From the 01408c4939 log message:
The problem is that when we write to a file, the copy from userspace to
pagecache is first done with preemption disabled, so if the source
address is not immediately available the copy fails *and* *zeros* *the*
*destination*.
This is a problem because a concurrent read (which admittedly is an odd
thing to do) might see zeros rather that was there before the write, or
what was there after, or some mixture of the two (any of these being a
reasonable thing to see).
If the copy did fail, it will immediately be retried with preemption
re-enabled so any transient problem with accessing the source won't
cause an error.
The first copying does not need to zero any uncopied bytes, and doing
so causes the problem. It uses copy_from_user_atomic rather than
copy_from_user so the simple expedient is to change copy_from_user_atomic
to *not* zero out bytes on failure.
< --- end cite --- >
This patch finally implements at least a not so pretty solution by
duplicating the relevant part of __copy_user.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Prefetching may be fatal on some systems if we're prefetching beyond the
end of memory on some systems. It's also a seriously bad idea on non
dma-coherent systems.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Removed obsolete stuff from arch makefile.
mips had a special rule for generating asm-offsets.h so preserved it
using an architecture specific hook in top-level Kbuild file.
Renamed .h file to asm-offsets.h
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Ralf Baechle