On Sun, 11 Apr 2010, Helge Deller wrote:
> Nevertheless, I still see the crashes with all kernel patches applied.
>
> What I usually do is to start up more than 8 screen sessions. In each of the
> sessions I start the bash loop:
> -> i=0; while true; do i=$(($i+1)); echo Run $i; ./minifail; done;
> and detach from the screen sessions.
> After some time, the load goes up to 8-16 and a few crashes fill the syslog.
> I'm sure the crashes are related to how much load the machine is, and how
> often process switches will happen.
> How many minifail testcases do you run in parallel?
Sigh, never more than one...
That said, I did realize last night that the cache flush in ptep_set_wrprotect
based on pte_dirty was flawed. In a SMP kernel with a user on a different
cpu pounding on the page to be write protected, there was a race between
the pte_dirty check and the write protect.
Further, I don't believe the dirty bit is reliable. Our cmpxchg is not
atomic with respect to changes in the dirty bit. Thus, there is a small
window where a change in the dirty bit could get lost.
So for now, I think it safest to move the flush after the setting of the
write protect bit, and do it unconditionally. This should be ok since
page faults are disabled. I recognize that this will hurt performance.
I'm going to test the following on my rp3440. The flushing has greatly
improved SMP userspace stability. However, I have still seen a few issues
in the GCC testsuite.
Maybe it will help your B2000. However, let's just go one step at a time.
Dave
--
J. David Anglin dave.anglin@xxxxxxxxxxxxxx
National Research Council of Canada (613) 990-0752 (FAX: 952-6602)
diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index a27d2e2..e85f43c 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -14,6 +14,7 @@
#include <linux/bitops.h>
#include <asm/processor.h>
#include <asm/cache.h>
+extern void flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr, unsigned long pfn);
/*
* kern_addr_valid(ADDR) tests if ADDR is pointing to valid kernel
@@ -456,7 +457,7 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
return old_pte;
}
-static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
+static inline void ptep_set_wrprotect(struct vm_area_struct *vma, struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
#ifdef CONFIG_SMP
unsigned long new, old;
@@ -469,6 +470,8 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
pte_t old_pte = *ptep;
set_pte_at(mm, addr, ptep, pte_wrprotect(old_pte));
#endif
+
+ flush_cache_page(vma, addr, pte_pfn(*ptep));
}
#define pte_same(A,B) (pte_val(A) == pte_val(B))
--
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