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From:   =?iso-2022-jp?B?TUlOT1VSQSBNYWtvdG8gLyAbJEJMJzE6GyhCIBskQj8/GyhC?= 
        <minoura@valinux.co.jp>
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Hiroshi Shimamoto <h-shimamoto@nec.com>
Subject: Re: [PATCH v3] SUNRPC: ensure the matching upcall is in-flight upon downcall
References: <20221212060354.3359432-1-minoura@valinux.co.jp>
        <9536769A-A66F-47F2-8EA9-C4FAD51809F9@hammerspace.com>
Date:   Tue, 13 Dec 2022 09:32:36 +0900
In-Reply-To: <9536769A-A66F-47F2-8EA9-C4FAD51809F9@hammerspace.com> (Trond
        Myklebust's message of "Mon, 12 Dec 2022 15:14:49 +0000")
Message-ID: <kk51qp4b0t7.fsf@brer.local.valinux.co.jp>
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Thank you for your comment!

> > On Dec 12, 2022, at 01:03, minoura <minoura@valinux.co.jp> wrote:
> > 
> > From: minoura makoto <minoura@valinux.co.jp>
> > 
> > Commit 9130b8dbc6ac ("SUNRPC: allow for upcalls for the same uid
> > but different gss service") introduced `auth` argument to
> > __gss_find_upcall(), but in gss_pipe_downcall() it was left as NULL
> > since it (and auth->service) was not (yet) determined.
> > 
> > When multiple upcalls with the same uid and different service are
> > ongoing, it could happen that __gss_find_upcall(), which returns the
> > first match found in the pipe->in_downcall list, could not find the
> > correct gss_msg corresponding to the downcall we are looking for.
> > Moreover, it might return a msg which is not sent to rpc.gssd yet.
> > 
> > We could see mount.nfs process hung in D state with multiple mount.nfs
> > are executed in parallel.  The call trace below is of CentOS 7.9
> > kernel-3.10.0-1160.24.1.el7.x86_64 but we observed the same hang w/
> > elrepo kernel-ml-6.0.7-1.el7.
> > 
> > PID: 71258  TASK: ffff91ebd4be0000  CPU: 36  COMMAND: "mount.nfs"
> > #0 [ffff9203ca3234f8] __schedule at ffffffffa3b8899f
> > #1 [ffff9203ca323580] schedule at ffffffffa3b88eb9
> > #2 [ffff9203ca323590] gss_cred_init at ffffffffc0355818 [auth_rpcgss]
> > #3 [ffff9203ca323658] rpcauth_lookup_credcache at ffffffffc0421ebc [sunrpc]
> > #4 [ffff9203ca3236d8] gss_lookup_cred at ffffffffc0353633 [auth_rpcgss]
> > #5 [ffff9203ca3236e8] rpcauth_lookupcred at ffffffffc0421581 [sunrpc]
> > #6 [ffff9203ca323740] rpcauth_refreshcred at ffffffffc04223d3 [sunrpc]
> > #7 [ffff9203ca3237a0] call_refresh at ffffffffc04103dc [sunrpc]
> > #8 [ffff9203ca3237b8] __rpc_execute at ffffffffc041e1c9 [sunrpc]
> > #9 [ffff9203ca323820] rpc_execute at ffffffffc0420a48 [sunrpc]
> > 
> > The scenario is like this. Let's say there are two upcalls for
> > services A and B, A -> B in pipe->in_downcall, B -> A in pipe->pipe.
> > 
> > When rpc.gssd reads pipe to get the upcall msg corresponding to
> > service B from pipe->pipe and then writes the response, in
> > gss_pipe_downcall the msg corresponding to service A will be picked
> > because only uid is used to find the msg and it is before the one for
> > B in pipe->in_downcall.  And the process waiting for the msg
> > corresponding to service A will be woken up.
> > 
> > Actual scheduing of that process might be after rpc.gssd processes the
> > next msg.  In rpc_pipe_generic_upcall it clears msg->errno (for A).
> > The process is scheduled to see gss_msg->ctx == NULL and
> > gss_msg->msg.errno == 0, therefore it cannot break the loop in
> > gss_create_upcall and is never woken up after that.
> > 
> > This patch adds a simple check to ensure that a msg which is not
> > sent to rpc.gssd yet is not chosen as the matching upcall upon
> > receiving a downcall.
> > 
> > Fixes: Commit 9130b8dbc6ac ("SUNRPC: allow for upcalls for the same uid but different gss service")
> > Signed-off-by: minoura makoto <minoura@valinux.co.jp>
> > Signed-off-by: Hiroshi Shimamoto <h-shimamoto@nec.com>
> > Tested-by: Hiroshi Shimamoto <h-shimamoto@nec.com>
> > Cc: Trond Myklebust <trondmy@hammerspace.com>
> > ---
> > v2: use gss_release_msg instead of refcount_dec in fatal_signal_pending case
> > v3: just ensure the msg is already sent instead of serialization (based on Trond's advice)
> > ---
> > include/linux/sunrpc/rpc_pipe_fs.h |  5 +++++
> > net/sunrpc/auth_gss/auth_gss.c     | 19 +++++++++++++++++--
> > 2 files changed, 22 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/sunrpc/rpc_pipe_fs.h b/include/linux/sunrpc/rpc_pipe_fs.h
> > index cd188a527d16..6a29682cb857 100644
> > --- a/include/linux/sunrpc/rpc_pipe_fs.h
> > +++ b/include/linux/sunrpc/rpc_pipe_fs.h
> > @@ -92,6 +92,11 @@ extern ssize_t rpc_pipe_generic_upcall(struct file *, struct rpc_pipe_msg *,
> >       char __user *, size_t);
> > extern int rpc_queue_upcall(struct rpc_pipe *, struct rpc_pipe_msg *);
> > 
> > +/* returns true if the msg is in-flight, i.e., already eaten by the peer */
> > +static inline bool rpc_msg_is_inflight(struct rpc_pipe_msg *msg) {

> Nit: please make that a ‘const struct rpc_pipe_msg *’ argument.

Sure.

> > + return (msg->copied != 0 && list_empty(&msg->list));
> > +}
> > +
> > struct rpc_clnt;
> > extern struct dentry *rpc_create_client_dir(struct dentry *, const char *, struct rpc_clnt *);
> > extern int rpc_remove_client_dir(struct rpc_clnt *);
> > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> > index 7bb247c51e2f..51b67ebe09bf 100644
> > --- a/net/sunrpc/auth_gss/auth_gss.c
> > +++ b/net/sunrpc/auth_gss/auth_gss.c
> > @@ -302,7 +302,7 @@ __gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid, const struct gss_auth *auth
> > list_for_each_entry(pos, &pipe->in_downcall, list) {
> > if (!uid_eq(pos->uid, uid))
> > continue;
> > - if (auth && pos->auth->service != auth->service)
> > + if (pos->auth->service != auth->service)
> > continue;
> > refcount_inc(&pos->count);
> > return pos;
> > @@ -686,6 +686,21 @@ gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred)
> > return err;
> > }
> > 
> > +static struct gss_upcall_msg *
> > +gss_find_matching_upcall(struct rpc_pipe *pipe, kuid_t uid)

> Could we please call this ‘gss_find_downcall()’ in order to clarify the use case?

Right, it's a downcall here.  Will revise the patch.

> > +{
> > + struct gss_upcall_msg *pos;
> > + list_for_each_entry(pos, &pipe->in_downcall, list) {
> > + if (!uid_eq(pos->uid, uid))
> > + continue;
> > + if (!rpc_msg_is_inflight(&pos->msg))
> > + continue;
> > + refcount_inc(&pos->count);
> > + return pos;
> > + }
> > + return NULL;
> > +}
> > +
> > #define MSG_BUF_MAXSIZE 1024
> > 
> > static ssize_t
> > @@ -732,7 +747,7 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
> > err = -ENOENT;
> > /* Find a matching upcall */
> > spin_lock(&pipe->lock);
> > - gss_msg = __gss_find_upcall(pipe, uid, NULL);
> > + gss_msg = gss_find_matching_upcall(pipe, uid);
> > if (gss_msg == NULL) {
> > spin_unlock(&pipe->lock);
> > goto err_put_ctx;
> > -- 
> > 2.25.1
> > 

> Otherwise, this looks great.

> _________________________________
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com