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From:   liuyacan@corp.netease.com
To:     wintera@linux.ibm.com
Cc:     davem@davemloft.net, edumazet@google.com, kgraul@linux.ibm.com,
        kuba@kernel.org, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org, liuyacan@corp.netease.com,
        netdev@vger.kernel.org, pabeni@redhat.com,
        tonylu@linux.alibaba.com, wenjia@linux.ibm.com
Subject: Re: [PATCH net v2] net/smc: fix listen processing for SMC-Rv2
Date:   Thu,  1 Sep 2022 00:08:42 +0800
Message-Id: <20220831160842.1827396-1-liuyacan@corp.netease.com>
In-Reply-To: <b3245c33-125c-7483-318a-a78dfbdac5ee@linux.ibm.com>
References: <b3245c33-125c-7483-318a-a78dfbdac5ee@linux.ibm.com>
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> >>> From: liuyacan <liuyacan@corp.netease.com>
> >>>
> >>> After modifying the QP to the Error state, all RX WR would be
> >>> completed with WC in IB_WC_WR_FLUSH_ERR status. Current
> >>> implementation does not wait for it is done, but free the link
> >>> directly. So there is a risk that accessing the freed link in
> >>> tasklet context.
> >>>
> >>> Here is a crash example:
> >>>
> >>>  BUG: unable to handle page fault for address: ffffffff8f220860
> >>>  #PF: supervisor write access in kernel mode
> >>>  #PF: error_code(0x0002) - not-present page
> >>>  PGD f7300e067 P4D f7300e067 PUD f7300f063 PMD 8c4e45063 PTE 800ffff08c9df060
> >>>  Oops: 0002 [#1] SMP PTI
> >>>  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: G S         OE     5.10.0-0607+ #23
> >>>  Hardware name: Inspur NF5280M4/YZMB-00689-101, BIOS 4.1.20 07/09/2018
> >>>  RIP: 0010:native_queued_spin_lock_slowpath+0x176/0x1b0
> >>>  Code: f3 90 48 8b 32 48 85 f6 74 f6 eb d5 c1 ee 12 83 e0 03 83 ee 01 48 c1 e0 05 48 63 f6 48 05 00 c8 02 00 48 03 04 f5 00 09 98 8e <48> 89 10 8b 42 08 85 c0 75 09 f3 90 8b 42 08 85 c0 74 f7 48 8b 32
> >>>  RSP: 0018:ffffb3b6c001ebd8 EFLAGS: 00010086
> >>>  RAX: ffffffff8f220860 RBX: 0000000000000246 RCX: 0000000000080000
> >>>  RDX: ffff91db1f86c800 RSI: 000000000000173c RDI: ffff91db62bace00
> >>>  RBP: ffff91db62bacc00 R08: 0000000000000000 R09: c00000010000028b
> >>>  R10: 0000000000055198 R11: ffffb3b6c001ea58 R12: ffff91db80e05010
> >>>  R13: 000000000000000a R14: 0000000000000006 R15: 0000000000000040
> >>>  FS:  0000000000000000(0000) GS:ffff91db1f840000(0000) knlGS:0000000000000000
> >>>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >>>  CR2: ffffffff8f220860 CR3: 00000001f9580004 CR4: 00000000003706e0
> >>>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >>>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >>>  Call Trace:
> >>>   <IRQ>
> >>>   _raw_spin_lock_irqsave+0x30/0x40
> >>>   mlx5_ib_poll_cq+0x4c/0xc50 [mlx5_ib]
> >>>   smc_wr_rx_tasklet_fn+0x56/0xa0 [smc]
> >>>   tasklet_action_common.isra.21+0x66/0x100
> >>>   __do_softirq+0xd5/0x29c
> >>>   asm_call_irq_on_stack+0x12/0x20
> >>>   </IRQ>
> >>>   do_softirq_own_stack+0x37/0x40
> >>>   irq_exit_rcu+0x9d/0xa0
> >>>   sysvec_call_function_single+0x34/0x80
> >>>   asm_sysvec_call_function_single+0x12/0x20
> >>>
> >>> Signed-off-by: liuyacan <liuyacan@corp.netease.com>
> >>> ---
> >>>  net/smc/smc_core.c |  2 ++
> >>>  net/smc/smc_core.h |  2 ++
> >>>  net/smc/smc_wr.c   | 12 ++++++++++++
> >>>  net/smc/smc_wr.h   |  3 +++
> >>>  4 files changed, 19 insertions(+)
> >>>
> >>> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
> >>> index ff49a11f5..b632a33f1 100644
> >>> --- a/net/smc/smc_core.c
> >>> +++ b/net/smc/smc_core.c
> >>> @@ -752,6 +752,7 @@ int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
> >>>  	atomic_inc(&lnk->smcibdev->lnk_cnt);
> >>>  	refcount_set(&lnk->refcnt, 1); /* link refcnt is set to 1 */
> >>>  	lnk->clearing = 0;
> >>> +	lnk->rx_drained = 0;
> >>>  	lnk->path_mtu = lnk->smcibdev->pattr[lnk->ibport - 1].active_mtu;
> >>>  	lnk->link_id = smcr_next_link_id(lgr);
> >>>  	lnk->lgr = lgr;
> >>> @@ -1269,6 +1270,7 @@ void smcr_link_clear(struct smc_link *lnk, bool log)
> >>>  	smcr_buf_unmap_lgr(lnk);
> >>>  	smcr_rtoken_clear_link(lnk);
> >>>  	smc_ib_modify_qp_error(lnk);
> >>> +	smc_wr_drain_cq(lnk);
> >>>  	smc_wr_free_link(lnk);
> >>>  	smc_ib_destroy_queue_pair(lnk);
> >>>  	smc_ib_dealloc_protection_domain(lnk);
> >>> diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
> >>> index fe8b524ad..0a469a3e7 100644
> >>> --- a/net/smc/smc_core.h
> >>> +++ b/net/smc/smc_core.h
> >>> @@ -117,6 +117,7 @@ struct smc_link {
> >>>  	u64			wr_rx_id;	/* seq # of last recv WR */
> >>>  	u32			wr_rx_cnt;	/* number of WR recv buffers */
> >>>  	unsigned long		wr_rx_tstamp;	/* jiffies when last buf rx */
> >>> +	wait_queue_head_t       wr_rx_drain_wait; /* wait for WR drain */
> >>>  
> >>>  	struct ib_reg_wr	wr_reg;		/* WR register memory region */
> >>>  	wait_queue_head_t	wr_reg_wait;	/* wait for wr_reg result */
> >>> @@ -138,6 +139,7 @@ struct smc_link {
> >>>  	u8			link_idx;	/* index in lgr link array */
> >>>  	u8			link_is_asym;	/* is link asymmetric? */
> >>>  	u8			clearing : 1;	/* link is being cleared */
> >>> +	u8                      rx_drained : 1; /* link is drained */
> >>>  	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 */
> >>> diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
> >>> index 26f8f240d..f9992896a 100644
> >>> --- a/net/smc/smc_wr.c
> >>> +++ b/net/smc/smc_wr.c
> >>> @@ -465,6 +465,10 @@ static inline void smc_wr_rx_process_cqes(struct ib_wc wc[], int num)
> >>>  			case IB_WC_RNR_RETRY_EXC_ERR:
> >>>  			case IB_WC_WR_FLUSH_ERR:
> >>>  				smcr_link_down_cond_sched(link);
> >>> +				if (link->clearing && wc[i]->wr_id == link->wr_rx_id) {
> >>> +					link->rx_drained = 1;
> >>> +					wake_up(&link->wr_rx_drain_wait);
> >>> +				}
> >>
> >> I am wondering if we should wait for all the wc comes back?
> > 
> > I think yes, so other processes can safely destroy qp.
> > 
> >>
> >>>  				break;
> >>>  			default:
> >>>  				smc_wr_rx_post(link); /* refill WR RX */
> >>> @@ -631,6 +635,13 @@ static void smc_wr_init_sge(struct smc_link *lnk)
> >>>  	lnk->wr_reg.access = IB_ACCESS_LOCAL_WRITE | IB_ACCESS_REMOTE_WRITE;
> >>>  }
> >>>  
> >>> +void smc_wr_drain_cq(struct smc_link *lnk)
> >>> +{
> >>> +	wait_event_interruptible_timeout(lnk->wr_rx_drain_wait,
> >>> +					 (lnk->drained == 1),
> >>> +					 SMC_WR_RX_WAIT_DRAIN_TIME);
> >>> +}
> >>
> >> Should we wait for it with timeout? It should eventually be wake up
> >> normally before freeing link. Waiting for SMC_WR_RX_WAIT_DRAIN_TIME (2s)
> >> may also have this issue, although the probability of occurrence is
> >> greatly reduced.
> > 
> > Indeed, there should logically probably be a perpetual wait here. I'm just worried if it 
> > will get stuck for some unknown reason.
> > 
> >>
> >> Cheers,
> >> Tony Lu
> > 
> > Regards,
> > Yacan
> > 
> 
> Thank you very much for working on a fix, Yacan.
> 
> Some comments to make reviewers' lives easier:
> Please use your real name for the Signed-Off tag and Mail sender (Is it Yacan Liu ?)
> (Please use the same Mail address for all your posts. In April there was a post from yacanliu@163.com. Not this one)
>
> Important: Add a Fixes tag, when sending fixes to NET

OK. I updated in the latest version (v4) 

> Is this mail really a reply to your v2? Or rather a reply to Tony's comments on v1?

It should be v1. But now v1~v3 are abandoned.

> 
> Kind regards
> Alexandra

Regards,
Yacan