2.4.0-test10-pre6 TLB flush race in establish_pte

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  • 2.4.0-test10-pre6 TLB flush race in establish_pte
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steven pratt Oct. 30, 2000, 9:31 p.m. UTC
Back in April there were discussions about the race in establish_pte with
the flush_tlb before the set_pte.  Many options were discussed, but due in
part to a concern about S/390 having introduced the code, no patch ever
appeared.  I talked with Martin Schwidefsky of the S/390 Linux development
team and he said that:

>the establish_pte was in fact introduced because of Linux/390. We wanted
to use the special S/390 instruction ipte (invalidate page >table entry).
In the meantime we found out that we need a lot more changes to be able to
use this instruction, so we disabled it again. >Until we have a proper
patch you should revoke the establish_pte change if you found it to be
faulty. I too think there is a race >condition.

So while there may be a more elegant solution down the road, I would like
to see the simple fix put back into 2.4.  Here is the patch to essential
put the code back to the way it was before the S/390 merge.  Patch is
against 2.4.0-test10pre6.




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Comments

Andrea Arcangeli Oct. 31, 2000, 12:30 a.m. UTC | #1
On Mon, Oct 30, 2000 at 03:31:22PM -0600, Steve Pratt/Austin/IBM wrote:
> [..] no patch ever
> appeared. [..]

You didn't followed l-k closely enough as the strict fix was submitted two
times but it got not merged. (maybe because it had an #ifdef __s390__ that was
_necessary_ by that time?)

You can find the old and now useless patch here:

	ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.4/2.4.0-test5/tlb-flush-smp-race-1

Andrea
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steven pratt Oct. 31, 2000, 4:23 p.m. UTC | #2
Andrea Arcangeli wrote:
> 
> On Mon, Oct 30, 2000 at 03:31:22PM -0600, Steve Pratt/Austin/IBM wrote:
> > [..] no patch ever
> > appeared. [..]
> 
> You didn't followed l-k closely enough as the strict fix was submitted two
> times but it got not merged. (maybe because it had an #ifdef __s390__ that was
> _necessary_ by that time?)
> 
> You can find the old and now useless patch here:
> 
>ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.4/2.4.0-test5/tlb-flush-smp-race-1


I stand corrected, I missed this is my searching.  Hopefully this will
get in this time.

Steve
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Patch

--- linux/mm/memory.c    Fri Oct 27 15:26:14 2000
+++ linux-2.4.0-test10patch/mm/memory.c  Fri Oct 27 15:45:54 2000
@@ -781,8 +781,8 @@ 
  */
 static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
 {
-    flush_tlb_page(vma, address);
     set_pte(page_table, entry);
+    flush_tlb_page(vma, address);
     update_mmu_cache(vma, address, entry);
 }