Re: [PATCH] libata: revert "libata: use blk taging" et al.

[Shaohua Li]

On Wed, Mar 11, 2015 at 06:19:27PM -0400, Tony Battersby wrote:
> On 03/11/2015 05:45 PM, Jens Axboe wrote:
> > On 03/11/2015 02:15 PM, Tony Battersby wrote:
> >> This reverts commits 12cb5ce101abfaf74421f8cc9f196e708209eb79 and
> >> 98bd4be1ba95f2fe7f543910792b7163a5de06eb.
> >>
> >> Commit 12cb5ce101ab ("libata: use blk taging") causes the following oops
> >> with scsi-mq enabled:
> >>
> >> BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
> >> IP: [<ffffffff804fd46e>] ata_qc_new_init+0x3e/0x120
> >> PGD 32adf0067 PUD 32adf1067 PMD 0
> >> Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
> >> Modules linked in: iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi igb
> >> i2c_algo_bit ptp pps_core pm80xx libsas scsi_transport_sas sg coretemp
> >> eeprom w83795 i2c_i801
> >> CPU: 4 PID: 1450 Comm: cydiskbench Not tainted 4.0.0-rc3 #1
> >> Hardware name: Supermicro X8DTH-i/6/iF/6F/X8DTH, BIOS 2.1b       05/04/12
> >> task: ffff8800ba86d500 ti: ffff88032a064000 task.ti: ffff88032a064000
> >> RIP: 0010:[<ffffffff804fd46e>]  [<ffffffff804fd46e>] ata_qc_new_init+0x3e/0x120
> >> RSP: 0018:ffff88032a067858  EFLAGS: 00010046
> >> RAX: 0000000000000000 RBX: ffff8800ba0d2230 RCX: 000000000000002a
> >> RDX: ffffffff80505ae0 RSI: 0000000000000020 RDI: ffff8800ba0d2230
> >> RBP: ffff88032a067868 R08: 0000000000000201 R09: 0000000000000001
> >> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800ba0d0000
> >> R13: ffff8800ba0d2230 R14: ffffffff80505ae0 R15: ffff8800ba0d0000
> >> FS:  0000000041223950(0063) GS:ffff88033e480000(0000) knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> >> CR2: 0000000000000058 CR3: 000000032a0a3000 CR4: 00000000000006e0
> >> Stack:
> >>   ffff880329eee758 ffff880329eee758 ffff88032a0678a8 ffffffff80502dad
> >>   ffff8800ba167978 ffff880329eee758 ffff88032bf9c520 ffff8800ba167978
> >>   ffff88032bf9c520 ffff88032bf9a290 ffff88032a0678b8 ffffffff80506909
> >> Call Trace:
> >>   [<ffffffff80502dad>] ata_scsi_translate+0x3d/0x1b0
> >>   [<ffffffff80506909>] ata_sas_queuecmd+0x149/0x2a0
> >>   [<ffffffffa0046650>] sas_queuecommand+0xa0/0x1f0 [libsas]
> >>   [<ffffffff804ea544>] scsi_dispatch_cmd+0xd4/0x1a0
> >>   [<ffffffff804eb50f>] scsi_queue_rq+0x66f/0x7f0
> >>   [<ffffffff803e5098>] __blk_mq_run_hw_queue+0x208/0x3f0
> >>   [<ffffffff803e54b8>] blk_mq_run_hw_queue+0x88/0xc0
> >>   [<ffffffff803e5c74>] blk_mq_insert_request+0xc4/0x130
> >>   [<ffffffff803e0b63>] blk_execute_rq_nowait+0x73/0x160
> >>   [<ffffffffa0023fca>] sg_common_write+0x3da/0x720 [sg]
> >>   [<ffffffff80308b8e>] ? might_fault+0x5e/0xb0
> >>   [<ffffffffa0025100>] sg_new_write+0x250/0x360 [sg]
> >>   [<ffffffff802a236c>] ? __lock_acquire+0x50c/0xc10
> >>   [<ffffffff802a2b87>] ? lock_release_non_nested+0xa7/0x360
> >>   [<ffffffff8068954b>] ? _raw_spin_unlock_irqrestore+0x3b/0x60
> >>   [<ffffffff80308b8e>] ? might_fault+0x5e/0xb0
> >>   [<ffffffff80308b8e>] ? might_fault+0x5e/0xb0
> >>   [<ffffffffa0025feb>] sg_write+0x13b/0x450 [sg]
> >>   [<ffffffff802a236c>] ? __lock_acquire+0x50c/0xc10
> >>   [<ffffffff802cb1e9>] ? do_futex+0x109/0xbf0
> >>   [<ffffffff80308b8e>] ? might_fault+0x5e/0xb0
> >>   [<ffffffff8032ec91>] vfs_write+0xd1/0x1b0
> >>   [<ffffffff8032ee54>] SyS_write+0x54/0xc0
> >>   [<ffffffff80689932>] system_call_fastpath+0x12/0x17
> >> Code: 24 20 04 0f 85 ec 00 00 00 49 83 3c 24 00 0f 84 cf 00 00 00 83 fe 1f
> >> 0f 87 dc 00 00 00 89 f0 48 69 c0 f0 00 00 00 49 8d 44 04 40 <89> 70 58 48
> >> c7 40 10 00 00 00 00 4c 89 20 48 89 58 08 c7 40 64
> >> RIP  [<ffffffff804fd46e>] ata_qc_new_init+0x3e/0x120
> >>   RSP <ffff88032a067858>
> >> CR2: 0000000000000058
> >> ---[ end trace 43f5eefb64627eff ]---
> >>
> >>
> >> scsi-mq uses a host-wide tag map shared among all devices with some
> >> integer tag values >= ATA_MAX_QUEUE.  These unexpectedly high tag values
> >> cause __ata_qc_from_tag() to return NULL, which is then dereferenced in
> >> ata_qc_new_init(), causing the oops above.
> > Wait, something is missing here. We should not be getting tag values 
> > that are >= ATA_MAX_QUEUE. Instead of reverting this, we need to figure 
> > out why this is happening, and fix it. That is correct way forward here. 
> > What setup is this being reproduced on?
> >
> 
> Hardware:
> PMC 8001 SAS HBA (PCI ID 117c:0042, PCI sub-ID 117c:0043) using pm80xx
> driver
> 4 SATA disks directly connected (no expander)
> 
> Test procedure:
> Send disk read/write commands to SATA disks using the SCSI generic (sg)
> driver.
> 
> Analysis:
> 
> shost->can_queue is 508
> 
> With my patch applied to revert the problematic commits, I added the
> following code to ata_scsi_qc_new():
> 
>     int tag = cmd->request->tag;
>     static int max_tag;
>     if (tag > max_tag) {
>         max_tag = tag;
>         printk(KERN_DEBUG "max tag %d\n", tag);
>     }
> 
> Testing one SATA disk at a time with scsi-mq enabled, I get a max tag of
> 64.  Testing 4 disks at a time with scsi-mq enabled gives a max tag of
> 194.  With scsi-mq disabled, I get a max tag of 30 no matter how many
> disks I test.

ata_qc_new_init() has a check, if !ap->scsi_host, request tag will not
be used and fallback to original tag allocation. you are using sas
controller, so the problem is why ap->scsi_host is set in your case.

Thanks,
Shaohua
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