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Message-Id: <20220831160842.1827396-1-liuyacan@corp.netease.com>
Date: Thu, 1 Sep 2022 00:08:42 +0800
From: liuyacan@...p.netease.com
To: wintera@...ux.ibm.com
Cc: davem@...emloft.net, edumazet@...gle.com, kgraul@...ux.ibm.com,
kuba@...nel.org, linux-kernel@...r.kernel.org,
linux-s390@...r.kernel.org, liuyacan@...p.netease.com,
netdev@...r.kernel.org, pabeni@...hat.com,
tonylu@...ux.alibaba.com, wenjia@...ux.ibm.com
Subject: Re: [PATCH net v2] net/smc: fix listen processing for SMC-Rv2
> >>> From: liuyacan <liuyacan@...p.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@...p.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@....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
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