[DRBD-user] NULL deref at drbd_submit_peer_request

Jasmin J. jasmin at anw.at
Fri Feb 10 02:58:46 CET 2017

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


>>> When running a kind of system test (detach/attach loop in high system load),
> "Don't do that, then." :-)
> [wonders what real-world scenario that test is supposed to excercise]
He does a TEST to find hidden bugs!
In my practice as a Kernel developer for safety critical systems, I did such 
tests a lot for my drivers. You should be happy that someone does such kind of 
stress testing and don't make him look like a fool.
Such tests are an appropriate method, beside others, to find design problems or 
implementation errors.

Even if you think it is unlikely in a real world example, it may happen to what 
ever reason in real world anyway. Think of thousands of installations and of 
millions of hours your DRBD driver is used over the world. It then becomes less 
unlikely, because of simple statistics. I even have to cope with bit flips due 
to natural cosmic radiation in my daily business (mission critical systems for 
aero-space). They are also very unlikely.

And when you look to his next eMail, he found a possible not symmetrical 
execution of ref-count counting. That is a very common error in Linux Kernel 
development and can be avoided by strictly symmetrical function executions by 
design. But they are hard to debug and a test he did is a good method to find 
such errors.


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