On Thu, 8 Feb 2007, Nick Piggin wrote:
> Still no independent confirmation as to whether this is a problem or not.
I'm trying to convince myself none of your patch is necessary. Probably
shall fail. But how come we've survived for years with such an issue?
> Updated some comments, added diffstats to patches, don't use
> __SetPageUptodate as an internal page-flags.h private function.
Depressed by profusion of PageUptodate_UpperAndlowercasevariants.
Those rmbs, you really only want them when it says "yes", don't you?
>
> I would like to eventually get an ack from Hugh regarding the anon memory
> and especially swap side of the equation,
Plea noted. I'm pondering. "Eventually" indeed. OTOH I expect you're
right to criticize anon/swap PageUptodate being set where it was needed
to get by, rather than where it was natural to do so.
> and a glance from whoever put the
> smp_wmb()s into the copy functions (Was it Ben H or Anton maybe?)
From: Linus Torvalds <[email protected]>
Date: Thu, 14 Oct 2004 04:00:06 +0000 (-0700)
Subject: Fix threaded user page write memory ordering
X-Git-Tag: v2.6.9-final~3
X-Git-Url: http://127.0.0.1:1234/?p=.git;a=commitdiff_plain;h=538ce05c0ef4055cf29a92a4abcdf139d180a0f9;hp=8c225dbc5a7b13801a8254aae0ccebab8e4bece7
Fix threaded user page write memory ordering
Make sure we order the writes to a newly created page
with the page table update that potentially exposes the
page to another CPU.
This is a no-op on any architecture where getting the
page table spinlock will already do the ordering (notably
x86), but other architectures can care.
---
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 232d8fd..7153aef 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -40,6 +40,8 @@ static inline void clear_user_highpage(s
void *addr = kmap_atomic(page, KM_USER0);
clear_user_page(addr, vaddr, page);
kunmap_atomic(addr, KM_USER0);
+ /* Make sure this page is cleared on other CPU's too before using it */
+ smp_wmb();
}
static inline void clear_highpage(struct page *page)
@@ -73,6 +75,8 @@ static inline void copy_user_highpage(st
copy_user_page(vto, vfrom, vaddr, to);
kunmap_atomic(vfrom, KM_USER0);
kunmap_atomic(vto, KM_USER1);
+ /* Make sure this page is cleared on other CPU's too before using it */
+ smp_wmb();
}
static inline void copy_highpage(struct page *to, struct page *from)
-
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