nfsd: close cached files prior to a REMOVE or RENAME that would replace target

It's not uncommon for some workloads to do a bunch of I/O to a file and
delete it just afterward. If knfsd has a cached open file however, then
the file may still be open when the dentry is unlinked. If the
underlying filesystem is nfs, then that could trigger it to do a
sillyrename.

On a REMOVE or RENAME scan the nfsd_file cache for open files that
correspond to the inode, and proactively unhash and put their
references. This should prevent any delete-on-last-close activity from
occurring, solely due to knfsd's open file cache.

This must be done synchronously though so we use the variants that call
flush_delayed_fput. There are deadlock possibilities if you call
flush_delayed_fput while holding locks, however. In the case of
nfsd_rename, we don't even do the lookups of the dentries to be renamed
until we've locked for rename.

Once we've figured out what the target dentry is for a rename, check to
see whether there are cached open files associated with it. If there
are, then unwind all of the locking, close them all, and then reattempt
the rename.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 53 insertions, 9 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 8e2c8f36eba3..84e87772c2b8 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1590,6 +1590,26 @@ out_nfserr:
         goto out_unlock;
 }
 
+static void
+nfsd_close_cached_files(struct dentry *dentry)
+{
+        struct inode *inode = d_inode(dentry);
+
+        if (inode && S_ISREG(inode->i_mode))
+                nfsd_file_close_inode_sync(inode);
+}
+
+static bool
+nfsd_has_cached_files(struct dentry *dentry)
+{
+        bool            ret = false;
+        struct inode *inode = d_inode(dentry);
+
+        if (inode && S_ISREG(inode->i_mode))
+                ret = nfsd_file_is_cached(inode);
+        return ret;
+}
+
 /*
  * Rename a file
  * N.B. After this call _both_ ffhp and tfhp need an fh_put
@@ -1602,6 +1622,7 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         struct inode    *fdir, *tdir;
         __be32          err;
         int             host_err;
+        bool            has_cached = false;
 
         err = fh_verify(rqstp, ffhp, S_IFDIR, NFSD_MAY_REMOVE);
         if (err)
@@ -1620,6 +1641,7 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
                 goto out;
 
+retry:
         host_err = fh_want_write(ffhp);
         if (host_err) {
                 err = nfserrno(host_err);
@@ -1659,11 +1681,16 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
                 goto out_dput_new;
 
-        host_err = vfs_rename(fdir, odentry, tdir, ndentry, NULL, 0);
-        if (!host_err) {
-                host_err = commit_metadata(tfhp);
-                if (!host_err)
-                        host_err = commit_metadata(ffhp);
+        if (nfsd_has_cached_files(ndentry)) {
+                has_cached = true;
+                goto out_dput_old;
+        } else {
+                host_err = vfs_rename(fdir, odentry, tdir, ndentry, NULL, 0);
+                if (!host_err) {
+                        host_err = commit_metadata(tfhp);
+                        if (!host_err)
+                                host_err = commit_metadata(ffhp);
+                }
         }
  out_dput_new:
         dput(ndentry);
@@ -1676,12 +1703,26 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
          * as that would do the wrong thing if the two directories
          * were the same, so again we do it by hand.
          */
-        fill_post_wcc(ffhp);
-        fill_post_wcc(tfhp);
+        if (!has_cached) {
+                fill_post_wcc(ffhp);
+                fill_post_wcc(tfhp);
+        }
         unlock_rename(tdentry, fdentry);
         ffhp->fh_locked = tfhp->fh_locked = false;
         fh_drop_write(ffhp);
 
+        /*
+         * If the target dentry has cached open files, then we need to try to
+         * close them prior to doing the rename. Flushing delayed fput
+         * shouldn't be done with locks held however, so we delay it until this
+         * point and then reattempt the whole shebang.
+         */
+        if (has_cached) {
+                has_cached = false;
+                nfsd_close_cached_files(ndentry);
+                dput(ndentry);
+                goto retry;
+        }
 out:
         return err;
 }
@@ -1728,10 +1769,13 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
         if (!type)
                 type = d_inode(rdentry)->i_mode & S_IFMT;
 
-        if (type != S_IFDIR)
+        if (type != S_IFDIR) {
+                nfsd_close_cached_files(rdentry);
                 host_err = vfs_unlink(dirp, rdentry, NULL);
-        else
+        } else {
                 host_err = vfs_rmdir(dirp, rdentry);
+        }
+
         if (!host_err)
                 host_err = commit_metadata(fhp);
         dput(rdentry);