From: NeilBrown <neilb@suse.de>
Date: Mon, 17 May 2021 09:34:38 +1000
Subject: [PATCH] SUNRPC in case of backlog, hand free slots directly to
waiting task
Git-commit: e877a88d1f069edced4160792f42c2a8e2dba942
Patch-mainline: v5.13
References: bsc#1185428
If sunrpc.tcp_max_slot_table_entries is small and there are tasks
on the backlog queue, then when a request completes it is freed and the
first task on the queue is woken. The expectation is that it will wake
and claim that request. However if it was a sync task and the waiting
process was killed at just that moment, it will wake and NOT claim the
request.
As long as TASK_CONGESTED remains set, requests can only be claimed by
tasks woken from the backlog, and they are woken only as requests are
freed, so when a task doesn't claim a request, no other task can ever
get that request until TASK_CONGESTED is cleared. Each time this
happens the number of available requests is decreased by one.
With a sufficiently high workload and sufficiently low setting of
max_slot (16 in the case where this was seen), TASK_CONGESTED can remain
set for an extended period, and the above scenario (of a process being
killed just as its task was woken) can repeat until no requests can be
allocated. Then traffic stops.
This patch addresses the problem by introducing a positive handover of a
request from a completing task to a backlog task - the request is never
freed when there is a backlog.
When a task is woken it might already have a request attached in which
case it is *not* freed (as with current code) but is initialised (if
needed) and used. If it isn't used it will eventually be freed by
rpc_exit_task(). xprt_release() is enhanced to be able to correctly
release an uninitialised request.
Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: NeilBrown <neilb@suse.com>
---
net/sunrpc/clnt.c | 10 ------
net/sunrpc/xprt.c | 84 +++++++++++++++++++++++++++++++++++-------------------
2 files changed, 55 insertions(+), 39 deletions(-)
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1599,16 +1599,6 @@ call_reserveresult(struct rpc_task *task
return;
}
- /*
- * Even though there was an error, we may have acquired
- * a request slot somehow. Make sure not to leak it.
- */
- if (task->tk_rqstp) {
- printk(KERN_ERR "%s: status=%d, request allocated anyway\n",
- __func__, status);
- xprt_release(task);
- }
-
switch (status) {
case -ENOMEM:
rpc_delay(task, HZ >> 2);
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -71,6 +71,7 @@ static void xprt_connect_status(struct r
static int __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
static void __xprt_put_cong(struct rpc_xprt *, struct rpc_rqst *);
static void xprt_destroy(struct rpc_xprt *xprt);
+static void xprt_request_init(struct rpc_task *task);
static DEFINE_SPINLOCK(xprt_list_lock);
static LIST_HEAD(xprt_list);
@@ -1091,10 +1092,26 @@ static void xprt_add_backlog(struct rpc_
rpc_sleep_on(&xprt->backlog, task, NULL);
}
-static void xprt_wake_up_backlog(struct rpc_xprt *xprt)
+static bool __xprt_set_rq(struct rpc_task *task, void *data)
{
- if (rpc_wake_up_next(&xprt->backlog) == NULL)
+ struct rpc_rqst *req = data;
+
+ if (task->tk_rqstp == NULL) {
+ memset(req, 0, sizeof(*req)); /* mark unused */
+ task->tk_status = -EAGAIN;
+ task->tk_rqstp = req;
+ return true;
+ }
+ return false;
+}
+
+static bool xprt_wake_up_backlog(struct rpc_xprt *xprt, struct rpc_rqst *req)
+{
+ if (rpc_wake_up_first(&xprt->backlog, __xprt_set_rq, req) == NULL) {
clear_bit(XPRT_CONGESTED, &xprt->state);
+ return false;
+ }
+ return true;
}
static bool xprt_throttle_congested(struct rpc_xprt *xprt, struct rpc_task *task)
@@ -1195,11 +1212,11 @@ EXPORT_SYMBOL_GPL(xprt_lock_and_alloc_sl
void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
spin_lock(&xprt->reserve_lock);
- if (!xprt_dynamic_free_slot(xprt, req)) {
+ if (!xprt_wake_up_backlog(xprt, req) &&
+ !xprt_dynamic_free_slot(xprt, req)) {
memset(req, 0, sizeof(*req)); /* mark unused */
list_add(&req->rq_list, &xprt->free);
}
- xprt_wake_up_backlog(xprt);
spin_unlock(&xprt->reserve_lock);
}
EXPORT_SYMBOL_GPL(xprt_free_slot);
@@ -1281,6 +1298,10 @@ xprt_request_init(struct rpc_task *task)
struct rpc_xprt *xprt = task->tk_xprt;
struct rpc_rqst *req = task->tk_rqstp;
+ if (req->rq_task)
+ /* Already initialized */
+ return;
+
INIT_LIST_HEAD(&req->rq_list);
req->rq_timeout = task->tk_client->cl_timeout->to_initval;
req->rq_task = task;
@@ -1343,8 +1364,10 @@ void xprt_retry_reserve(struct rpc_task
struct rpc_xprt *xprt = task->tk_xprt;
task->tk_status = 0;
- if (task->tk_rqstp != NULL)
+ if (task->tk_rqstp != NULL) {
+ xprt_request_init(task);
return;
+ }
task->tk_timeout = 0;
task->tk_status = -EAGAIN;
@@ -1371,31 +1394,34 @@ void xprt_release(struct rpc_task *task)
}
xprt = req->rq_xprt;
- if (task->tk_ops->rpc_count_stats != NULL)
- task->tk_ops->rpc_count_stats(task, task->tk_calldata);
- else if (task->tk_client)
- rpc_count_iostats(task, task->tk_client->cl_metrics);
- spin_lock(&xprt->recv_lock);
- if (!list_empty(&req->rq_list)) {
- list_del_init(&req->rq_list);
- xprt_wait_on_pinned_rqst(req);
- }
- spin_unlock(&xprt->recv_lock);
- spin_lock_bh(&xprt->transport_lock);
- xprt->ops->release_xprt(xprt, task);
- if (xprt->ops->release_request)
- xprt->ops->release_request(task);
- xprt->last_used = jiffies;
- xprt_schedule_autodisconnect(xprt);
- spin_unlock_bh(&xprt->transport_lock);
- if (req->rq_buffer)
- xprt->ops->buf_free(task);
- if (req->rq_cred != NULL)
- put_rpccred(req->rq_cred);
- task->tk_rqstp = NULL;
- if (req->rq_release_snd_buf)
- req->rq_release_snd_buf(req);
+ if (xprt) {
+ if (task->tk_ops->rpc_count_stats != NULL)
+ task->tk_ops->rpc_count_stats(task, task->tk_calldata);
+ else if (task->tk_client)
+ rpc_count_iostats(task, task->tk_client->cl_metrics);
+ spin_lock(&xprt->recv_lock);
+ if (!list_empty(&req->rq_list)) {
+ list_del_init(&req->rq_list);
+ xprt_wait_on_pinned_rqst(req);
+ }
+ spin_unlock(&xprt->recv_lock);
+ spin_lock_bh(&xprt->transport_lock);
+ xprt->ops->release_xprt(xprt, task);
+ if (xprt->ops->release_request)
+ xprt->ops->release_request(task);
+ xprt->last_used = jiffies;
+ xprt_schedule_autodisconnect(xprt);
+ spin_unlock_bh(&xprt->transport_lock);
+ if (req->rq_buffer)
+ xprt->ops->buf_free(task);
+ if (req->rq_cred != NULL)
+ put_rpccred(req->rq_cred);
+ if (req->rq_release_snd_buf)
+ req->rq_release_snd_buf(req);
+ } else
+ xprt = task->tk_xprt;
+ task->tk_rqstp = NULL;
dprintk("RPC: %5u release request %p\n", task->tk_pid, req);
if (likely(!bc_prealloc(req)))
xprt->ops->free_slot(xprt, req);