Messages in this thread |  | | | Subject | Breakage caused by unreviewed patch in x86 tree | | From | James Bottomley <> | | Date | Sun, 27 Apr 2008 16:51:25 -0400 |
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This patch:
commit 6371b495991debfd1417b17c2bc4f7d7bae05739 Author: Ingo Molnar <mingo@elte.hu> Date: Wed Jan 30 13:33:40 2008 +0100
x86: change ioremap() to default to uncached
As far as I can tell went blindly into the x86 tree without being shared on any mailing list at all. How can something that completely alters the semantics of ioremap on x86 platforms go in without any review.
I'm pissed off because it broke a class of voyager machines: those which rely on the quad interrupt controller (QIC). The precis of why they broke is because the QIC does IPIs (or CPIs in its terminology) via cache line interference: you interrupt a processor by moving a designated memory area to write exclusive in the cache (by simply writing to the line) and the CPU acks the interrupt by moving it back to read shared (by reading from it). That area, is, of course, mapped by ioremap, so reversing the ioremap semantics and adding the uncached bit completely breaks the QIC. I might add that the intel SAPIC functions in roughly the same manner, so this might break more than just voyager.
This patch was originally proposed my Matthew Wilcox in March 2006:
http://lkml.org/lkml/2006/3/30/251
And after a reasonable discussion, it was decided that there was too much risk of breakage to take it. How come you two decided that an identical patch with different authorship could go in to your tree without discussion this time?
James
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