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author | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-12-18 10:53:12 +0000 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-12-20 15:09:13 +0000 |
commit | 3705ff6da538aff6dba535e2e9cbcbb9456d0d53 (patch) | |
tree | 348fcec2be9d41e1839686a6c03f0b5479d7e4f9 /Documentation/hwmon/adm1021 | |
parent | ed3768a8d9dc2d345d4f27eb44ee1e4825056c08 (diff) | |
download | blackbird-op-linux-3705ff6da538aff6dba535e2e9cbcbb9456d0d53.tar.gz blackbird-op-linux-3705ff6da538aff6dba535e2e9cbcbb9456d0d53.zip |
ARM: Fix subtle race in CPU pen_release hotplug code
There is a subtle race in the CPU hotplug code, where a CPU which has
been offlined can online itself before being requested, which results
in things going astray on the next online/offline cycle.
What happens in the normal online/offline/online cycle is:
CPU0 CPU3
requests boot of CPU3
pen_release = 3
flush cache line
checks pen_release, reads 3
starts boot
pen_release = -1
... requests CPU3 offline ...
... dies ...
checks pen_release, reads -1
requests boot of CPU3
pen_release = 3
flush cache line
checks pen_release, reads 3
starts boot
pen_release = -1
However, as the write of -1 of pen_release is not fully flushed back to
memory, and the checking of pen_release is done with caches disabled,
this allows CPU3 the opportunity to read the old value of pen_release:
CPU0 CPU3
requests boot of CPU3
pen_release = 3
flush cache line
checks pen_release, reads 3
starts boot
pen_release = -1
... requests CPU3 offline ...
... dies ...
checks pen_release, reads 3
starts boot
pen_release = -1
requests boot of CPU3
pen_release = 3
flush cache line
Fix this by grouping the write of pen_release along with its cache line
flushing code to ensure that any update to pen_release is always pushed
out to physical memory.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'Documentation/hwmon/adm1021')
0 files changed, 0 insertions, 0 deletions