linux-kernel - [PATCH] sh: get_user_pages_fast() must flush cache the way

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Date:	Thu, 28 Aug 2014 12:56:41 +0400
From:	Stas Sergeev <stsp@...t.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linux kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] sh: get_user_pages_fast() must flush cache the way

Hi Andrew, could you please apply?


-=-=-=-=-=-=-=-=-=# Don't remove this line #=-=-=-=-=-=-=-=-=-
This patch avoids fuse hangs on sh4 by flushing the cache on
get_user_pages_fast(). This is not necessary a good thing to do,
but get_user_pages() does this, so get_user_pages_fast() should too.

Please note the patch for mips arch that addresses the similar problem:
https://kernel.googlesource.com/pub/scm/linux/kernel/git/ralf/linux/+/linux-3.4.50%5E!/#F0
They basically simply disable get_user_pages_fast() at all, using a
fall-back to get_user_pages(). But my fix is different, it adds an
explicit cache flushes.

Signed-off-by: Stas Sergeev <stsp@...rs.sourceforge.net>
---
 arch/sh/mm/gup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/sh/mm/gup.c b/arch/sh/mm/gup.c
index bf8daf9..37458f3 100644
--- a/arch/sh/mm/gup.c
+++ b/arch/sh/mm/gup.c
@@ -105,6 +105,8 @@ static noinline int gup_pte_range(pmd_t pmd,
unsigned long addr,
         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
         page = pte_page(pte);
         get_page(page);
+        __flush_anon_page(page, addr);
+        flush_dcache_page(page);
         pages[*nr] = page;
         (*nr)++;
 
-- 
1.7.11.7

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