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Date: Fri, 13 Jul 2018 16:58:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: Instability in current -git tree
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Matthew Wilcox <willy@infradead.org>, Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, David Miller <davem@davemloft.net>, Al Viro <viro@zeniv.linux.org.uk>, Dave Airlie <airlied@gmail.com>, Tejun Heo <tj@kernel.org>, Ted Ts'o <tytso@google.com>, Mike Snitzer <snitzer@redhat.com>, linux-mm <linux-mm@kvack.org>, Daniel Vacek <neelx@redhat.com>, Pavel Tatashin <pasha.tatashin@oracle.com>, Mel Gorman <mgorman@techsingularity.net>

On Fri, 13 Jul 2018 16:51:39 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Fri, Jul 13, 2018 at 4:48 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > (But it would be interesting to see whether removing the check "fixes" it)
> 
> I'm building a "replace VM_BUG_ON() with proper printk's instead" right now.
> 
> Honestly, I think VM_BUG_ON() is complete garbage to begin with. We
> know the code can't depend on it, since it's only enabled for VM
> developers. And if it ever triggers, it doesn't get logged because the
> machine is dead (since the VM code almost always holds critical
> locks). So it's exactly the worst kind of BUG_ON.
> 
> Can we turn VM_BUG_ON() into "WARN_ON_ONCE()" and be done with it? The
> VM developers will actually get better reports, and non-vm-developers
> don't have dead machines.
> 

OK by me.  I don't recall ever thinking "gee, I wish the machine had
crashed at this point".

However we shouldn't simply blunder on in the presence of possible
memory corruption so a conversion would need to be done carefully.