[dm-devel] [PATCH 0/7] dm-mpath: Fix a race condition in the blk-mq path

[Bart Van Assche]

On 11/16/2016 06:56 AM, Mike Snitzer wrote:
> 7 is not acceptable.  It complicates the code for no reason (the
> scenario that it is meant to address isn't possible).

Hello Mike,

With patch (a) applied I see warning (b) appear a few seconds after I 
start test 02-sq from the srp-test suite. I think that shows that 
something like patch (7) is really needed. Please let me know if you 
need more information about my test setup.

Bart.


(a)

@@ -568,8 +568,10 @@ static int __multipath_map(struct dm_target *ti, 
struct requ
est *clone,
          * multiqueue path is added before __multipath_map() is called. If
          * that happens requeue to trigger unprepare and reprepare.
          */
-       if ((clone && q->mq_ops) || (!clone && !q->mq_ops))
+       if ((clone && q->mq_ops) || (!clone && !q->mq_ops)) {
+               WARN_ON_ONCE(true);
                 return r;
+       }

         mpio = set_mpio(m, map_context);
         if (!mpio)

(b)

------------[ cut here ]------------
WARNING: CPU: 9 PID: 542 at drivers/md/dm-mpath.c:584 
__multipath_map.isra.15+0x1e2/0x390 [dm_multipath]
Modules linked in: ib_srp scsi_transport_srp ib_srpt(O) scst_vdisk(O) 
scst(O) dlm libcrc32c brd dm_service_time netconsole xt_CHECKSUM 
iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat 
nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conn track 
nf_conntrack ipt_REJECT xt_tcpudp tun bridge stp llc ebtable_filter 
ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables 
af_packet ib_ipoib rdma_ucm ib_ucm ib_uverbs msr ib_umad rdma_cm 
configfs ib_cm iw_cm mlx4_ib ib_core sb_edac edac_core 
x86_pkg_temp_thermal coretemp kvm_intel kvm ipmi_ssif ipmi_devintf 
mlx4_core irqbypass hid_generic crct10dif_pclmul crc32_pclmul usbhid 
ghash_clmulni_intel aesni_intel aes_x86_64 lrw tg3 gf128mul glue_helper 
iTCO_wdt ptp iTCO_vendor_support pps_core dcdbas ablk_helper pcspkr 
ipmi_si libphy cryptd mei_me ipmi_msghandler fjes tpm_tis mei 
tpm_tis_core tpm lpc_ich shpchp mfd_core wmi button mgag200 i2c_algo_bit 
drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm 
sr_mod cdrom crc32c_intel ehci_pci ehci_hcd usbcore usb_common sg 
dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua [last 
unloaded: brd]
CPU: 9 PID: 542 Comm: kworker/9:1H Tainted: G           O 
4.9.0-rc5-dbg+ #1
Hardware name: Dell Inc. PowerEdge R430/03XKDV, BIOS 1.0.2 11/17/2014
Workqueue: kblockd blk_mq_requeue_work
  ffffc9000251fb08 ffffffff81329555 0000000000000000 0000000000000000
  ffffc9000251fb48 ffffffff81064a56 0000024800000000 ffff8803f2a3ba78
  ffff8803f2a32758 0000000000000000 ffff8804519de528 0000000000000000
Call Trace:
  [<ffffffff81329555>] dump_stack+0x68/0x93
  [<ffffffff81064a56>] __warn+0xc6/0xe0
  [<ffffffff81064b28>] warn_slowpath_null+0x18/0x20
  [<ffffffffa0046372>] __multipath_map.isra.15+0x1e2/0x390 [dm_multipath]
  [<ffffffffa0046535>] multipath_clone_and_map+0x15/0x20 [dm_multipath]
  [<ffffffffa002a3ed>] map_request+0x14d/0x3a0 [dm_mod]
  [<ffffffffa002a6e7>] dm_mq_queue_rq+0x77/0x110 [dm_mod]
  [<ffffffff8131083f>] blk_mq_process_rq_list+0x23f/0x340
  [<ffffffff81310a62>] __blk_mq_run_hw_queue+0x122/0x1c0
  [<ffffffff81310a1e>] ? __blk_mq_run_hw_queue+0xde/0x1c0
  [<ffffffff813105df>] blk_mq_run_hw_queue+0x9f/0xc0
  [<ffffffff81310bae>] blk_mq_run_hw_queues+0x6e/0x90
  [<ffffffff81312b37>] blk_mq_requeue_work+0xf7/0x110
  [<ffffffff81082ab5>] process_one_work+0x1f5/0x690
  [<ffffffff81082a3a>] ? process_one_work+0x17a/0x690
  [<ffffffff81082f99>] worker_thread+0x49/0x490
  [<ffffffff81082f50>] ? process_one_work+0x690/0x690
  [<ffffffff81082f50>] ? process_one_work+0x690/0x690
  [<ffffffff8108983b>] kthread+0xeb/0x110
  [<ffffffff81089750>] ? kthread_park+0x60/0x60
  [<ffffffff8163ef87>] ret_from_fork+0x27/0x40
---[ end trace 81cfd74742407be1 ]---

Bart.