On Fri, 20 Oct 2006, David Miller wrote:
>
> I did some more digging, here's what I think the hardware actually
> does:
Ok, this sounds sane.
What should we do about this? How does this patch look to people?
(Totally untested, and I'm not sure we should even do that whole
"oldmm->mm_users" test, but I'm throwing it out here for discussion, in
case it matters for performance. The second D$ flush should obviously be
unnecessary for the common unthreaded case, which is why none of this has
mattered historically, I think).
Comments? We need ARM, MIPS, sparc and S390 at the very least to sign off
on this, and somebody to write a nice explanation for the changelog (and
preferably do this through -mm too).
Linus
---
diff --git a/kernel/fork.c b/kernel/fork.c
index 29ebb30..14c6a1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -287,8 +287,18 @@ static inline int dup_mmap(struct mm_str
}
retval = 0;
out:
- up_write(&mm->mmap_sem);
flush_tlb_mm(oldmm);
+ /*
+ * If we have other threads using the old mm, we need to
+ * flush the D$ again - the other threads might have dirtied
+ * it more before the TLB got flushed.
+ *
+ * After the flush, they can no longer dirty more pages,
+ * since they are now marked read-only, of course.
+ */
+ if (atomic_read(&oldmm->mm_users) != 1)
+ flush_cache_mm(oldmm);
+ up_write(&mm->mmap_sem);
up_write(&oldmm->mmap_sem);
return retval;
fail_nomem_policy:
-
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