s390 storage key inconsistency? [was Re: msync() behaviour brokenfor MS_ASYNC, revert patch?]

[Stephen C. Tweedie]

Hi,

On Thu, 2004-04-01 at 17:19, Jamie Lokier wrote:

> Some documentation I'm looking at says MS_INVALIDATE updates the
> mapped page to contain the current contents of the file.  2.6.4 seems
> to do the reverse: update the file to contain the current content of
> the mapped page.  "man msync" agrees with the the latter.  (I can't
> look at SUS right now).

btw, just looking at the filemap_sync_pte() code for MS_INVALIDATE, I
noticed

	if (!PageReserved(page) &&
	    (ptep_clear_flush_dirty(vma, address, ptep) ||
	     page_test_and_clear_dirty(page)))
		set_page_dirty(page);

I just happened to follow the function and noticed that on s390,
page_test_and_clear_dirty() has the comment:

* Test and clear dirty bit in storage key.
* We can't clear the changed bit atomically. This is a potential
* race against modification of the referenced bit. This function
* should therefore only be called if it is not mapped in any
* address space.

but in this case the page is clearly mapped in the caller's address
space, else we wouldn't have reached this.

Is this a problem?

--Stephen



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