linux-kernel - Re: [PATCH] panic: add TAINT

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Date:	Tue, 24 Jun 2014 11:06:15 -0400
From:	Dave Jones <davej@...hat.com>
To:	Josh Hunt <johunt@...mai.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Baron, Jason" <jbaron@...mai.com>
Subject: Re: [PATCH] panic: add TAINT_SOFTLOCKUP

On Tue, Jun 24, 2014 at 09:22:20AM -0500, Josh Hunt wrote:
 
 > >> In addition to adding the softlockup taint flag, do you think it'd be
 > >> reasonable to add another flag for page allocation failures? I think
 > >> it'd be nice to be able to account for these conditions somehow without
 > >> having to parse dmesg, etc. As with the softlockup flag, it's helpful to
 > >> know if your system had encountered a page allocation failure at some
 > >> point before the crash or whatever you're debugging.
 > >
 > > I don't know, really.  Allocation failures are often an expected thing
 > > as drivers try to work out how much memory they can allocate.  Those
 > > things can be screened out by testing __GFP_NOWARN.  GFP_ATOMIC
 > > failures should probably be ignored, except for when they shouldn't.
 > > But even then, allocation failures are somewhat common.  And recency is
 > > a concern: an allocation failure 10 minutes ago is unlikely to be
 > > relevant.
 > >
 > > But that's just me waving hands around.  I'd be interested to hear from
 > > people whose kernels crash more often than mine, and from those whose
 > > job is to support them (ie distro people?).
 > >
 > 
 > Anyone you'd suggest adding to this thread to get other feedback about 
 > tracking page allocation failures? I could also spin up a patch and cc them.

For things like the fuzz test runs I do, I'd have to patch this out.

Things like migrate_pages() with bad arguments will trigger a page
allocation failure rather easily. Likewise set_mempolicy(), and a
handful of other vm syscalls.

There's also the case of "too fragmented to satisfy contiguous multi-page
allocation" which I walk into from time to time (when the kernel manages
to survive a fuzz run long enough, which isn't that often).

	Dave

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