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

[Jens Axboe]

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?

--
Jens Axboe

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