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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Jeff Layton <jlayton@kernel.org>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Wang Yugui <wangyugui@e16-tech.com>,
        Trond Myklebust <trondmy@hammerspace.com>,
        Stanislav Saner <ssaner@redhat.com>
Subject: Re: [PATCH] nfsd: fix handling of cached open files in nfsd4_open
 codepath
Thread-Topic: [PATCH] nfsd: fix handling of cached open files in nfsd4_open
 codepath
Thread-Index: AQHZIT++RVF+9Furhk+vRGFbl1gW8q6RrfcA
Date:   Fri, 6 Jan 2023 17:56:42 +0000
Message-ID: <BC8EF64C-3F08-4E10-B562-344FFD1D37B2@oracle.com>
References: <20230105195556.1557555-1-jlayton@kernel.org>
In-Reply-To: <20230105195556.1557555-1-jlayton@kernel.org>
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> On Jan 5, 2023, at 2:55 PM, Jeff Layton <jlayton@kernel.org> wrote:
>=20
> 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:
>=20
> 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.
>=20
> 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.
>=20
> Fix both issues by making a new nfsd_file_acquirei_opened variant that
> takes 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.
>=20
> Also rework the tracepoints a bit to allow for an "opened" variant and
> don't try to avoid counting acquisitions in the case where we already
> have a cached open file.
>=20
> Fixes: fb70bf124b05 ("NFSD: Instantiate a struct file when creating a reg=
ular NFSv4 file")
> Cc: Trond Myklebust <trondmy@hammerspace.com>
> Reported-by: Stanislav Saner <ssaner@redhat.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
> fs/nfsd/filecache.c | 40 ++++++++++++++++++----------------
> fs/nfsd/filecache.h |  5 +++--
> fs/nfsd/nfs4state.c | 16 ++++----------
> fs/nfsd/trace.h     | 52 ++++++++++++---------------------------------
> 4 files changed, 42 insertions(+), 71 deletions(-)
>=20
> v3: add new nfsd_file_acquire_opened variant instead of changing
>    nfsd_file_acquire prototype

Hi Jeff, v3 applied to nfsd's for-rc.


> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 45b2c9e3f636..0ef070349014 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -1071,8 +1071,8 @@ nfsd_file_is_cached(struct inode *inode)
>=20
> 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 =3D {
> 		.type	=3D NFSD_FILE_KEY_FULL,
> @@ -1147,8 +1147,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct=
 svc_fh *fhp,
> 	status =3D nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_f=
lags));
> out:
> 	if (status =3D=3D nfs_ok) {
> -		if (open)
> -			this_cpu_inc(nfsd_file_acquisitions);
> +		this_cpu_inc(nfsd_file_acquisitions);
> 		*pnf =3D nf;
> 	} else {
> 		if (refcount_dec_and_test(&nf->nf_ref))
> @@ -1158,20 +1157,23 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, stru=
ct svc_fh *fhp,
>=20
> 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;
>=20
> open_file:
> 	trace_nfsd_file_alloc(nf);
> 	nf->nf_mark =3D nfsd_file_mark_find_or_create(nf, key.inode);
> 	if (nf->nf_mark) {
> -		if (open) {
> +		if (file) {
> +			get_file(file);
> +			nf->nf_file =3D file;
> +			status =3D nfs_ok;
> +			trace_nfsd_file_opened(nf, status);
> +		} else {
> 			status =3D nfsd_open_verified(rqstp, fhp, may_flags,
> 						    &nf->nf_file);
> 			trace_nfsd_file_open(nf, status);
> -		} else
> -			status =3D nfs_ok;
> +		}
> 	} else
> 		status =3D 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);
> }
>=20
> /**
> @@ -1228,28 +1230,30 @@ __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);
> +	return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, false);
> }
>=20
> /**
> - * nfsd_file_create - Get a struct nfsd_file, do not open
> + * nfsd_file_acquire_opened - Get a struct nfsd_file using existing open=
 file
>  * @rqstp: the RPC transaction being executed
>  * @fhp: the NFS filehandle of the file just created
>  * @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
> - * but not garbage-collected. The object is released immediately
> - * one RCU grace period after the final nfsd_file_put().
> + * Acquire a nfsd_file object that is not GC'ed. If one doesn't already =
exist,
> + * and @file is non-NULL, use it to instantiate a new nfsd_file instead =
of
> + * opening a new one.
>  *
>  * 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)
> +nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *fhp,
> +			 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);
> }
>=20
> /*
> diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> index b7efb2c3ddb1..41516a4263ea 100644
> --- a/fs/nfsd/filecache.h
> +++ b/fs/nfsd/filecache.h
> @@ -60,7 +60,8 @@ __be32 nfsd_file_acquire_gc(struct svc_rqst *rqstp, str=
uct 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);
> +__be32 nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *f=
hp,
> +		  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/nfs4state.c b/fs/nfsd/nfs4state.c
> index 7b2ee535ade8..4809ae0f0138 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);
>=20
> -		if (!open->op_filp) {
> -			status =3D nfsd_file_acquire(rqstp, cur_fh, access, &nf);
> -			if (status !=3D nfs_ok)
> -				goto out_put_access;
> -		} else {
> -			status =3D nfsd_file_create(rqstp, cur_fh, access, &nf);
> -			if (status !=3D nfs_ok)
> -				goto out_put_access;
> -			nf->nf_file =3D open->op_filp;
> -			open->op_filp =3D NULL;
> -			trace_nfsd_file_create(rqstp, access, nf);
> -		}
> +		status =3D nfsd_file_acquire_opened(rqstp, cur_fh, access,
> +						  open->op_filp, &nf);
> +		if (status !=3D nfs_ok)
> +			goto out_put_access;
>=20
> 		spin_lock(&fp->fi_lock);
> 		if (!fp->fi_fds[oflag]) {
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index c852ae8eaf37..8f9c82d9e075 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -981,43 +981,6 @@ TRACE_EVENT(nfsd_file_acquire,
> 	)
> );
>=20
> -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 =3D nf->nf_inode;
> -		__entry->nf_file =3D nf->nf_file;
> -		__entry->may_flags =3D may_flags;
> -		__entry->nf_flags =3D nf->nf_flags;
> -		__entry->nf_may =3D nf->nf_may;
> -		__entry->nf_ref =3D refcount_read(&nf->nf_ref);
> -		__entry->xid =3D be32_to_cpu(rqstp->rq_xid);
> -	),
> -
> -	TP_printk("xid=3D0x%x inode=3D%p may_flags=3D%s ref=3D%u nf_flags=3D%s =
nf_may=3D%s nf_file=3D%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,
> 	)
> );
>=20
> -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)
> )
>=20
> +#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_opened);
> +
> TRACE_EVENT(nfsd_file_is_cached,
> 	TP_PROTO(
> 		const struct inode *inode,
> --=20
> 2.39.0
>=20

--
Chuck Lever