AW: Bug in mtd_get_device_size()?

[Velykokhatko, Sergey]

Hi Richard,

Thanks, I saw that definition and calculation formula. But it is ambiguous. Depending on what you take for basis for that 1024. If you take MTD size you get completely other result as for basis with whole chip size. In my interpretation of actual implementation the basis of whole chip size for this case is totally wrong since it brings limitations of minimum partition size driven with UBI (someone from you already listed this argument too). In my case I patched this thing in mtd_get_device_size(). I understand that patch is wrong for complete system in your interpretation. But I report you my problem case, listed you my arguments and you decide what to do. In "our" 3.8 Kernel I left my patch since now system works so as I expected. 

Thanks a lot,
Best regards,
Sergey



-----Ursprüngliche Nachricht-----
Von: Richard Genoud [mailto:richard.genoud at gmail.com] 
Gesendet: Freitag, 1. März 2013 09:11
An: Brian Norris
Cc: Velykokhatko, Sergey; linux-mtd at lists.infradead.org; linux-kernel at vger.kernel.org; artem.bityutskiy at linux.intel.com
Betreff: Re: Bug in mtd_get_device_size()?

2013/2/28 Brian Norris <computersforpeace at gmail.com>:
> + Richard
>
> On Thu, Feb 28, 2013 at 4:30 AM, Velykokhatko, Sergey 
> <Sergey.Velykokhatko at mcc-med.de> wrote:
>> I got today such case:
>>
>>       * Kernel 3.8
>>
>>       * We are using M29F2G16 NAND chip with 4096 blocks, each has 
>> 128k
>>
>>       * Configured with CONFIG_MTD_UBI_BEB_LIMIT=100
>
> This is your problem. See below for more comments.
>
>>       * Our rootfs partition contains 640 EBs
>>
>>       * At system start comes following error message:
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.375000] Creating 6 MTD
>> partitions on "atmel_nand":
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.375000]
>> 0x000000000000-0x000000020000 : "obsolete_bootstrap"
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.381000]
>> 0x000000020000-0x000000320000 : "kernel_a"
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.386000]
>> 0x000000320000-0x000000620000 : "kernel_b"
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.392000]
>> 0x000000620000-0x000005620000 : "rootfs_a"
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.399000]
>> 0x000005620000-0x00000a620000 : "rootfs_b"
>>
>> Feb 28 09:23:09 (none) kern.notice kernel: [    0.406000]
>> 0x00000a620000-0x000020000000 : "config_data"
>>
>> ...
>>
>>
>>
>> Feb 28 09:23:10 (none) kern.info kernel: [    0.546000] NET: Registered
>> protocol family 17
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.557000] UBI: attaching
>> mtd3 to ubi0
>>
>> Feb 28 09:23:10 (none) kern.info kernel: [    0.748000] usb 1-2: new
>> high-speed USB device number 2 using atmel-ehci
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.810000] UBI: scanning is
>> finished
>>
>> Feb 28 09:23:10 (none) kern.warn kernel: [    0.821000] UBI warning:
>> print_rsvd_warning: cannot reserve enough PEBs for bad PEB handling, 
>> reserved 115, need 400
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: attached mtd3
>> (name "rootfs_a", size 80 MiB) to ubi0
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: PEB size:
>> 131072 bytes (128 KiB), LEB size: 129024 bytes
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: min./max. I/O
>> unit sizes: 2048/2048, sub-page size 512
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: VID header
>> offset: 512 (aligned 512), data offset: 2048
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: good PEBs:
>> 640, bad PEBs: 0, corrupted PEBs: 0
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: user volume:
>> 1, internal volumes: 1, max. volumes count: 128
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: max/mean
>> erase counter: 399/202, WL threshold: 4096, image sequence number: 
>> 548304255
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.826000] UBI: available
>> PEBs: 0, total reserved PEBs: 640, PEBs reserved for bad PEB 
>> handling: 115
>>
>> Feb 28 09:23:10 (none) kern.notice kernel: [    0.827000] UBI: background
>> thread "ubi_bgt0d" started, PID 288
>>
>> UBI wanted to reserve 400 blocks on MTD with 640. Hm... During 
>> debugging I found that mtd_get_device_size() gives the size of whole 
>> flash memory back
>> (4096 blocks * 128kB). I guess that I found small error. With micro 
>> patch the problem seems to be corrected for my case
>
> Your patch is wrong, actually. mtd_get_device_size() should get "the 
> size of the entire flash chip", so if mtd is a partition, you *want* 
> to return the size of its 'master'.
>
> In fact, everything is behaving as expected (by the designers; not by 
> you). Because your BEB_LIMIT=100, you are reserving 100*size/1024 
> (that is 9.8% of your total size, or 400 blocks) in *every* partition.
> I don't see why you need that high of a limit, though. Check your NAND 
> data sheet, but the limit defaults reasonably to 20 (or, about 2%).
> That would reserve only 80 blocks on your system, and you would not 
> see these warnings/errors, since you already have 115 blocks reserved.
That's rigth !
There's also some documentation on how the overhead is calculated here :
http://www.linux-mtd.infradead.org/doc/ubi.html#L_overhead
and some more explanations a little bellow, in the "Reserved blocks for bad block handling" section

>
> You might want to read the comments in this commit:
>
> commit ba4087e956d336488c6df9dfca65d1e70cf480f1
> Author: Richard Genoud <richard.genoud at gmail.com>
> Date:   Tue Jul 10 18:23:41 2012 +0200
>
>     UBI: use the whole MTD device size to get bad_peb_limit
>
> It might be worth revisiting the conclusions of those arguments; it 
> essentially limits your partitions to a certain minimum size. But as 
> far as I can tell, the code works as documented.
>
> Brian



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