On 5/14/2014 3:12 PM, Helge Deller wrote:
On 05/14/2014 05:31 AM, Carlos O'Donell wrote:
On Sun, May 11, 2014 at 6:40 PM, John David Anglin <dave.anglin@xxxxxxxx> wrote:
2) Removes the lock code on UP systems where it is not needed, and
This is wrong. The locking was originally only for SMP, but at one
point it was discovered that you could COW during the CAS operation
and if you didn't take the lock in UP, you could re-enter the CAS via
another task and thus incorrectly carry out the CAS in two different
threads and corrupt the state. While we attempt our best to prevent
the task running the CAS from being scheduled off, the COW operation
trap and subsequent scheduling is not something I could find an easy
way to prevent. Therefore the solution was to use locks for both UP
and SMP.
If so, could one of you please send an updated patch to the list...?
Currently I've scheduled http://git.kernel.org/cgit/linux/kernel/git/deller/parisc-linux.git/commit/?h=for-next&id=f4030047d92c79344ac4ca6ad4c6e3e22ceb5a55
for inclusion into the next kernel (hopefully 3.15).
I agree that a COW could occur but I haven't seen evidence that threads are
getting rescheduled. We did fix some code in the fault handling a few
months
ago. Anyway, I have no strong objection to removing ifdefs and
resending after
testing.
Dave
--
John David Anglin dave.anglin@xxxxxxxx
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