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Re: 2.6.24-rc2 crash in kmap_coherent

To: Florian Lohoff <flo@rfc822.org>
Subject: Re: 2.6.24-rc2 crash in kmap_coherent
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 12 Dec 2007 15:32:18 +0000
Cc: linux-mips@linux-mips.org, David Daney <ddaney@avtrex.com>
In-reply-to: <20071212120610.GB28868@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20071211221327.GB2150@paradigm.rfc822.org> <20071212120610.GB28868@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.17 (2007-11-01)
On Wed, Dec 12, 2007 at 12:06:10PM +0000, Ralf Baechle wrote:

> > Call Trace:
> > [<ffffffff8801bcf0>] kmap_coherent+0x10/0x130
> > [<ffffffff8801c010>] copy_from_user_page+0x40/0xb0
> > [<ffffffff88079d10>] access_process_vm+0x168/0x1d8
> > [<ffffffff880d9014>] proc_pid_cmdline+0xac/0x140
> > [<ffffffff880db188>] proc_info_read+0x108/0x150
> > [<ffffffff8808fbdc>] vfs_read+0xec/0x178
> > [<ffffffff88090060>] sys_read+0x50/0x98
> > [<ffffffff88019718>] handle_sys+0x118/0x134
> > 
> > 
> > Code: 0002127a  00021000  30420001 <00028036> 8f820024  3c038843  24420001  
> > af820024  dc62f390 
> 
> Hmm...  This suggests that 283abbaef425c1bf817ecbb456c413cab08b1434 is
> not quite right.  It is making the assumption that a mapped page never has
> PG_dcache_dirty set.

Totally untested because I have other stuff to do but something along the
lines of below patch, I think.

  Ralf

diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 480dec0..db5d608 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -211,7 +211,8 @@ void copy_user_highpage(struct page *to, struct page *from,
        void *vfrom, *vto;
 
        vto = kmap_atomic(to, KM_USER1);
-       if (cpu_has_dc_aliases && page_mapped(from)) {
+       if (cpu_has_dc_aliases &&
+           page_mapped(from) && !Page_dcache_dirty(from)) {
                vfrom = kmap_coherent(from, vaddr);
                copy_page(vto, vfrom);
                kunmap_coherent();
@@ -234,7 +235,8 @@ void copy_to_user_page(struct vm_area_struct *vma,
        struct page *page, unsigned long vaddr, void *dst, const void *src,
        unsigned long len)
 {
-       if (cpu_has_dc_aliases && page_mapped(page)) {
+       if (cpu_has_dc_aliases &&
+           page_mapped(page) && !Page_dcache_dirty(from)) {
                void *vto = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
                memcpy(vto, src, len);
                kunmap_coherent();
@@ -253,7 +255,8 @@ void copy_from_user_page(struct vm_area_struct *vma,
        struct page *page, unsigned long vaddr, void *dst, const void *src,
        unsigned long len)
 {
-       if (cpu_has_dc_aliases && page_mapped(page)) {
+       if (cpu_has_dc_aliases &&
+           page_mapped(page) && !Page_dcache_dirty(page)) {
                void *vfrom = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
                memcpy(dst, vfrom, len);
                kunmap_coherent();

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