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net/smc: Resolve the race between SMC-R link access and clear

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We encountered some crashes caused by the race between SMC-R
link access and link clear that triggered by abnormal link
group termination, such as port error.

Here is an example of this kind of crashes:

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 Workqueue: smc_hs_wq smc_listen_work [smc]
 RIP: 0010:smc_llc_flow_initiate+0x44/0x190 [smc]
 Call Trace:
  <TASK>
  ? __smc_buf_create+0x75a/0x950 [smc]
  smcr_lgr_reg_rmbs+0x2a/0xbf [smc]
  smc_listen_work+0xf72/0x1230 [smc]
  ? process_one_work+0x25c/0x600
  process_one_work+0x25c/0x600
  worker_thread+0x4f/0x3a0
  ? process_one_work+0x600/0x600
  kthread+0x15d/0x1a0
  ? set_kthread_struct+0x40/0x40
  ret_from_fork+0x1f/0x30
  </TASK>

smc_listen_work()                     __smc_lgr_terminate()
---------------------------------------------------------------
                                    | smc_lgr_free()
                                    |  |- smcr_link_clear()
                                    |      |- memset(lnk, 0)
smc_listen_rdma_reg()               |
 |- smcr_lgr_reg_rmbs()             |
     |- smc_llc_flow_initiate()     |
         |- access lnk->lgr (panic) |

These crashes are similarly caused by clearing SMC-R link
resources when some functions is still accessing to them.
This patch tries to fix the issue by introducing reference
count of SMC-R links and ensuring that the sensitive resources
of links won't be cleared until reference count reaches zero.

The operation to the SMC-R link reference count can be concluded
as follows:

object          [hold or initialized as 1]         [put]
--------------------------------------------------------------------
links           smcr_link_init()                   smcr_link_clear()
connections     smc_conn_create()                  smc_conn_free()

Through this way, the clear of SMC-R links is later than the
free of all the smc connections above it, thus avoiding the
unsafe reference to SMC-R links.

Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Wen Gu 2022-01-13 16:36:42 +08:00 committed by David S. Miller
parent ea89c6c098
commit 20c9398d33
2 changed files with 44 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

52
net/smc/smc_core.c
View file

@ -748,6 +748,8 @@ int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
}
get_device(&lnk->smcibdev->ibdev->dev);
atomic_inc(&lnk->smcibdev->lnk_cnt);
refcount_set(&lnk->refcnt, 1); /* link refcnt is set to 1 */
lnk->clearing = 0;
lnk->path_mtu = lnk->smcibdev->pattr[lnk->ibport - 1].active_mtu;
lnk->link_id = smcr_next_link_id(lgr);
lnk->lgr = lgr;
@ -998,8 +1000,12 @@ void smc_switch_link_and_count(struct smc_connection *conn,
struct smc_link *to_lnk)
{
atomic_dec(&conn->lnk->conn_cnt);
/* link_hold in smc_conn_create() */
smcr_link_put(conn->lnk);
conn->lnk = to_lnk;
atomic_inc(&conn->lnk->conn_cnt);
/* link_put in smc_conn_free() */
smcr_link_hold(conn->lnk);
}
struct smc_link *smc_switch_conns(struct smc_link_group *lgr,
@ -1162,6 +1168,8 @@ void smc_conn_free(struct smc_connection *conn)
if (!lgr->conns_num)
smc_lgr_schedule_free_work(lgr);
lgr_put:
if (!lgr->is_smcd)
smcr_link_put(conn->lnk); /* link_hold in smc_conn_create() */
smc_lgr_put(lgr); /* lgr_hold in smc_conn_create() */
}
@ -1218,22 +1226,11 @@ static void smcr_rtoken_clear_link(struct smc_link *lnk)
}
}
/* must be called under lgr->llc_conf_mutex lock */
void smcr_link_clear(struct smc_link *lnk, bool log)
static void __smcr_link_clear(struct smc_link *lnk)
{
struct smc_link_group *lgr = lnk->lgr;
struct smc_ib_device *smcibdev;
if (!lgr || lnk->state == SMC_LNK_UNUSED)
return;
lnk->peer_qpn = 0;
smc_llc_link_clear(lnk, log);
smcr_buf_unmap_lgr(lnk);
smcr_rtoken_clear_link(lnk);
smc_ib_modify_qp_error(lnk);
smc_wr_free_link(lnk);
smc_ib_destroy_queue_pair(lnk);
smc_ib_dealloc_protection_domain(lnk);
smc_wr_free_link_mem(lnk);
smc_ibdev_cnt_dec(lnk);
put_device(&lnk->smcibdev->ibdev->dev);
@ -1245,6 +1242,35 @@ void smcr_link_clear(struct smc_link *lnk, bool log)
smc_lgr_put(lgr); /* lgr_hold in smcr_link_init() */
}
/* must be called under lgr->llc_conf_mutex lock */
void smcr_link_clear(struct smc_link *lnk, bool log)
{
if (!lnk->lgr || lnk->clearing ||
lnk->state == SMC_LNK_UNUSED)
return;
lnk->clearing = 1;
lnk->peer_qpn = 0;
smc_llc_link_clear(lnk, log);
smcr_buf_unmap_lgr(lnk);
smcr_rtoken_clear_link(lnk);
smc_ib_modify_qp_error(lnk);
smc_wr_free_link(lnk);
smc_ib_destroy_queue_pair(lnk);
smc_ib_dealloc_protection_domain(lnk);
smcr_link_put(lnk); /* theoretically last link_put */
}
void smcr_link_hold(struct smc_link *lnk)
{
refcount_inc(&lnk->refcnt);
}
void smcr_link_put(struct smc_link *lnk)
{
if (refcount_dec_and_test(&lnk->refcnt))
__smcr_link_clear(lnk);
}
static void smcr_buf_free(struct smc_link_group *lgr, bool is_rmb,
struct smc_buf_desc *buf_desc)
{
@ -1893,6 +1919,8 @@ int smc_conn_create(struct smc_sock *smc, struct smc_init_info *ini)
}
}
smc_lgr_hold(conn->lgr); /* lgr_put in smc_conn_free() */
if (!conn->lgr->is_smcd)
smcr_link_hold(conn->lnk); /* link_put in smc_conn_free() */
conn->freed = 0;
conn->local_tx_ctrl.common.type = SMC_CDC_MSG_TYPE;
conn->local_tx_ctrl.len = SMC_WR_TX_SIZE;

4
net/smc/smc_core.h
View file

@ -137,6 +137,8 @@ struct smc_link {
u8 peer_link_uid[SMC_LGR_ID_SIZE]; /* peer uid */
u8 link_idx; /* index in lgr link array */
u8 link_is_asym; /* is link asymmetric? */
u8 clearing : 1; /* link is being cleared */
refcount_t refcnt; /* link reference count */
struct smc_link_group *lgr; /* parent link group */
struct work_struct link_down_wrk; /* wrk to bring link down */
char ibname[IB_DEVICE_NAME_MAX]; /* ib device name */
@ -526,6 +528,8 @@ void smc_core_exit(void);
int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
u8 link_idx, struct smc_init_info *ini);
void smcr_link_clear(struct smc_link *lnk, bool log);
void smcr_link_hold(struct smc_link *lnk);
void smcr_link_put(struct smc_link *lnk);
void smc_switch_link_and_count(struct smc_connection *conn,
struct smc_link *to_lnk);
int smcr_buf_map_lgr(struct smc_link *lnk);