Commit 20c9398d authored by Wen Gu's avatar Wen Gu Committed by David S. Miller
Browse files

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



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: default avatarWen Gu <guwen@linux.alibaba.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ea89c6c0

net/smc/smc_core.c

+40 −12
Original line number Diff line number Diff line
@@ -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;

net/smc/smc_core.h

+4 −0
Original line number Diff line number Diff line
@@ -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);