[PATCH 5.10 028/717] RDMA/rtrs-srv: Dont guard the whole __alloc_srv with srv_mutex

Greg Kroah-Hartman
2020-12-28T14:01:17Z

From: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>

[ Upstream commit d715ff8acbd5876549ef2b21b755ed919f40dcc1 ]

The purpose of srv_mutex is to protect srv_list as in put_srv, so no need
to hold it when allocate memory for srv since it could be time consuming.

Otherwise if one machine has limited memory, rsrv_close_work could be
blocked for a longer time due to the mutex is held by get_or_create_srv
since it can't get memory in time.

INFO: task kworker/1:1:27478 blocked for more than 120 seconds.
Tainted: G O 4.14.171-1-storage #4.14.171-1.3~deb9
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/1:1 D 0 27478 2 0x80000000
Workqueue: rtrs_server_wq rtrs_srv_close_work [rtrs_server]
Call Trace:
? __schedule+0x38c/0x7e0
schedule+0x32/0x80
schedule_preempt_disabled+0xa/0x10
__mutex_lock.isra.2+0x25e/0x4d0
? put_srv+0x44/0x100 [rtrs_server]
put_srv+0x44/0x100 [rtrs_server]
rtrs_srv_close_work+0x16c/0x280 [rtrs_server]
process_one_work+0x1c5/0x3c0
worker_thread+0x47/0x3e0
kthread+0xfc/0x130
? trace_event_raw_event_workqueue_execute_start+0xa0/0xa0
? kthread_create_on_node+0x70/0x70
ret_from_fork+0x1f/0x30

Let's move all the logics from __find_srv_and_get and __alloc_srv to
get_or_create_srv, and remove the two functions. Then it should be safe
for multiple processes to access the same srv since it is protected with
srv_mutex.

And since we don't want to allocate chunks with srv_mutex held, let's
check the srv->refcount after get srv because the chunks could not be
allocated yet.

Fixes: 9cb837480424 ("RDMA/rtrs: server: main functionality")
Link: https://lore.kernel.org/r/20201023074353.21946-6-jinpu.wang@cloud.ionos.com
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/infiniband/ulp/rtrs/rtrs-srv.c | 86 +++++++++++---------------
1 file changed, 37 insertions(+), 49 deletions(-)

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv.c b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
index d6f93601712e4..1cb778aff3c59 100644
--- a/drivers/infiniband/ulp/rtrs/rtrs-srv.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
@@ -1328,17 +1328,42 @@ static void rtrs_srv_dev_release(struct device *dev)
kfree(srv);
}

-static struct rtrs_srv *__alloc_srv(struct rtrs_srv_ctx *ctx,
- const uuid_t *paths_uuid)
+static void free_srv(struct rtrs_srv *srv)
+{
+ int i;
+
+ WARN_ON(refcount_read(&srv->refcount));
+ for (i = 0; i < srv->queue_depth; i++)
+ mempool_free(srv->chunks[i], chunk_pool);
+ kfree(srv->chunks);
+ mutex_destroy(&srv->paths_mutex);
+ mutex_destroy(&srv->paths_ev_mutex);
+ /* last put to release the srv structure */
+ put_device(&srv->dev);
+}
+
+static struct rtrs_srv *get_or_create_srv(struct rtrs_srv_ctx *ctx,
+ const uuid_t *paths_uuid)
{
struct rtrs_srv *srv;
int i;

+ mutex_lock(&ctx->srv_mutex);
+ list_for_each_entry(srv, &ctx->srv_list, ctx_list) {
+ if (uuid_equal(&srv->paths_uuid, paths_uuid) &&
+ refcount_inc_not_zero(&srv->refcount)) {
+ mutex_unlock(&ctx->srv_mutex);
+ return srv;
+ }
+ }
+
+ /* need to allocate a new srv */
srv = kzalloc(sizeof(*srv), GFP_KERNEL);
- if (!srv)
+ if (!srv) {
+ mutex_unlock(&ctx->srv_mutex);
return NULL;
+ }

- refcount_set(&srv->refcount, 1);
INIT_LIST_HEAD(&srv->paths_list);
mutex_init(&srv->paths_mutex);
mutex_init(&srv->paths_ev_mutex);
@@ -1347,6 +1372,8 @@ static struct rtrs_srv *__alloc_srv(struct rtrs_srv_ctx *ctx,
srv->ctx = ctx;
device_initialize(&srv->dev);
srv->dev.release = rtrs_srv_dev_release;
+ list_add(&srv->ctx_list, &ctx->srv_list);
+ mutex_unlock(&ctx->srv_mutex);

srv->chunks = kcalloc(srv->queue_depth, sizeof(*srv->chunks),
GFP_KERNEL);
@@ -1358,7 +1385,7 @@ static struct rtrs_srv *__alloc_srv(struct rtrs_srv_ctx *ctx,
if (!srv->chunks[i])
goto err_free_chunks;
}
- list_add(&srv->ctx_list, &ctx->srv_list);
+ refcount_set(&srv->refcount, 1);

return srv;

@@ -1369,52 +1396,9 @@ err_free_chunks:

err_free_srv:
kfree(srv);
-
return NULL;
}

-static void free_srv(struct rtrs_srv *srv)
-{
- int i;
-
- WARN_ON(refcount_read(&srv->refcount));
- for (i = 0; i < srv->queue_depth; i++)
- mempool_free(srv->chunks[i], chunk_pool);
- kfree(srv->chunks);
- mutex_destroy(&srv->paths_mutex);
- mutex_destroy(&srv->paths_ev_mutex);
- /* last put to release the srv structure */
- put_device(&srv->dev);
-}
-
-static inline struct rtrs_srv *__find_srv_and_get(struct rtrs_srv_ctx *ctx,
- const uuid_t *paths_uuid)
-{
- struct rtrs_srv *srv;
-
- list_for_each_entry(srv, &ctx->srv_list, ctx_list) {
- if (uuid_equal(&srv->paths_uuid, paths_uuid) &&
- refcount_inc_not_zero(&srv->refcount))
- return srv;
- }
-
- return NULL;
-}
-
-static struct rtrs_srv *get_or_create_srv(struct rtrs_srv_ctx *ctx,
- const uuid_t *paths_uuid)
-{
- struct rtrs_srv *srv;
-
- mutex_lock(&ctx->srv_mutex);
- srv = __find_srv_and_get(ctx, paths_uuid);
- if (!srv)
- srv = __alloc_srv(ctx, paths_uuid);
- mutex_unlock(&ctx->srv_mutex);
-
- return srv;
-}
-
static void put_srv(struct rtrs_srv *srv)
{
if (refcount_dec_and_test(&srv->refcount)) {
@@ -1813,7 +1797,11 @@ static int rtrs_rdma_connect(struct rdma_cm_id *cm_id,
}
recon_cnt = le16_to_cpu(msg->recon_cnt);
srv = get_or_create_srv(ctx, &msg->paths_uuid);
- if (!srv) {
+ /*
+ * "refcount == 0" happens if a previous thread calls get_or_create_srv
+ * allocate srv, but chunks of srv are not allocated yet.
+ */
+ if (!srv || refcount_read(&srv->refcount) == 0) {
err = -ENOMEM;
goto reject_w_err;
}
--
2.27.0