothetical bug in that if memory allocation fails
(which never happens in practice) we might leave ->d_fsdata locked.
This patch adds the missing call to unblock_revalidate().
Reported-and-tested-by: Richard Kojedzinszky <[email protected]>
Closes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1071501
Fixes: 3c59366c207e ("NFS: don't unhash dentry during unlink/rename")
Signed-off-by: NeilBrown <[email protected]>
---
fs/nfs/dir.c | 47 ++++++++++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 15 deletions(-)
v1 incorrectly assigned NULL to ->d_fsdata in block_revalidate().
It should assign NFS_FSDATA_BLOCKED.
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index ac505671efbd..bdd6cb33a370 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1802,9 +1802,10 @@ __nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags,
if (parent != READ_ONCE(dentry->d_parent))
return -ECHILD;
} else {
- /* Wait for unlink to complete */
+ /* Wait for unlink to complete - see unblock_revalidate() */
wait_var_event(&dentry->d_fsdata,
- dentry->d_fsdata != NFS_FSDATA_BLOCKED);
+ smp_load_acquire(&dentry->d_fsdata)
+ != NFS_FSDATA_BLOCKED);
parent = dget_parent(dentry);
ret = reval(d_inode(parent), dentry, flags);
dput(parent);
@@ -1817,6 +1818,29 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
return __nfs_lookup_revalidate(dentry, flags, nfs_do_lookup_revalidate);
}
+static void block_revalidate(struct dentry *dentry)
+{
+ /* old devname - just in case */
+ kfree(dentry->d_fsdata);
+
+ /* Any new reference that could lead to an open
+ * will take ->d_lock in lookup_open() -> d_lookup().
+ * Holding this lock ensures we cannot race with
+ * __nfs_lookup_revalidate() and removes and need
+ * for further barriers.
+ */
+ lockdep_assert_held(&dentry->d_lock);
+
+ dentry->d_fsdata = NFS_FSDATA_BLOCKED;
+}
+
+static void unblock_revalidate(struct dentry *dentry)
+{
+ /* store_release ensures wait_var_event() sees the update */
+ smp_store_release(&dentry->d_fsdata, NULL);
+ wake_up_var(&dentry->d_fsdata);
+}
+
/*
* A weaker form of d_revalidate for revalidating just the d_inode(dentry)
* when we don't really care about the dentry name. This is called when a
@@ -2501,15 +2525,12 @@ int nfs_unlink(struct inode *dir, struct dentry *dentry)
spin_unlock(&dentry->d_lock);
goto out;
}
- /* old devname */
- kfree(dentry->d_fsdata);
- dentry->d_fsdata = NFS_FSDATA_BLOCKED;
+ block_revalidate(dentry);
spin_unlock(&dentry->d_lock);
error = nfs_safe_remove(dentry);
nfs_dentry_remove_handle_error(dir, dentry, error);
- dentry->d_fsdata = NULL;
- wake_up_var(&dentry->d_fsdata);
+ unblock_revalidate(dentry);
out:
trace_nfs_unlink_exit(dir, dentry, error);
return error;
@@ -2616,8 +2637,7 @@ nfs_unblock_rename(struct rpc_task *task, struct nfs_renamedata *data)
{
struct dentry *new_dentry = data->new_dentry;
- new_dentry->d_fsdata = NULL;
- wake_up_var(&new_dentry->d_fsdata);
+ unblock_revalidate(new_dentry);
}
/*
@@ -2679,11 +2699,6 @@ int nfs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
if (WARN_ON(new_dentry->d_flags & DCACHE_NFSFS_RENAMED) ||
WARN_ON(new_dentry->d_fsdata == NFS_FSDATA_BLOCKED))
goto out;
- if (new_dentry->d_fsdata) {
- /* old devname */
- kfree(new_dentry->d_fsdata);
- new_dentry->d_fsdata = NULL;
- }
spin_lock(&new_dentry->d_lock);
if (d_count(new_dentry) > 2) {
@@ -2705,7 +2720,7 @@ int nfs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
new_dentry = dentry;
new_inode = NULL;
} else {
- new_dentry->d_fsdata = NFS_FSDATA_BLOCKED;
+ block_revalidate(new_dentry);
must_unblock = true;
spin_unlock(&new_dentry->d_lock);
}
@@ -2717,6 +2732,8 @@ int nfs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
task = nfs_async_rename(old_dir, new_dir, old_dentry, new_dentry,
must_unblock ? nfs_unblock_rename : NULL);
if (IS_ERR(task)) {
+ if (must_unblock)
+ unblock_revalidate(new_dentry);
error = PTR_ERR(task);
goto out;
}
--
2.44.0