Re: AW: AW: ext4 filesystem bad extent error review

[Eric Sandeen <sandeen@redhat.com>]

On 1/3/14, 12:45 PM, Juergens Dirk (CM-AI/ECO2) wrote:
> 
> On Thu, Jan 03, 2014 at 19:24, Eric Sandeen wrote
>>
>> On 1/3/14, 10:29 AM, Juergens Dirk (CM-AI/ECO2) wrote:
>>> So, I think there _might_ be a kernel bug, but it could be also a
>> problem
>>> related to the particular type of eMMC. We did not observe the same
>> issue
>>> in previous tests with another type of eMMC from another supplier,
>> but this
>>> was with an older kernel patch level and with another HW design.
>>>
>>> Regarding a possible kernel bug: Is there any chance that the invalid
>>> ee_len or ee_start are returned by, e.g., the block allocator ?
>>> If so, can we try to instrument the code to get suitable traces ?
>>> Just to see or to exclude that the corrupted inode is really written
>>> to the eMMC ?
>>
>> From your description it does sound possible that it's a kernel bug.
>> Adding testcases to the code to catch it before it hits the journal
>> might be helpful - but then maybe this is something getting overwritten
>> after the fact - hard to say.
>>
>> Can you share more details of the test you are running?  Or maybe even
>> the test itself?
> 
> Yes, for sure, we can. Weller, please provide additional details
> or corrections. 
> 
> In short:
> Basically we use an automated cyclic test writing many small 
> (some kBytes) files with CRC checksums for easy consistency check
> into a separate test partition. Files also contain meta information
> like filename,  sequence number and a random number to allow to identify 
> from block device image dumps, if we just see a fragment of an old
> deleted file or a still valid one. 
> 
> Each test loop looks like this:

0) mkfs the filesystem - with what options?  How big?

> 1) Boot the device after power on or reset
> 2) Do fsck -n BEFORE mounting
> 2 a) (optional) binary dump of the journal 
> 3) Mount test partition

Again with what options, if any?

> 4) File content check for all files from prev. loop
> 5) erase all files from previous loop
> 6) start writing hundreds/thousands of test files 
>     in multiple directories with several threads

I guess this is where we might need more details in order,
to try to recreate the failure, but perhaps
this is not a case where you can simply share the IO
generation utility...?

Thanks,
-Eric

> 7) after random time cut the power or do soft reset
> 
> If 2), 3), 4) or 5) fails, stop test.
> 
> We are running the test usually with kind of transaction
> safe handling, i.e. use fsync/rename, to avoid zero length files
> or file fragments.
> 
>>
>> I've used a test framework in the past to simulate resets w/o needing
>> to reset the box, and do many journal replays very quickly.  It'd be
>> interesting to run it using your testcase.
>>
>> Thanks,
>> -Eric
> 
> Mit freundlichen Grüßen / Best regards
> 
> Dirk Juergens
> 
> Robert Bosch Car Multimedia GmbH
> 

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