> Subject: [PATCH] SUNRPC: serialize gss upcalls for the same uid
>
> 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 due
> to two reasons:
>
> - the order of the msgs in pipe->in_downcall and those in pipe->pipe
> (that is, the order of the upcalls sent to rpc.gssd) might be
> different because pipe->lock is dropped between adding one to each
> list.
> - rpc.gssd uses threads to write responses, which means we cannot
> guarantee the order of responses.
>
> 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 introduces wait and retry at gss_add_msg() to serialize
> when requests with the same uid but different service comes.
>
> Fixes: Commit 9130b8dbc6ac ("SUNRPC: allow for upcalls for the same uid but different gss service")
> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@xxxxxxx>
> Signed-off-by: minoura makoto <minoura@xxxxxxxxxxxxx>
>
> ---
> net/sunrpc/auth_gss/auth_gss.c | 31 +++++++++++++++++++++++++------
> 1 file changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> index 7bb247c51e2f..696f8c22c594 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -296,14 +296,12 @@ gss_release_msg(struct gss_upcall_msg *gss_msg)
> }
>
> static struct gss_upcall_msg *
> -__gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid, const struct gss_auth *auth)
> +__gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid)
> {
> struct gss_upcall_msg *pos;
> list_for_each_entry(pos, &pipe->in_downcall, list) {
> if (!uid_eq(pos->uid, uid))
> continue;
> - if (auth && pos->auth->service != auth->service)
> - continue;
> refcount_inc(&pos->count);
> return pos;
> }
> @@ -319,14 +317,31 @@ gss_add_msg(struct gss_upcall_msg *gss_msg)
> {
> struct rpc_pipe *pipe = gss_msg->pipe;
> struct gss_upcall_msg *old;
> + DEFINE_WAIT(wait);
>
> spin_lock(&pipe->lock);
> - old = __gss_find_upcall(pipe, gss_msg->uid, gss_msg->auth);
> +retry:
> + old = __gss_find_upcall(pipe, gss_msg->uid);
> if (old == NULL) {
> refcount_inc(&gss_msg->count);
> list_add(&gss_msg->list, &pipe->in_downcall);
> - } else
> + } else {
> + if (old->auth->service != gss_msg->auth->service) {
> + prepare_to_wait(&old->waitqueue, &wait, TASK_KILLABLE);
> + spin_unlock(&pipe->lock);
> + if (fatal_signal_pending(current)) {
> + finish_wait(&old->waitqueue, &wait);
> + refcount_dec(&old->count);
Should we use gss_release_msg(old) ?
It might be the last decrement of the count and lead to resource leak.
Thanks,
Hiroshi
> + return ERR_PTR(-ERESTARTSYS);
> + }
> + schedule();
> + finish_wait(&old->waitqueue, &wait);
> + gss_release_msg(old);
> + spin_lock(&pipe->lock);
> + goto retry;
> + }
> gss_msg = old;
> + }
> spin_unlock(&pipe->lock);
> return gss_msg;
> }
> @@ -554,6 +569,10 @@ gss_setup_upcall(struct gss_auth *gss_auth, struct rpc_cred *cred)
> if (IS_ERR(gss_new))
> return gss_new;
> gss_msg = gss_add_msg(gss_new);
> + if (IS_ERR(gss_msg)) {
> + gss_release_msg(gss_new);
> + return gss_msg;
> + }
> if (gss_msg == gss_new) {
> int res;
> refcount_inc(&gss_msg->count);
> @@ -732,7 +751,7 @@ 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_upcall(pipe, uid);
> if (gss_msg == NULL) {
> spin_unlock(&pipe->lock);
> goto err_put_ctx;
> --
> 2.25.1
