linux-kernel - Re: [PATCH/v2] mm/memblock: Properly handle overlaps and fix error path

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Message-ID: <4D77E5E0.6010706@kernel.org>
Date:	Wed, 09 Mar 2011 12:41:04 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Russell King <linux@....linux.org.uk>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH/v2] mm/memblock: Properly handle overlaps and fix error
 path

On 03/06/2011 07:03 PM, Benjamin Herrenschmidt wrote:
> Currently memblock_reserve() or memblock_free() don't handle overlaps
> of any kind. There is some special casing for coalescing exactly
> adjacent regions but that's about it.
> 
> This is annoying because typically memblock_reserve() is used to
> mark regions passed by the firmware as reserved and we all know
> how much we can trust our firmwares...
> 
> Also, with the current code, if we do something it doesn't handle
> right such as trying to memblock_reserve() a large range spanning
> multiple existing smaller reserved regions for example, or doing
> overlapping reservations, it can silently corrupt the internal
> region array, causing odd errors much later on, such as allocations
> returning reserved regions etc...
> 
> This patch rewrites the underlying functions that add or remove a
> region to the arrays. The new code is a lot more robust as it fully
> handles overlapping regions. It's also, imho, simpler than the previous
> implementation.
> 
> In addition, while doing so, I found a bug where if we fail to double
> the array while adding a region, we would remove the last region of
> the array rather than the region we just allocated. This fixes it too.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
> 
> Hopefully not damaged with a spurious bit of email header this
> time around... sorry about that.

works on my setups...

[    0.000000] Subtract (26 early reservations)
[    0.000000]   [000009a000-000009efff]
[    0.000000]   [000009f400-00000fffff]
[    0.000000]   [0001000000-0003495048]
...
before:
[    0.000000] Subtract (27 early reservations)
[    0.000000]   [000009a000-000009efff]
[    0.000000]   [000009f400-00000fffff]
[    0.000000]   [00000f85b0-00000f86b3]
[    0.000000]   [0001000000-0003495048]

Acked-by: Yinghai Lu <yinghai@...nel.org>
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