linux-kernel - Re: [2.6.27.24] Kernel coredump to a pipe is failing

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Message-ID: <20090527073136.GT846@one.firstfloor.org>
Date:	Wed, 27 May 2009 09:31:36 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, paul@...-scientist.net,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6.27.24] Kernel coredump to a pipe is failing

On Tue, May 26, 2009 at 05:29:35PM -0700, Andrew Morton wrote:
> On Wed, 27 May 2009 02:11:04 +0200 Andi Kleen <andi@...stfloor.org> wrote:
> 
> > > I dunno.  Is this true of all linux filesystems in all cases?  Maybe.
> > 
> > Assuming one of them is not would you rather want to fix that file system
> > or 10 zillion user programs (including the kernel core dumper) that 
> > get it wrong? @)
> > 
> 
> I think that removing one bug is better than adding one.
> 
> Many filesystems will return a short write if they hit a memory
> allocation failure, for example.  pipe_write() sure will.  Retrying
> is appropriate in such a case.

Sorry but are you really suggesting every program in the world that uses
write() anywhere should put it into a loop? That seems just like really
bad API design to me, requiring such contortions in a fundamental
system call just to work around kernel deficiencies.

I can just imagine the programmers putting nasty comments
about the Linux kernel on top of those loops and they would
be fully deserved.

And the same applies to in-kernel users really.

The memory allocation case more sounds like a bug in these fs and
in pipe.

e.g. the network stack sleeps waiting for memory, perhaps these
file systems should too.

Or it should just always return -ENOMEM. Typically when the 
system is badly out of memory you're gonna lose anyways because
a lot of things start failing.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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