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Date:   Fri, 27 Apr 2018 06:20:16 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Michal Hocko <mhocko@kernel.org>
cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        John Stoffel <john@stoffel.org>,
        James Bottomley <James.Bottomley@HansenPartnership.com>,
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        jasowang@redhat.com, Randy Dunlap <rdunlap@infradead.org>,
        linux-kernel@vger.kernel.org, Matthew Wilcox <willy@infradead.org>,
        linux-mm@kvack.org, dm-devel@redhat.com,
        Vlastimil Babka <vbabka@suse.cz>, Andrew@stoffel.org,
        David Rientjes <rientjes@google.com>,
        Morton <akpm@linux-foundation.org>,
        virtualization@lists.linux-foundation.org,
        David Miller <davem@davemloft.net>, edumazet@google.com
Subject: Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback
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On Fri, 27 Apr 2018, Michal Hocko wrote:

> On Thu 26-04-18 18:52:05, Mikulas Patocka wrote:
> > 
> > 
> > On Fri, 27 Apr 2018, Michael S. Tsirkin wrote:
> [...]
> > >    But assuming it's important to control this kind of
> > >    fault injection to be controlled from
> > >    a dedicated menuconfig option, why not the rest of
> > >    faults?
> > 
> > The injected faults cause damage to the user, so there's no point to 
> > enable them by default. vmalloc fallback should not cause any damage 
> > (assuming that the code is correctly written).
> 
> But you want to find those bugs which would BUG_ON easier, so there is a
> risk of harm IIUC

Yes, I want to harm them, but I only want to harm the users using the 
debugging kernel. Testers should be "harmed" by crashes - so that the 
users of production kernels are harmed less.

If someone hits this, he should report it, use the kernel parameter to 
turn it off and continue with the testing.

> and this is not much different than other fault injecting paths.

Fault injections causes misbehavior even on completely bug-free code (for 
example, syscalls randomly returning -ENOMEM). This won't cause 
misbehavior on bug-free code.

Mikulas