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[dm-devel] Re: Strange SIGSEGV problem around dmcrypt, evms and jfs

On Mon, 16 Oct 2006, Dave Kleikamp wrote:
On Mon, 2006-10-16 at 18:12 +0200, Grzegorz Kulewski wrote:
I was begining to play with dmcrypt, evms and jfs on one spare disk I
have (currently empty and only for tests). I produced some partitions with
evms and made volumes on them. Nothing strange, normal configuration. The
partition layout seems ok. Then I used dmcrypt mappings on top of two of
them to make encrypted swaps and swapon'ed them. Still everything was ok.
Then I tested different ciphers performance by doing dmcrypt mappings on
top of some other volume with different settings and dd'ed data from and
to them to test the speed. Then I choosen one cipher setup and and did the
final mapping and created and mounted  jfs on it. Then I copied one large
(like 4GB) file on it several times to make sure everything is ok. I
checked sha1sums and everything was indeed ok.

But then all big applications (firefox, oo2, acroread, ..., opera was the
notable exception) couldn't start being killed by SIGSEGVs out of nowhere.
I reproduced it two time already (after a clean reboot): today and
yesterday. Maybe someone knows what is happening? For me it looks like
something broken some kernel memory and the kernel started doing stupid
things. But nothing strange has shown in logs.

One time I couldn't even shut down the machine normally, only SysRQ-B
worked (shutdown scripts were probably killed too or something). Every
application works ok (and did so for at least a year) before I will start
playing with dmcrypt and jfs. I am not sure where exactly the problems
start but will be investigating it shortly.

I am rather sure that my hardware is ok. Everything was and is fine till I
will start doing these tests.

What were you running before?  jfs?  evms?  Is dm-crypt the only new
element?  Trying a different file system on the same partition should
give you an idea whether jfs is a factor or not.

On my main disk I am using ext3. Both dm-crypt and evms were not used. But evms was on and was detecting partitions and created it's mappings on booting. Also I played with dm-crypt some longer time ago but it was unused recently here.

On my testing disk I didn't use anything since it was in store not so long ago. But I tested jfs on it (without anything like dm* under) and it was working well.

BTW. Why booting my machine with with nearly all debuging on I
got the following. While I am nearly sure it is not the problem I am
writing about I will report it:

Oct 16 17:29:33 kangur [   74.485627] =============================================
Oct 16 17:29:33 kangur [   74.485767] [ INFO: possible recursive locking detected ]
Oct 16 17:29:33 kangur [   74.485840] ---------------------------------------------

This is caused by CONFIG_DEBUG_LOCKDEP.  This will show false positives
against code that hasn't been annotated for lockdep.  I know the jfs
code hasn't been annotated yet, and from the look of this, neither has
the device-mapper code.  You should disable that option, since I doubt
it would be very helpful in tracking down a segfault, even if the code
was properly annotated.  The lockdep code is primarily for detecting
possible opportunities for a deadlock.

Ok, I knew that it was caused by lockdep and what lockdep does, but I reported it since it was touching dm, just to be sure.


Grzegorz Kulewski

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