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.

None of this is really necessary for "typical" filesystems though. It's
mostly of use for NFS, so declare a new export op flag and use that to
determine whether to close the files beforehand.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Lance Shelton <lance.shelton@hammerspace.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/Documentation/filesystems/nfs/exporting.rst b/Documentation/filesystems/nfs/exporting.rst
index 960be64446cb9678ef475a6905688d42c24f74ec..0e98edd353b5f13920ec0837525e371bf16815ee 100644 (file)
--- a/Documentation/filesystems/nfs/exporting.rst
+++ b/Documentation/filesystems/nfs/exporting.rst
@@ -202,3 +202,16 @@ following flags are defined:
     This flag exempts the filesystem from subtree checking and causes
     exportfs to get back an error if it tries to enable subtree checking
     on it.
+
+  EXPORT_OP_CLOSE_BEFORE_UNLINK - always close cached files before unlinking
+    On some exportable filesystems (such as NFS) unlinking a file that
+    is still open can cause a fair bit of extra work. For instance,
+    the NFS client will do a "sillyrename" to ensure that the file
+    sticks around while it's still open. When reexporting, that open
+    file is held by nfsd so we usually end up doing a sillyrename, and
+    then immediately deleting the sillyrenamed file just afterward when
+    the link count actually goes to zero. Sometimes this delete can race
+    with other operations (for instance an rmdir of the parent directory).
+    This flag causes nfsd to close any open files for this inode _before_
+    calling into the vfs to do an unlink or a rename that would replace
+    an existing file.

diff --git a/fs/nfs/export.c b/fs/nfs/export.c
index b9ba306bf912055f946587e557d5c40d7aa4e9e5..5428713af5feedc8d13ab23d93a483bc30653fe0 100644 (file)
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -171,5 +171,5 @@ const struct export_operations nfs_export_ops = {
        .encode_fh = nfs_encode_fh,
        .fh_to_dentry = nfs_fh_to_dentry,
        .get_parent = nfs_get_parent,
-       .flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK,
+       .flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|EXPORT_OP_CLOSE_BEFORE_UNLINK,
 };

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 1ecaceebee1339716c03a24819bbea664aaf79fb..79cba942087e8bbbce4bb03a635c14186ece7397 100644 (file)
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1724,7 +1724,7 @@ 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;
+       bool            close_cached = false;
 
        err = fh_verify(rqstp, ffhp, S_IFDIR, NFSD_MAY_REMOVE);
        if (err)
@@ -1783,8 +1783,9 @@ retry:
        if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
                goto out_dput_new;
 
-       if (nfsd_has_cached_files(ndentry)) {
-               has_cached = true;
+       if ((ndentry->d_sb->s_export_op->flags & EXPORT_OP_CLOSE_BEFORE_UNLINK) &&
+           nfsd_has_cached_files(ndentry)) {
+               close_cached = true;
                goto out_dput_old;
        } else {
                host_err = vfs_rename(fdir, odentry, tdir, ndentry, NULL, 0);
@@ -1805,7 +1806,7 @@ retry:
         * as that would do the wrong thing if the two directories
         * were the same, so again we do it by hand.
         */
-       if (!has_cached) {
+       if (!close_cached) {
                fill_post_wcc(ffhp);
                fill_post_wcc(tfhp);
        }
@@ -1819,8 +1820,8 @@ retry:
         * 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;
+       if (close_cached) {
+               close_cached = false;
                nfsd_close_cached_files(ndentry);
                dput(ndentry);
                goto retry;
@@ -1872,7 +1873,8 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
                type = d_inode(rdentry)->i_mode & S_IFMT;
 
        if (type != S_IFDIR) {
-               nfsd_close_cached_files(rdentry);
+               if (rdentry->d_sb->s_export_op->flags & EXPORT_OP_CLOSE_BEFORE_UNLINK)
+                       nfsd_close_cached_files(rdentry);
                host_err = vfs_unlink(dirp, rdentry, NULL);
        } else {
                host_err = vfs_rmdir(dirp, rdentry);

diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 2fcbab0f6b612fb5f672e25d39a1ced99701075f..d829403ffd3bbb6b74aa00f1efe7ddc707f57260 100644 (file)
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -213,8 +213,9 @@ struct export_operations {
                          bool write, u32 *device_generation);
        int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
                             int nr_iomaps, struct iattr *iattr);
-#define        EXPORT_OP_NOWCC         (0x1)   /* Don't collect wcc data for NFSv3 replies */
-#define        EXPORT_OP_NOSUBTREECHK  (0x2)   /* Subtree checking is not supported! */
+#define        EXPORT_OP_NOWCC                 (0x1) /* don't collect v3 wcc data */
+#define        EXPORT_OP_NOSUBTREECHK          (0x2) /* no subtree checking */
+#define        EXPORT_OP_CLOSE_BEFORE_UNLINK   (0x4) /* close files before unlink */
        unsigned long   flags;
 };