Re: [PATCH] blk-mq: only run mapped hw queues in blk_mq_run_hw_queues()

[Ming Lei <ming.lei@redhat.com>]

On Thu, Mar 29, 2018 at 11:09:08AM +0200, Christian Borntraeger wrote:
> 
> 
> On 03/29/2018 09:23 AM, Christian Borntraeger wrote:
> > 
> > 
> > On 03/29/2018 04:00 AM, Ming Lei wrote:
> >> On Wed, Mar 28, 2018 at 05:36:53PM +0200, Christian Borntraeger wrote:
> >>>
> >>>
> >>> On 03/28/2018 05:26 PM, Ming Lei wrote:
> >>>> Hi Christian,
> >>>>
> >>>> On Wed, Mar 28, 2018 at 09:45:10AM +0200, Christian Borntraeger wrote:
> >>>>> FWIW, this patch does not fix the issue for me:
> >>>>>
> >>>>> ostname=? addr=? terminal=? res=success'
> >>>>> [   21.454961] WARNING: CPU: 3 PID: 1882 at block/blk-mq.c:1410 __blk_mq_delay_run_hw_queue+0xbe/0xd8
> >>>>> [   21.454968] Modules linked in: scsi_dh_rdac scsi_dh_emc scsi_dh_alua dm_mirror dm_region_hash dm_log dm_multipath dm_mod autofs4
> >>>>> [   21.454984] CPU: 3 PID: 1882 Comm: dasdconf.sh Not tainted 4.16.0-rc7+ #26
> >>>>> [   21.454987] Hardware name: IBM 2964 NC9 704 (LPAR)
> >>>>> [   21.454990] Krnl PSW : 00000000c0131ea3 000000003ea2f7bf (__blk_mq_delay_run_hw_queue+0xbe/0xd8)
> >>>>> [   21.454996]            R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
> >>>>> [   21.455005] Krnl GPRS: 0000013abb69a000 0000013a00000000 0000013ac6c0dc00 0000000000000001
> >>>>> [   21.455008]            0000000000000000 0000013abb69a710 0000013a00000000 00000001b691fd98
> >>>>> [   21.455011]            00000001b691fd98 0000013ace4775c8 0000000000000001 0000000000000000
> >>>>> [   21.455014]            0000013ac6c0dc00 0000000000b47238 00000001b691fc08 00000001b691fbd0
> >>>>> [   21.455032] Krnl Code: 000000000069c596: ebaff0a00004	lmg	%r10,%r15,160(%r15)
> >>>>>                           000000000069c59c: c0f4ffff7a5e	brcl	15,68ba58
> >>>>>                          #000000000069c5a2: a7f40001		brc	15,69c5a4
> >>>>>                          >000000000069c5a6: e340f0c00004	lg	%r4,192(%r15)
> >>>>>                           000000000069c5ac: ebaff0a00004	lmg	%r10,%r15,160(%r15)
> >>>>>                           000000000069c5b2: 07f4		bcr	15,%r4
> >>>>>                           000000000069c5b4: c0e5fffffeea	brasl	%r14,69c388
> >>>>>                           000000000069c5ba: a7f4fff6		brc	15,69c5a6
> >>>>> [   21.455067] Call Trace:
> >>>>> [   21.455072] ([<00000001b691fd98>] 0x1b691fd98)
> >>>>> [   21.455079]  [<000000000069c692>] blk_mq_run_hw_queue+0xba/0x100 
> >>>>> [   21.455083]  [<000000000069c740>] blk_mq_run_hw_queues+0x68/0x88 
> >>>>> [   21.455089]  [<000000000069b956>] __blk_mq_complete_request+0x11e/0x1d8 
> >>>>> [   21.455091]  [<000000000069ba9c>] blk_mq_complete_request+0x8c/0xc8 
> >>>>> [   21.455103]  [<00000000008aa250>] dasd_block_tasklet+0x158/0x490 
> >>>>> [   21.455110]  [<000000000014c742>] tasklet_hi_action+0x92/0x120 
> >>>>> [   21.455118]  [<0000000000a7cfc0>] __do_softirq+0x120/0x348 
> >>>>> [   21.455122]  [<000000000014c212>] irq_exit+0xba/0xd0 
> >>>>> [   21.455130]  [<000000000010bf92>] do_IRQ+0x8a/0xb8 
> >>>>> [   21.455133]  [<0000000000a7c298>] io_int_handler+0x130/0x298 
> >>>>> [   21.455136] Last Breaking-Event-Address:
> >>>>> [   21.455138]  [<000000000069c5a2>] __blk_mq_delay_run_hw_queue+0xba/0xd8
> >>>>> [   21.455140] ---[ end trace be43f99a5d1e553e ]---
> >>>>> [   21.510046] dasdconf.sh Warning: 0.0.241e is already online, not configuring
> >>>>
> >>>> Thinking about this issue further, I can't understand the root cause for
> >>>> this issue.
> 
> FWIW, Limiting CONFIG_NR_CPUS to 64 seems to make the problem go away.

I think the following patch is needed, and this way aligns to the mapping
created via managed IRQ at least.

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 9f8cffc8a701..638ab5c11b3c 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -14,13 +14,12 @@
 #include "blk.h"
 #include "blk-mq.h"
 
+/*
+ * Given there isn't CPU hotplug handler in blk-mq, map all possible CPUs to
+ * queues even it isn't present yet.
+ */
 static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
 {
-	/*
-	 * Non present CPU will be mapped to queue index 0.
-	 */
-	if (!cpu_present(cpu))
-		return 0;
 	return cpu % nr_queues;
 }

Thanks,
Ming