Re: 2.6.19 file content corruption on ext3



On Sun, 17 Dec 2006, Andrew Morton wrote:

From my quick reading, all callers of try_to_free_buffers() have already
unmapped the page from pagetables, and given that the reported ext3 corruption
happens on uniprocessor, non-preempt kernels, I doubt if this patch will fix
things.

Hmm. One possible explanation: maybe the page actually _did_ get unmapped
from the page tables, but got added back?

I don't think we lock the page when faulting it in (we want it to be
uptodate, but not necessarily locked). So assuming the pageout sequence
always _does_ follow the rule that it only does try_to_free_buffers() on
pages that aren't mapped, what actually protects them from not becoming
mapped (and dirtied) during that sequence?

So we should probably do a "wait_for_page()" in do_no_page()?

Or maybe only do it for write accesses (since we don't really care about
getting mapped readably)? If so, we need to do it in the write case of
do_no_page() _and_ in the do_wp_page() case. Hmm?

Linus
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