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SubjectRe: [PATCH 2/2 -mm] fault-injection: lightweight code-coverage maximizer
On Mon, Nov 27, 2006 at 11:51:30PM -0800, Don Mullis wrote:
> Allow all non-unique call stacks, as judged by pushed sequence of EIPs,
> to be to be ignored as failure candidates.
>
> Upon keying in
> echo 1 >probability
> echo 3 >verbose
> echo -1 >times
> a few dozen stacks are printk'ed, then system responsiveness
> recovers to normal. Similarly, starting a non-trivial program
> will print a few stacks before responsiveness recovers.

What kind of test did you do?

> Intent is to make code-coverage-maximizing test lightweight, perhaps
> light enough to remain enabled during the course of the developer's
> interactive testing of new code.
>
> Enabled by default. (/debug/fail*/stacktrace-depth > 0)

This doesn't maximize code coverage. It makes fault-injector reject
any failures which have same stacktrace before.

So it should not be default.

> +static bool fail_uniquestack(struct fault_attr *attr)
> +{
> + u32 oldhash;
> + u32 newhash;
> + uint offset = 0;
> +
> + newhash = unique_stack_p(attr);
> +
> + for ( oldhash = newhash; oldhash != 0; offset++) {
> + oldhash = atomic_xchg(
> + &attr->uniquestack_hash_table[
> + (newhash+offset)%ARRAY_SIZE(attr->uniquestack_hash_table)],
> + oldhash);
> + if (oldhash == newhash)
> + return false;
> + if (offset >= ARRAY_SIZE(attr->uniquestack_hash_table)) {
> + printk(KERN_NOTICE
> + "FAULT_INJECTION: table overflow -- "
> + "fault injection disabled\n");
> + return false;
> + }
> + }

Updating array in this way is not safe (SMP or interrupt).

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