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

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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>
This commit is contained in:
Jeff Layton 2020-11-30 17:03:16 -05:00 committed by Chuck Lever
parent ba5e8187c5
commit 7f84b488f9
4 changed files with 26 additions and 10 deletions
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13
Documentation/filesystems/nfs/exporting.rst
View File

@ -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.

2
fs/nfs/export.c
View File

@ -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,
};

16
fs/nfsd/vfs.c
View File

@ -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);

5
include/linux/exportfs.h
View File

@ -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;
};