Re: [PATCH] scsi: sd_zbc: update write pointer offset cache

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Mar 12, 2021 / 08:58, Johannes Thumshirn wrote:
> On 12/03/2021 09:20, Damien Le Moal wrote:
> > On 2021/03/12 16:59, Johannes Thumshirn wrote:
> >> On 12/03/2021 08:27, Damien Le Moal wrote:
> >>> On 2021/03/12 13:38, Shinichiro Kawasaki wrote:
> >>>> On Mar 11, 2021 / 15:54, Johannes Thumshirn wrote:
> >>>>> On 11/03/2021 16:48, Bart Van Assche wrote:
> >>>>>> On 3/11/21 7:18 AM, Johannes Thumshirn wrote:
> >>>>>>> On 11/03/2021 16:13, Bart Van Assche wrote:
> >>>>>>>> On 3/10/21 1:48 AM, Johannes Thumshirn wrote:
> >>>>>>>>> Recent changes [ ... ]
> >>>>>>>>
> >>>>>>>> Please add Fixes: and/or Cc: stable tags as appropriate.
> >>>>>>>
> >>>>>>> I couldn't pin down the offending commit and I can't reproduce it locally
> >>>>>>> as well, so I opted out of this. But it must be something between v5.11 and v5.12-rc2.
> >>>>>>
> >>>>>> That's weird. Did Shinichiro use a HBA? Could this be the result of a
> >>>>>> behavior change in the HBA driver?
> >>>>>
> >>>>> Yes I've looked at the commits in mpt3sas, but can't really pinpoint the 
> >>>>> offending commit TBH. 664f0dce2058 ("scsi: mpt3sas: Add support for shared 
> >>>>> host tagset for CPU hotplug") is the only one that /looks/ as if it could
> >>>>> be causing it, but I don't know mpt3sas well enough.
> >>>>>
> >>>>> FWIW added Sreekanth
> >>>>
> >>>> The WARNING was found in kernel v5.12-rc2 test with a SAS SMR drive and HBA
> >>>> Broadcom 9400. It can be recreated by running blktests block/004 on the drive
> >>>> (after reboot). It is also recreated with SATA SMR drive with the HBA, but not
> >>>> observed with SATA drives connected to AHCI.
> >>>>
> >>>> I reverted the commit 664f0dce2058, then the WARNING disappeared. I suppose
> >>>> it indicates that the commit changed HBA driver behavior.
> >>>
> >>> Can you send the warning splat with backtrace ?
> >>>
> >>
> >> The warning splat is in the commit message:
> >> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc2+ #2
> >>  Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0 12/17/2015
> >>  RIP: 0010:__local_bh_disable_ip+0x3f/0x50
> >>  RSP: 0018:ffff8883e1409ba8 EFLAGS: 00010006
> >>  RAX: 0000000080010001 RBX: 0000000000000001 RCX: 0000000000000013
> >>  RDX: ffff888129e4d200 RSI: 0000000000000201 RDI: ffffffff915b9dbd
> >>  RBP: ffff888113e9a540 R08: ffff888113e9a540 R09: 00000000000077f0
> >>  R10: 0000000000080000 R11: 0000000000000001 R12: ffff888129e4d200
> >>  R13: 0000000000001000 R14: 00000000000077f0 R15: ffff888129e4d218
> >>  FS:  0000000000000000(0000) GS:ffff8883e1400000(0000) knlGS:0000000000000000
> >>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >>  CR2: 00007f2f8418ebc0 CR3: 000000021202a006 CR4: 00000000001706f0
> >>  Call Trace:
> >>   <IRQ>
> >>   _raw_spin_lock_bh+0x18/0x40
> >>   sd_zbc_complete+0x43d/0x1150
> >>   sd_done+0x631/0x1040
> >>   ? mark_lock+0xe4/0x2fd0
> >>   ? provisioning_mode_store+0x3f0/0x3f0
> >>   scsi_finish_command+0x31b/0x5c0
> >>   _scsih_io_done+0x960/0x29e0 [mpt3sas]
> >>   ? mpt3sas_scsih_scsi_lookup_get+0x1c7/0x340 [mpt3sas]
> >>   ? __lock_acquire+0x166b/0x58b0
> >>   ? _get_st_from_smid+0x4a/0x80 [mpt3sas]
> >>   _base_process_reply_queue+0x23f/0x26e0 [mpt3sas]
> >>   ? lock_is_held_type+0x98/0x110
> >>   ? find_held_lock+0x2c/0x110
> >>   ? mpt3sas_base_sync_reply_irqs+0x360/0x360 [mpt3sas]
> >>   _base_interrupt+0x8d/0xd0 [mpt3sas]
> >>   ? rcu_read_lock_sched_held+0x3f/0x70
> >>   __handle_irq_event_percpu+0x24d/0x600
> >>   handle_irq_event+0xef/0x240
> >>   ? handle_irq_event_percpu+0x110/0x110
> >>   handle_edge_irq+0x1f6/0xb60
> >>   __common_interrupt+0x75/0x160
> >>   common_interrupt+0x7b/0xa0
> >>   </IRQ>
> >>   asm_common_interrupt+0x1e/0x40
> >>
> > 
> > Looking at patch 664f0dce2058, all that seems to be done is to enable
> > nr_hw_queue > 1. I do not see any change of locking context or irq handling.
> > From the backtrace, it does not look like scsi_finish_command() is called from
> > softirq... Probably a change in that area is responsible ?
> > 
> 
> 
> In scsi_lib.c we only have these two patches in that area:
> 
> 684da7628d93 ("block: remove unnecessary argument from blk_execute_rq")
> 962c8dcdd5fa ("scsi: core: Add a new error code DID_TRANSPORT_MARGINAL in scsi.h")
> 
> and none of them can cause the failure either. In block we have:
> 
> 0a2efafbb1c7 ("blk-mq: Always complete remote completions requests in softirq")
> 
> but this doesn't look guilty as well, all it does is raising a softirq for all
> block completions local and remote.

In blk_mq_complete_request_remote(), I found the following code.

	if (rq->q->nr_hw_queues == 1) {
		blk_mq_raise_softirq(rq);
		return true;
	}
	return false;

My mere guess is that the commit 664f0dce2058 changed the shost->nr_hw_queue
from zero to a value larger than 1 (with my test system, it is 8), it is
propagated to rq->q->nr_hw_queues, then blk_mq_raise_softirq() is no longer
called.

The call stack I assume is as follows: without calling blk_mq_raise_softirq(),
there are all executed in IRQ context, probably.

  _scsih_io_done()
    scmd->scsi_done() = scsi_mq_done()
      blk_mq_complete_request()
        blk_mq_complete_request_remote() ... did not call blk_mq_raise_softirq()
        rq->q->mq_ops->complete() = scsi_soft_irq_done()
	  scsi_finish_command()
	    drv->done() = sd_done()

Will confirm this guess further.

-- 
Best Regards,
Shin'ichiro Kawasaki