From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Battersby Subject: Re: [PATCH] libata: revert "libata: use blk taging" et al. Date: Wed, 11 Mar 2015 18:19:27 -0400 Message-ID: <5500BF6F.6080000@cybernetics.com> References: <5500863D.4070807@cybernetics.com> <5500B783.20106@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5500B783.20106@fb.com> Sender: linux-kernel-owner@vger.kernel.org To: Jens Axboe , Tejun Heo , Shaohua Li , linux-ide@vger.kernel.org Cc: Christoph Hellwig , Dan Williams , linux-kernel@vger.kernel.org List-Id: linux-ide@vger.kernel.org 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: [] 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:[] [] 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: >> [] ata_scsi_translate+0x3d/0x1b0 >> [] ata_sas_queuecmd+0x149/0x2a0 >> [] sas_queuecommand+0xa0/0x1f0 [libsas] >> [] scsi_dispatch_cmd+0xd4/0x1a0 >> [] scsi_queue_rq+0x66f/0x7f0 >> [] __blk_mq_run_hw_queue+0x208/0x3f0 >> [] blk_mq_run_hw_queue+0x88/0xc0 >> [] blk_mq_insert_request+0xc4/0x130 >> [] blk_execute_rq_nowait+0x73/0x160 >> [] sg_common_write+0x3da/0x720 [sg] >> [] ? might_fault+0x5e/0xb0 >> [] sg_new_write+0x250/0x360 [sg] >> [] ? __lock_acquire+0x50c/0xc10 >> [] ? lock_release_non_nested+0xa7/0x360 >> [] ? _raw_spin_unlock_irqrestore+0x3b/0x60 >> [] ? might_fault+0x5e/0xb0 >> [] ? might_fault+0x5e/0xb0 >> [] sg_write+0x13b/0x450 [sg] >> [] ? __lock_acquire+0x50c/0xc10 >> [] ? do_futex+0x109/0xbf0 >> [] ? might_fault+0x5e/0xb0 >> [] vfs_write+0xd1/0x1b0 >> [] SyS_write+0x54/0xc0 >> [] 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 [] ata_qc_new_init+0x3e/0x120 >> RSP >> 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. Tony