From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Coywolf Qi Hunt <coywolf@greatcn.org>
Cc: linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: [BUG FIX] [PATCH] fork_init() max_low_pfn fixes potential OOM bug on big highmem machine
Date: Tue, 29 Jun 2004 11:58:30 +0100 [thread overview]
Message-ID: <20040629115830.A24951@flint.arm.linux.org.uk> (raw)
In-Reply-To: <40E148EE.1090207@greatcn.org>; from coywolf@greatcn.org on Tue, Jun 29, 2004 at 06:48:14PM +0800
On Tue, Jun 29, 2004 at 06:48:14PM +0800, Coywolf Qi Hunt wrote:
> Russell King wrote:
> Actually there's physical DRAM offset: PHY_OFFSET, defined on ARM only.
> max_low_pfn happens to be the same as `num_lowpages'.
> These assignments seems illogical in naming. But just happen to let this
> patch work. Other platforms may still break.
That may be a bug actually. Looking at ll_rw_blk.c:
unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
if (bounce_pfn < blk_max_low_pfn) {
blk_max_low_pfn = max_low_pfn;
dma_addr are physical addresses, so bounce_pfn is referenced to a PFN0
equal to physical address 0. This implies that blk_max_low_pfn is
likewise, as is max_low_pfn.
> [coywolf@everest ~/linux-2.6.7/arch]$ grep max_low_pfn arm* -rn
> arm/mm/init.c:235: max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
However, here, max_low_pfn of zero corresponds with the PFN of
PHYS_OFFSET. We have something with two different origins being
compared, which is nonsense. So something is wrong somewhere,
and my money is on max_low_pfn.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
next prev parent reply other threads:[~2004-06-29 10:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-28 15:55 [BUG FIX] [PATCH] fork_init() max_low_pfn fixes potential OOM bug on big highmem machine Coywolf Qi Hunt
2004-06-28 16:53 ` Russell King
2004-06-29 10:48 ` Coywolf Qi Hunt
2004-06-29 10:58 ` Russell King [this message]
2004-06-30 9:56 ` [BUG FIX] [ARM/ARM26] find_memend_and_nodes bug fix Coywolf Qi Hunt
2004-06-29 11:11 ` [BUG FIX] [PATCH] fork_init() max_low_pfn fixes potential OOM bug on big highmem machine Chris Wedgwood
2004-06-30 10:43 ` [BUG FIX] fork_init() " Coywolf Qi Hunt
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