Messages in this thread |  | | From | Neil Brown <> | Date | Fri, 2 Feb 2007 17:29:06 +1100 | Subject | Re: [rfc][patch] mm: half-fix page tail zeroing on write problem |
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On Friday February 2, npiggin@suse.de wrote: > Hi, > > For no important reason, I've again looked at those zeroing patches that > Neil did a while back. I've always thought that a simple > `write(fd, NULL, size)` would cause the same sorts of problems.
Yeh, but who in their right mind would do that??? Oh, you did :-)
> > Turns out it does. If you first write all 1s into a page, then do the > `write(fd, NULL, size)` at the same position, you end up with all 0s in > the page (test-case available on request). Incredible; surely this > violates the spec?
Does it? I guess filling with zeros isn't what one would expect, but you could make a case for it being right. write(fd, 0, size) writes 'size' 0s. Cool. Ok, bad-cool.
> > The buffered-write fixes I've got actually fix this properly, but they > don't look like getting merged any time soon. We could do this simple > patch which just reduces the chance of corruption from a certainty down > to a small race. > > Any thoughts?
I cannot see why you make a change to fault_in_pages_writeable. Is it just for symmetry? For the rest, it certainly makes sense to return an early -EFAULT if you cannot fault in the page.
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