mm: Don't offset memmap for flatmem]

----- Forwarded message from Laura Abbott <lauraa@codeaurora.org> -----

Date: Fri, 13 Mar 2015 17:08:35 -0700
From: Laura Abbott <lauraa@codeaurora.org>
To: Vlastimil Babka <vbabka@suse.cz>, Srinivas Kandagatla <srinivas.kandagatla@linaro.org>, linux-arm-kernel@lists.infradead.org, Russell King - ARM Linux
	<linux@arm.linux.org.uk>, ssantosh@kernel.org, Andrew Morton <akpm@linux-foundation.org>
Cc: Kevin Hilman <khilman@linaro.org>, Laura Abbott <lauraa@codeaurora.org>, Arnd Bergman <arnd@arndb.de>, Stephen Boyd <sboyd@codeaurora.org>,
	linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>, Kumar Gala <galak@codeaurora.org>
Subject: [PATCHv3] mm: Don't offset memmap for flatmem
X-Mailer: git-send-email 1.8.2.1

Srinivas Kandagatla reported bad page messages when trying to
remove the bottom 2MB on an ARM based IFC6410 board

BUG: Bad page state in process swapper  pfn:fffa8
page:ef7fb500 count:0 mapcount:0 mapping:  (null) index:0x0
flags: 0x96640253(locked|error|dirty|active|arch_1|reclaim|mlocked)
page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
bad because of flags:
flags: 0x200041(locked|active|mlocked)
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00007-g412f9ba-dirty #816
Hardware name: Qualcomm (Flattened Device Tree)
[<c0218280>] (unwind_backtrace) from [<c0212be8>] (show_stack+0x20/0x24)
[<c0212be8>] (show_stack) from [<c0af7124>] (dump_stack+0x80/0x9c)
[<c0af7124>] (dump_stack) from [<c0301570>] (bad_page+0xc8/0x128)
[<c0301570>] (bad_page) from [<c03018a8>] (free_pages_prepare+0x168/0x1e0)
[<c03018a8>] (free_pages_prepare) from [<c030369c>] (free_hot_cold_page+0x3c/0x174)
[<c030369c>] (free_hot_cold_page) from [<c0303828>] (__free_pages+0x54/0x58)
[<c0303828>] (__free_pages) from [<c030395c>] (free_highmem_page+0x38/0x88)
[<c030395c>] (free_highmem_page) from [<c0f62d5c>] (mem_init+0x240/0x430)
[<c0f62d5c>] (mem_init) from [<c0f5db3c>] (start_kernel+0x1e4/0x3c8)
[<c0f5db3c>] (start_kernel) from [<80208074>] (0x80208074)
Disabling lock debugging due to kernel taint

Removing the lower 2MB made the start of the lowmem zone to no longer
be page block aligned. IFC6410 uses CONFIG_FLATMEM where
alloc_node_mem_map allocates memory for the mem_map. alloc_node_mem_map
will offset for unaligned nodes with the assumption the pfn/page
translation functions will account for the offset. The functions for
CONFIG_FLATMEM do not offset however, resulting in overrunning
the memmap array. Just use the allocated memmap without any offset
when running with CONFIG_FLATMEM to avoid the overrun.

Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Reported-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>