Re: SCSI bug

[Helge Deller <deller@gmx.de>]

On 23.02.2016 04:04, John David Anglin wrote:
> On 2016-02-21, at 10:24 PM, John David Anglin wrote:
> 
>> On 2016-02-21, at 7:53 PM, John David Anglin wrote:
>>
>>> Backtrace:                                                                      
>>> [<000000004046f4b0>] scsi_init_sgtable+0x70/0xb8                               
>>> [<000000004046f564>] scsi_init_io+0x6c/0x220                                   
>>> [<000000000811c5c0>] sd_setup_read_write_cmnd+0x58/0x968 [sd_mod]              
>>> [<000000000811cf14>] sd_init_command+0x44/0x130 [sd_mod]                       
>>> [<000000004046f81c>] scsi_setup_cmnd+0x104/0x1b0                               
>>> [<000000004046fab8>] scsi_prep_fn+0x100/0x1a0                                  
>>> [<000000004035b9b0>] blk_peek_request+0x1b8/0x298                              
>>> [<0000000040471028>] scsi_request_fn+0xf8/0xa90                                
>>> [<0000000040357244>] __blk_run_queue+0x4c/0x70                                 
>>> [<00000000403802c4>] cfq_insert_request+0x2dc/0x580                            
>>> [<0000000040356404>] __elv_add_request+0x1b4/0x300                             
>>>
>>> We have in blk-merge.c:
>>>
>>>               else {
>>>                       /*
>>>                        * If the driver previously mapped a shorter
>>>                        * list, we could see a termination bit
>>>                        * prematurely unless it fully inits the sg
>>>                        * table on each mapping. We KNOW that there
>>>                        * must be more entries here or the driver
>>>                        * would be buggy, so force clear the
>>>                        * termination bit to avoid doing a full
>>>                        * sg_init_table() in drivers for each command.
>>>                        */
>>>                       if (sg_is_last (*sg))
>>>                         printk ("__blk_segment_map_sg: clearing termination bi
>>> t\n");
>>>                       sg_unmark_end(*sg);
>>>                       *sg = sg_next(*sg);
>>>                       BUG_ON (!*sg);
>>>               }
>>>
>>> The comment suggests there must be more entries...
>>
>> I'm thinking with the split the scsi driver needs to provide one or two extra entires in the sg list.
> 
> 
> With the attached patch, I'm able to boot 4.2.0-rc2+ on linux-block at commit
> 54efd50bfd873e2dbf784e0b21a8027ba4299a3e.
> 
> I didn't try to optimize the number of extra entries but I know one is not enough.
> 
> I guess the puzzle is why the number of entries isn't calculated correctly in the first place.
> Further, why does blk-merge believe that it's okay to go beyond the terminator?  Clearly,
> the magic number isn't always set, etc.
> 
> I added the WARN_ON so I'd know when we run off the end of the the list.

Still fails to boot for me on c3000 
(although I think the patch is going into the right direction!):

[   25.140000] cdrom: Uniform CD-ROM driver Revision: 3.20
[   25.200000] sd 3:0:6:0: [sdb] Write cache: disabled, read cache: enabled, supports DPO and FUA
[   25.304000] sd 3:0:5:0: [sda] Write cache: disabled, read cache: enabled, supports DPO and FUA
[   25.436000]  sdb: sdb1 sdb2 sdb3 < sdb5 sdb6 >
[   25.488000]  sda: sda1 sda2 sda3 < sda5 sda6 >
[   25.560000] sd 3:0:6:0: [sdb] Attached SCSI disk
[   25.636000] scsi_id(112): unaligned access to 0x00000000faad5009 at ip=0x000000004100390b
[   25.752000] sd 3:0:5:0: [sda] Attached SCSI disk
[   25.832000] scsi_id(113): unaligned access to 0x00000000fa90a009 at ip=0x000000004100390b
[   25.972000] ------------[ cut here ]------------
[   26.028000] WARNING: at /build/linux-4.4-neu/linux-4.4.2/block/blk-merge.c:466
[   26.116000] random: nonblocking pool is initialized
[   26.172000] Modules linked in: sr_mod cdrom sd_mod ata_generic ohci_pci ehci_pci ohci_hcd ehci_hcd pata_ns87415 libata sym53c8xx scsi_transport_spi usbcore scsi_modp
[   26.368000] CPU: 0 PID: 65 Comm: systemd-udevd Not tainted 4.4.0-1-parisc64-smp #1 Debian 4.4.2-3
[   26.476000] task: 00000000bbd70b08 ti: 00000000bbea8000 task.ti: 00000000bbea8000
[   26.564000] 
[   26.584000]      YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
[   26.640000] PSW: 00001000000001001111111100001110 Not tainted
[   26.708000] r00-03  000000ff0804ff0e 00000000409e8380 00000000404f18f4 00000000bbea91e0
[   26.804000] r04-07  00000000409b2b80 0000000000000000 0000000000000000 000000000000001e

Helge