[linuxsh-dev] Re: "pte_clear" needed in copy_user_page? (was Re: System reset while INIT processing)

[SUGIOKA T. <su...@it...>]

At 10:55 01/07/17 +0900, Masahiro Abe <m-...@aa...> wrote:
>Current arch/sh/mm/cache.c in CVS gives me Oops error on our custom
>board, while INIT. (This doesn't happen on SolutionEngine 7750S.)
>
>Errors are "Unable to handle kernel paging request at virtual address
>c0000000", with address varies to c0001000/c0002000/c0003000. Errors
>occur at PC=8800c488, which is within __flush_dcache_region.
>
>copy_user_page and clear_user_page were modified to call pte_clear after
>copy_page/clear_page. If I comment this call out, then Oops errors
>disappear. (In fact, after comment out, the system is so stable so far
>that RTLinux is running reliably.)
>
>I still don't understand the reason of call to it, but I would like to
>know if it is necessary to call it or not. If it is, then what do you
>think I should do to kill this Oops error?

I hope that following patch will solve the problem.
I'm not so sure that this is absolutely correct, but it will be safe anyway.

Index: arch/sh/mm/cache.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/mm/cache.c,v
retrieving revision 1.43
diff -u -r1.43 cache.c
--- arch/sh/mm/cache.c	2001/07/16 05:08:19	1.43
+++ arch/sh/mm/cache.c	2001/07/17 03:06:10
@@ -553,9 +553,9 @@
 		__flush_tlb_page(get_asid(), p3_addr);
 		update_mmu_cache(NULL, p3_addr, entry);
 		clear_page((void *)p3_addr);
+		__flush_dcache_region(p3_addr, p3_addr+PAGE_SIZE);
 		pte_clear(pte);
 		restore_flags(flags);
-		__flush_dcache_region(p3_addr, p3_addr+PAGE_SIZE);
 	}
 }
 
@@ -592,9 +592,9 @@
 		__flush_tlb_page(get_asid(), p3_addr);
 		update_mmu_cache(NULL, p3_addr, entry);
 		copy_page((void *)p3_addr, from);
+		__flush_dcache_region(p3_addr, p3_addr+PAGE_SIZE);
 		pte_clear(pte);
 		restore_flags(flags);
-		__flush_dcache_region(p3_addr, p3_addr+PAGE_SIZE);
 	}
 }
 #endif

----
SUGIOKA Toshinobu