Re: [patch 0/7] fault-injection capabilities (v5)

[Akinobu Mita <akinobu.mita@gmail.com>]

On Thu, Oct 12, 2006 at 02:26:25PM -0700, Andrew Morton wrote:

> You've presumably run a kernel with these various things enabled.  What
> happens?  Does the kernel run really slowly?  Does userspace collapse in a
> heap?  Does it oops and die?

I don't feel much slowness with STACKTRACE & FRAME_POINTER and
enabling stacktrace filter. But with enabling STACK_UNWIND I feel
big latency on X. (There are two type of implementation of stacktrace
filter in it [1] using STACKTRACE with FRAME_POINTER, and [2] STACK_UNWIND)

I don't know why there is quite difference between simple STACKTRACE and
STACK_UNWIND. I'm about to try to use rb tree rather than linked list in
unwind.

In order to prevent from breaking other userspace programs and to
inject failures into only a specific code or process, process filter and
stacktrace filter are available. Without using them the system would be
almost unusable.

Now I'm stuck on the script in fault-injection.txt with random 700
modules. This script just tries to load/unload for all available kernel
modules. It usually get several oopses or CPU soft lockup now.  It
seems that relatively large number of them involved around driver model
(drivers/base/*). (I hope recent large number of error handle fixes
especially by Jeff Garzik fix them)

> Also, one place where this infrastructure could be of benefit is in device
> drivers: simulate a bad sector on the disk, a pulled cable, a timeout
> reading from a status register, etc.  If that works well and is useful then
> I can see us encouraging driver developers to wire up fault-injection in
> the major drivers.
> 
> Hence it would be useful at some stage to go in and to actually do all this
> for a particular driver.  As an example implementation for others to
> emulate and as a test for the fault-injection infrastructure itself - we
> may discover that new capabilities are needed as this work is done.
> 
> I wouldn't say this is an urgent thing to be doing, but it is a logical
> next step..

Yes. I'm learning from md/faulty and scsi-debug module what they are
doing and how to integrate such kind of features in general form.