Re: [PATCH] COMPACTION: bugfix of improper cache flush in MIGRATIONcode.

[Rik van Riel]

On 05/08/2013 08:18 PM, Leonid Yegoshin wrote:
> Page 'new' during MIGRATION can't be flushed by flush_cache_page().
> Using flush_cache_page(vma, addr, pfn) is justified only if
> page is already placed in process page table, and that is done right
> after flush_cache_page(). But without it the arch function has
> no knowledge of process PTE and does nothing.
>
> Besides that, flush_cache_page() flushes an application cache,
> kernel has a different page virtual address and dirtied it.
>
> Replace it with flush_dcache_page(new) which is a proper usage.
>
> Old page is flushed in try_to_unmap_one() before MIGRATION.
>
> This bug takes place in Sead3 board with M14Kc MIPS CPU without
> cache aliasing (but Harvard arch - separate I and D cache)
> in tight memory environment (128MB) each 1-3days on SOAK test.
> It fails in cc1 during kernel build (SIGILL, SIGBUS, SIGSEG) if
> CONFIG_COMPACTION is switched ON.

Good catch!

> Author: Leonid Yegoshin <yegoshin@xxxxxxxx>
> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@xxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>

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