linux-kernel - Re: [2.6.22.6] nfsd: fh_verify() `malloc failure' with lots of free memory leads to NFS hang

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Message-ID: <20070918011257.GC2443@fieldses.org>
Date:	Mon, 17 Sep 2007 21:12:57 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Nix <nix@...eri.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [2.6.22.6] nfsd: fh_verify() `malloc failure' with lots of
	free memory leads to NFS hang

On Tue, Sep 18, 2007 at 12:54:07AM +0100, Nix wrote:
> The code which calls new_do_write() looks like this:
> 
> ,----[ libio/fileops.c:_IO_new_file_xsputn() ]
> |  if (do_write)
> |    {
> |      count = new_do_write (f, s, do_write);
> |      to_do -= count;
> |      if (count < do_write)
> |        return n - to_do;
> |    }
> `----
> 
> This code handles partial writes followed by errors by returning a
> suitable nonzero value, and immediate errors by returning -1.
> 
> In either case the buffer will have been filled as much as possible by
> that point, and will still be filled when (vf)printf() is next called.

OK, I'm a little lost at this point (what's n?  What's to_do?), but I'll
take your word for it.

I'd be kinda curious when exactly the behavior changed and why.

Also I suppose we should check which version of nfs-utils that fix is in
and make sure distributions are getting the fixed nfs-utils before they
get the new libc, or we're going to see this bug a lot....

> This behaviour is, IIRC, mandated by the C Standard: I can find no
> reference in the Standard to streams being flushed on error, only
> on fclose(), fflush(), or program termination.

OK!

Let me know if the problem's fixed.

--b.
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