> On Jan 5, 2023, at 6:23 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> Commit fb70bf124b05 ("NFSD: Instantiate a struct file when creating a
> regular NFSv4 file") added the ability to cache an open fd over a
> compound. There are a couple of problems with the way this currently
> works:
>
> It's racy, as a newly-created nfsd_file can end up with its PENDING bit
> cleared while the nf is hashed, and the nf_file pointer is still zeroed
> out. Other tasks can find it in this state and they expect to see a
> valid nf_file, and can oops if nf_file is NULL.
>
> Also, there is no guarantee that we'll end up creating a new nfsd_file
> if one is already in the hash. If an extant entry is in the hash with a
> valid nf_file, nfs4_get_vfs_file will clobber its nf_file pointer with
> the value of op_file and the old nf_file will leak.
>
> Fix both issues by changing nfsd_file_acquire to take an optional file
> pointer. If one is present when this is called, we'll take a new
> reference to it instead of trying to open the file. If the nfsd_file
> already has a valid nf_file, we'll just ignore the optional file and
> pass the nfsd_file back as-is.
>
> Also rework the tracepoints a bit to allow for a cached open variant,
> and don't try to avoid counting acquisitions in the case where we
> already have a cached open file.
>
> Cc: Trond Myklebust <trondmy@xxxxxxxxxxxxxxx>
> Reported-by: Stanislav Saner <ssaner@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/nfsd/filecache.c | 49 ++++++++++++++----------------------------
> fs/nfsd/filecache.h | 5 ++---
> fs/nfsd/nfs4proc.c | 2 +-
> fs/nfsd/nfs4state.c | 20 ++++++-----------
> fs/nfsd/trace.h | 52 ++++++++++++---------------------------------
> 5 files changed, 38 insertions(+), 90 deletions(-)
>
> v2: rebased directly onto current master branch to fix up some
> contextual conflicts
Hi Jeff-
The basic race is that nf_file must be filled in before the PENDING
bit is cleared. Got it.
Seems like -rc fodder, and needs a Fixes: tag.
However, I'd prefer to keep the synopses of nfsd_file_acquire() and
nfsd_file_acquire_gc() identical. nfs4_get_vfs_file() is the one
spot that needs this special behavior, so it should continue to
call nfsd_file_create(), or something like it. How about one of:
nfsd_file_acquire2
nfsd_file_acquire_create
nfsd_file_acquire_cached
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 45b2c9e3f636..6674a86e1917 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -1071,8 +1071,8 @@ nfsd_file_is_cached(struct inode *inode)
>
> static __be32
> nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> - unsigned int may_flags, struct nfsd_file **pnf,
> - bool open, bool want_gc)
> + unsigned int may_flags, struct file *file,
> + struct nfsd_file **pnf, bool want_gc)
> {
> struct nfsd_file_lookup_key key = {
> .type = NFSD_FILE_KEY_FULL,
> @@ -1147,8 +1147,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> status = nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_flags));
> out:
> if (status == nfs_ok) {
> - if (open)
> - this_cpu_inc(nfsd_file_acquisitions);
> + this_cpu_inc(nfsd_file_acquisitions);
> *pnf = nf;
> } else {
> if (refcount_dec_and_test(&nf->nf_ref))
> @@ -1158,20 +1157,23 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
>
> out_status:
> put_cred(key.cred);
> - if (open)
> - trace_nfsd_file_acquire(rqstp, key.inode, may_flags, nf, status);
> + trace_nfsd_file_acquire(rqstp, key.inode, may_flags, nf, status);
> return status;
>
> open_file:
> trace_nfsd_file_alloc(nf);
> nf->nf_mark = nfsd_file_mark_find_or_create(nf, key.inode);
> if (nf->nf_mark) {
> - if (open) {
> + if (file) {
> + get_file(file);
> + nf->nf_file = file;
> + status = nfs_ok;
> + trace_nfsd_file_open_cached(nf, status);
> + } else {
> status = nfsd_open_verified(rqstp, fhp, may_flags,
> &nf->nf_file);
> trace_nfsd_file_open(nf, status);
> - } else
> - status = nfs_ok;
> + }
> } else
> status = nfserr_jukebox;
> /*
> @@ -1207,7 +1209,7 @@ __be32
> nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
> unsigned int may_flags, struct nfsd_file **pnf)
> {
> - return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, true, true);
> + return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, true);
> }
>
> /**
> @@ -1215,6 +1217,7 @@ nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
> * @rqstp: the RPC transaction being executed
> * @fhp: the NFS filehandle of the file to be opened
> * @may_flags: NFSD_MAY_ settings for the file
> + * @file: cached, already-open file (may be NULL)
> * @pnf: OUT: new or found "struct nfsd_file" object
> *
> * The nfsd_file_object returned by this API is reference-counted
> @@ -1226,30 +1229,10 @@ nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
> */
> __be32
> nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> - unsigned int may_flags, struct nfsd_file **pnf)
> -{
> - return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, true, false);
> -}
> -
> -/**
> - * nfsd_file_create - Get a struct nfsd_file, do not open
> - * @rqstp: the RPC transaction being executed
> - * @fhp: the NFS filehandle of the file just created
> - * @may_flags: NFSD_MAY_ settings for the file
> - * @pnf: OUT: new or found "struct nfsd_file" object
> - *
> - * The nfsd_file_object returned by this API is reference-counted
> - * but not garbage-collected. The object is released immediately
> - * one RCU grace period after the final nfsd_file_put().
> - *
> - * Returns nfs_ok and sets @pnf on success; otherwise an nfsstat in
> - * network byte order is returned.
> - */
> -__be32
> -nfsd_file_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> - unsigned int may_flags, struct nfsd_file **pnf)
> + unsigned int may_flags, struct file *file,
> + struct nfsd_file **pnf)
> {
> - return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, false, false);
> + return nfsd_file_do_acquire(rqstp, fhp, may_flags, file, pnf, false);
> }
>
> /*
> diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> index b7efb2c3ddb1..ef0083cd4ea9 100644
> --- a/fs/nfsd/filecache.h
> +++ b/fs/nfsd/filecache.h
> @@ -59,8 +59,7 @@ bool nfsd_file_is_cached(struct inode *inode);
> __be32 nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
> unsigned int may_flags, struct nfsd_file **nfp);
> __be32 nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> - unsigned int may_flags, struct nfsd_file **nfp);
> -__be32 nfsd_file_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> - unsigned int may_flags, struct nfsd_file **nfp);
> + unsigned int may_flags, struct file *file,
> + struct nfsd_file **nfp);
> int nfsd_file_cache_stats_show(struct seq_file *m, void *v);
> #endif /* _FS_NFSD_FILECACHE_H */
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index bd880d55f565..6b09cdd4b067 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -735,7 +735,7 @@ nfsd4_commit(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> __be32 status;
>
> status = nfsd_file_acquire(rqstp, &cstate->current_fh, NFSD_MAY_WRITE |
> - NFSD_MAY_NOT_BREAK_LEASE, &nf);
> + NFSD_MAY_NOT_BREAK_LEASE, NULL, &nf);
> if (status != nfs_ok)
> return status;
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 7b2ee535ade8..b68238024e49 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -5262,18 +5262,10 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> if (!fp->fi_fds[oflag]) {
> spin_unlock(&fp->fi_lock);
>
> - if (!open->op_filp) {
> - status = nfsd_file_acquire(rqstp, cur_fh, access, &nf);
> - if (status != nfs_ok)
> - goto out_put_access;
> - } else {
> - status = nfsd_file_create(rqstp, cur_fh, access, &nf);
> - if (status != nfs_ok)
> - goto out_put_access;
> - nf->nf_file = open->op_filp;
> - open->op_filp = NULL;
> - trace_nfsd_file_create(rqstp, access, nf);
> - }
> + status = nfsd_file_acquire(rqstp, cur_fh, access,
> + open->op_filp, &nf);
> + if (status != nfs_ok)
> + goto out_put_access;
>
> spin_lock(&fp->fi_lock);
> if (!fp->fi_fds[oflag]) {
> @@ -6472,7 +6464,7 @@ nfs4_check_file(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfs4_stid *s,
> goto out;
> }
> } else {
> - status = nfsd_file_acquire(rqstp, fhp, acc, &nf);
> + status = nfsd_file_acquire(rqstp, fhp, acc, NULL, &nf);
> if (status)
> return status;
> }
> @@ -7644,7 +7636,7 @@ static __be32 nfsd_test_lock(struct svc_rqst *rqstp, struct svc_fh *fhp, struct
> struct inode *inode;
> __be32 err;
>
> - err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_READ, &nf);
> + err = nfsd_file_acquire(rqstp, fhp, NFSD_MAY_READ, NULL, &nf);
> if (err)
> return err;
> inode = fhp->fh_dentry->d_inode;
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index c852ae8eaf37..7c6cbc37c8c9 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -981,43 +981,6 @@ TRACE_EVENT(nfsd_file_acquire,
> )
> );
>
> -TRACE_EVENT(nfsd_file_create,
> - TP_PROTO(
> - const struct svc_rqst *rqstp,
> - unsigned int may_flags,
> - const struct nfsd_file *nf
> - ),
> -
> - TP_ARGS(rqstp, may_flags, nf),
> -
> - TP_STRUCT__entry(
> - __field(const void *, nf_inode)
> - __field(const void *, nf_file)
> - __field(unsigned long, may_flags)
> - __field(unsigned long, nf_flags)
> - __field(unsigned long, nf_may)
> - __field(unsigned int, nf_ref)
> - __field(u32, xid)
> - ),
> -
> - TP_fast_assign(
> - __entry->nf_inode = nf->nf_inode;
> - __entry->nf_file = nf->nf_file;
> - __entry->may_flags = may_flags;
> - __entry->nf_flags = nf->nf_flags;
> - __entry->nf_may = nf->nf_may;
> - __entry->nf_ref = refcount_read(&nf->nf_ref);
> - __entry->xid = be32_to_cpu(rqstp->rq_xid);
> - ),
> -
> - TP_printk("xid=0x%x inode=%p may_flags=%s ref=%u nf_flags=%s nf_may=%s nf_file=%p",
> - __entry->xid, __entry->nf_inode,
> - show_nfsd_may_flags(__entry->may_flags),
> - __entry->nf_ref, show_nf_flags(__entry->nf_flags),
> - show_nfsd_may_flags(__entry->nf_may), __entry->nf_file
> - )
> -);
> -
> TRACE_EVENT(nfsd_file_insert_err,
> TP_PROTO(
> const struct svc_rqst *rqstp,
> @@ -1079,8 +1042,8 @@ TRACE_EVENT(nfsd_file_cons_err,
> )
> );
>
> -TRACE_EVENT(nfsd_file_open,
> - TP_PROTO(struct nfsd_file *nf, __be32 status),
> +DECLARE_EVENT_CLASS(nfsd_file_open_class,
> + TP_PROTO(const struct nfsd_file *nf, __be32 status),
> TP_ARGS(nf, status),
> TP_STRUCT__entry(
> __field(void *, nf_inode) /* cannot be dereferenced */
> @@ -1104,6 +1067,17 @@ TRACE_EVENT(nfsd_file_open,
> __entry->nf_file)
> )
>
> +#define DEFINE_NFSD_FILE_OPEN_EVENT(name) \
> +DEFINE_EVENT(nfsd_file_open_class, name, \
> + TP_PROTO( \
> + const struct nfsd_file *nf, \
> + __be32 status \
> + ), \
> + TP_ARGS(nf, status))
> +
> +DEFINE_NFSD_FILE_OPEN_EVENT(nfsd_file_open);
> +DEFINE_NFSD_FILE_OPEN_EVENT(nfsd_file_open_cached);
> +
> TRACE_EVENT(nfsd_file_is_cached,
> TP_PROTO(
> const struct inode *inode,
> --
> 2.39.0
>
--
Chuck Lever
