linux-kernel - Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback options

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Message-ID: <alpine.LRH.2.02.1804261451120.23716@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Thu, 26 Apr 2018 14:54:26 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
cc:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Michal Hocko <mhocko@...nel.org>,
        David Rientjes <rientjes@...gle.com>, dm-devel@...hat.com,
        eric.dumazet@...il.com, netdev@...r.kernel.org,
        jasowang@...hat.com, Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        linux-mm@...ck.org, edumazet@...gle.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        virtualization@...ts.linux-foundation.org,
        David Miller <davem@...emloft.net>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [dm-devel] [PATCH v5] fault-injection: introduce kvmalloc fallback
 options



On Thu, 26 Apr 2018, Michael S. Tsirkin wrote:

> On Thu, Apr 26, 2018 at 12:07:25PM -0400, Mikulas Patocka wrote:
> > > IIUC debug kernels mainly exist so people who experience e.g. memory
> > > corruption can try and debug the failure. In this case, CONFIG_DEBUG_SG
> > > will *already* catch a failure early. Nothing special needs to be done.
> > 
> > The patch helps people debug such memory coprruptions (such as using DMA 
> > API on the result of kvmalloc).
> 
> That's my point.  I don't think your patch helps debug any memory
> corruptions.  With CONFIG_DEBUG_SG using DMA API already causes a
> BUG_ON, that's before any memory can get corrupted.

The patch turns a hard-to-reproduce bug into an easy-to-reproduce bug. 

Obviously we don't want this in production kernels, but in the debug 
kernels it should be done.

Mikulas