From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from neil.brown.name (neil.brown.name [103.29.64.221]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AFF0012CDAE for ; Wed, 30 Apr 2025 04:05:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=103.29.64.221 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745985904; cv=none; b=IGeJHLRjAaN4FzYjUXmTB9S9rY4sSpJLDd3LsXYpi0nbyra4uwlb6INWRSEveUrbLNUHJ76mnkkoEbCtCy5+voDmYdpaCURueq1CBQRpGKrSUEAD9II8vsVp4y8EkMPu5X4QeEvO2JsJm9aUY+35DbFNZTbJw00q2Is61vqf9S0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745985904; c=relaxed/simple; bh=TFA6FwLzXEXDm2Y3Q5lpcIDe2RYgp5hcJI3rrp4uipU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BIUTXAgY8A+Z40N2pkfHh501eS2RR6rHMh0BJLIfdKhTIreH4KvajZkNVwRWR5PiPeUvAapuMKGVCnXjLNFSi84NtXmQQ7QIkF0p6YNcELP1jDA/dHIoaUCkFjeSduH19zlr3hYsD6N9TwWGGz4Uwt0aAjYdbQPvgrTGoITBEmM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=brown.name; spf=pass smtp.mailfrom=neil.brown.name; arc=none smtp.client-ip=103.29.64.221 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=brown.name Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=neil.brown.name Received: from 196.186.233.220.static.exetel.com.au ([220.233.186.196] helo=home.neil.brown.name) by neil.brown.name with esmtp (Exim 4.95) (envelope-from ) id 1u9ygo-005EZ1-W9; Wed, 30 Apr 2025 04:04:55 +0000 From: NeilBrown To: Trond Myklebust , Anna Schumaker , Mike Snitzer , =?UTF-8?q?Pali=20Roh=C3=A1r?= , Vincent Mailhol Cc: Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org Subject: [PATCH 4/6] nfs_localio: change nfsd_file_put_local() to take a pointer to __rcu struct Date: Wed, 30 Apr 2025 14:01:14 +1000 Message-ID: <20250430040429.2743921-5-neil@brown.name> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250430040429.2743921-1-neil@brown.name> References: <20250430040429.2743921-1-neil@brown.name> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Instead of calling rcu_dereference() before nfsd_file_put_local(), we now pass a pointer to an __rcu value and call rcu_dereference() inside that function. Where rcu_dereference() is currently called the internals of "struct nfsd_file" are not known and that causes older compilers such as gcc-8 to complain. In some cases we have a __kernel (aka normal) pointer not an __rcu pointer so we need to cast it to __rcu first. This is strictly a weakening so no information is lost. Somewhat surprisingly, this cast is accepted by gcc-8. Also change nfs_to_nfsd_file_put_local() to handle receiving a NULL pointer, as that makes some callers a bit simpler. Reported-by: Pali Rohár Reported-by: Vincent Mailhol Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client") Signed-off-by: NeilBrown --- fs/nfs/localio.c | 9 ++++++++- fs/nfs_common/nfslocalio.c | 14 ++++++-------- fs/nfsd/filecache.c | 3 ++- fs/nfsd/filecache.h | 2 +- include/linux/nfslocalio.h | 11 ++++++++--- 5 files changed, 25 insertions(+), 14 deletions(-) diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c index 030a54c8c9d8..157f5dd0ab22 100644 --- a/fs/nfs/localio.c +++ b/fs/nfs/localio.c @@ -207,8 +207,15 @@ void nfs_local_probe_async(struct nfs_client *clp) } EXPORT_SYMBOL_GPL(nfs_local_probe_async); -static inline void nfs_local_file_put(struct nfsd_file *nf) +static inline void nfs_local_file_put(struct nfsd_file *localio) { + /* nfs_to_nfsd_file_put_local() expects an __rcu pointer + * but we have a __kernel pointer. It is always safe + * to cast a __kernel pointer to an __rcu pointer + * because the cast only weakens what is known about the pointer. + */ + struct nfsd_file __rcu *nf = (struct nfsd_file __rcu*) localio; + nfs_to_nfsd_file_put_local(nf); } diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c index d9e2f65912ef..cbf3e38443f9 100644 --- a/fs/nfs_common/nfslocalio.c +++ b/fs/nfs_common/nfslocalio.c @@ -273,8 +273,8 @@ EXPORT_SYMBOL_GPL(nfs_open_local_fh); void nfs_close_local_fh(struct nfs_file_localio *nfl) { - struct nfsd_file *ro_nf = NULL; - struct nfsd_file *rw_nf = NULL; + struct nfsd_file __rcu *ro_nf; + struct nfsd_file __rcu *rw_nf; nfs_uuid_t *nfs_uuid; rcu_read_lock(); @@ -285,8 +285,8 @@ void nfs_close_local_fh(struct nfs_file_localio *nfl) return; } - ro_nf = unrcu_pointer(xchg(&nfl->ro_file, NULL)); - rw_nf = unrcu_pointer(xchg(&nfl->rw_file, NULL)); + ro_nf = xchg(&nfl->ro_file, RCU_INITIALIZER(NULL)); + rw_nf = xchg(&nfl->rw_file, RCU_INITIALIZER(NULL)); spin_lock(&nfs_uuid->lock); /* Remove nfl from nfs_uuid->files list */ @@ -298,10 +298,8 @@ void nfs_close_local_fh(struct nfs_file_localio *nfl) */ RCU_INIT_POINTER(nfl->nfs_uuid, NULL); - if (ro_nf) - nfs_to_nfsd_file_put_local(ro_nf); - if (rw_nf) - nfs_to_nfsd_file_put_local(rw_nf); + nfs_to_nfsd_file_put_local(ro_nf); + nfs_to_nfsd_file_put_local(rw_nf); return; } EXPORT_SYMBOL_GPL(nfs_close_local_fh); diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index 473697278d8f..e1fdc8e2740f 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -378,8 +378,9 @@ nfsd_file_put(struct nfsd_file *nf) * the reference of the nfsd_file. */ struct net * -nfsd_file_put_local(struct nfsd_file *nf) +nfsd_file_put_local(struct nfsd_file __rcu *nf_rcu) { + struct nfsd_file *nf = rcu_dereference(nf_rcu); struct net *net = nf->nf_net; nfsd_file_put(nf); diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h index cd02f91aaef1..e433ccbc31dc 100644 --- a/fs/nfsd/filecache.h +++ b/fs/nfsd/filecache.h @@ -62,7 +62,7 @@ void nfsd_file_cache_shutdown(void); int nfsd_file_cache_start_net(struct net *net); void nfsd_file_cache_shutdown_net(struct net *net); void nfsd_file_put(struct nfsd_file *nf); -struct net *nfsd_file_put_local(struct nfsd_file *nf); +struct net *nfsd_file_put_local(struct nfsd_file __rcu *nf); struct nfsd_file *nfsd_file_get_local(struct nfsd_file *nf); struct nfsd_file *nfsd_file_get(struct nfsd_file *nf); struct file *nfsd_file_file(struct nfsd_file *nf); diff --git a/include/linux/nfslocalio.h b/include/linux/nfslocalio.h index e6cd6ec447f5..e53fd61d0f8b 100644 --- a/include/linux/nfslocalio.h +++ b/include/linux/nfslocalio.h @@ -62,7 +62,7 @@ struct nfsd_localio_operations { const struct nfs_fh *, struct nfsd_file __rcu **pnf, const fmode_t); - struct net *(*nfsd_file_put_local)(struct nfsd_file *); + struct net *(*nfsd_file_put_local)(struct nfsd_file __rcu *); struct nfsd_file *(*nfsd_file_get_local)(struct nfsd_file *); struct file *(*nfsd_file_file)(struct nfsd_file *); } ____cacheline_aligned; @@ -88,14 +88,19 @@ static inline void nfs_to_nfsd_net_put(struct net *net) rcu_read_unlock(); } -static inline void nfs_to_nfsd_file_put_local(struct nfsd_file *localio) +static inline void nfs_to_nfsd_file_put_local(struct nfsd_file __rcu *localio) { /* * Must not hold RCU otherwise nfsd_file_put() can easily trigger: * "Voluntary context switch within RCU read-side critical section!" * by scheduling deep in underlying filesystem (e.g. XFS). */ - struct net *net = nfs_to->nfsd_file_put_local(localio); + struct net *net; + + if (!localio) + return; + + net = nfs_to->nfsd_file_put_local(localio); nfs_to_nfsd_net_put(net); } -- 2.49.0