Date: Sun, 9 Jan 2005 01:45:19 -0800
From: Andrew Morton <akpm@osdl.org>
To: Chris Wright <chrisw@osdl.org>
Cc: clameter@sgi.com, linux-kernel@vger.kernel.org
Subject: Re: panic on bootup due to __GFP_ZERO patch
Message-Id: <20050109014519.412688f6.akpm@osdl.org>
In-Reply-To: <20050108010629.M469@build.pdx.osdl.net>
References: <20050108010629.M469@build.pdx.osdl.net>
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Chris Wright <chrisw@osdl.org> wrote:
>
> I'm getting a panic during pidmap_init with a backtrace that looks
> something like:
> 
> buffered_rmqueue
> __alloc_pages
> get_zeroed_page
> pidmap_init
> start_kernel
> 
> Reverting the __GFP_ZERO patch fixes the issue, haven't drilled down
> any deeper yet to see what in the patch is causing the problem.  This is
> x86 w/out HIGHMEM (and no NUMA).
> 

Well it's doing clear_highpage() before __alloc_pages() has called
kernel_map_pages(), so CONFIG_DEBUG_PAGEALLOC is quite kaput.

So the current __GFP_ZERO buglist is:

1: Breaks CONFIG_DEBUG_PAGEALLOC

2: Breaks the cache aliasing protection for anonymous pages

3: prep_zero_page() uses KM_USER0 so __GFP_ZERO from IRQ context will
   cause rare memory corruption.

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