Re: issue with ubi_wl_put_peb

[Nikhilesh Reddy <reddyn@codeaurora.org>]

On Wed 24 Aug 2016 01:48:29 PM PDT, Richard Weinberger wrote:
> Nikhilesh Reddy,
>
> On 23.08.2016 20:55, Nikhilesh Reddy wrote:
>> Hi
>>
>>
>> I am currently running into a hard to reproduce issue( takes upto a week to reproduce) with ubi_wl_put_peb.
>>
>> I would appreciate any help you can give me.
>>
>> In the following stack
>> -000|__list_del_entry()
>> -001|list_del()
>> -002|prot_queue_del()
>> -003|ubi_wl_put_peb()
>> -004|ubi_eba_unmap_leb()
>> -005|ubifs_leb_unmap()
>> -006|ubifs_gc_start_commit()
>> -007|do_commit()
>> -008|run_bg_commit(inline)
>> -008|ubifs_bg_thread()
>> -009|kthread()
>>
>> This issue was seen with CONFIG_DEBUG_LIST=y
>>
>> What we see is that the wl entry that is being put is not in the protection queue but seems to be in free/used trees.
>
> So, you trigger a list assert?
> Please share the kernel log.
>
>> In the code  below:
>> http://git.infradead.org/linux-ubifs.git/blob/HEAD:/drivers/mtd/ubi/wl.c#l1231
>>
>> We see that the the wl_entry is checked to be in used/scrub and erroneous trees .. and then it simply assumes that it is in the protection queue if it is not in any of the rb trees.
>>
>> There appears to be a race where the  wl_entry is being put before it actually has a chance to be inserted into the protection queue.
>>
>> This seems to occur when ubi_io_write_vid_hdr takes long to write the VID header.
>>
>>
>> I noticed that a check for a similar situation is http://git.infradead.org/linux-ubifs.git/blob/HEAD:/drivers/mtd/ubi/wl.c#l761
>>
>> Is the same check needed in the case of ubi_wl_put_peb as well?
>>
>> Can you please tell me if this sounds like a known issue?
>>
>> I am a little lost on when |ubi_eba_unmap_leb would be called before the PEB has a chance to be inserted into a another tree from the free tree.
>>
>> I would be grateful any pointers that you can give me so i can get to the root cause.
>
> Hmmmm, is Fastmap involved?
>
> Thanks,
> //richard

Hi
Actually  FASTMAP was not involved.
This issue is pretty hard to reproduce ... just had reports of one 
instance where this occured.
If i see it again i will try to get all the logs.

Thanks So much for your help

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
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