> > > > > Like __block_prepare_write()?
quoted text
> > > > 
> > > > That's called with the page locked and page->mapping verified.
> > > 
> > > Only when called via standard codepath.
> > 
> > It would be a grave error to call it without the page lock.
> 
> Page is locked of course, but invalidated, removed from all trees and
> caches, i.e. grab, lock, check, unlock... invalidate, write into that
> page should fail, but it will not, since page is uptodate and
> prepare_write does not check mapping at all.

But callers do check after having locked the page.

quoted text
> > > Instead of returning error when reading from invalid page, now you
> > > return old content of it?
> > 
> > No, instead of returning a short count, it is now returning old
> > content.
> 
> Or instead of returning error or zero and relookup page eventually,
> which can already contain new data, we get old data.

Umm, it doesn't make any sense to try to always get fresh data.  If
you do read() on a file, the data may become old and invalid a
millisecond after the read finished.  We can't and needn't do anything
about this.

Miklos
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