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authorHeiko Carstens <heiko.carstens@de.ibm.com>2019-10-28 13:03:27 +0300
committerVasily Gorbik <gor@linux.ibm.com>2019-10-31 19:26:48 +0300
commit3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f (patch)
tree7b086d413d56374438633850d74f14bf82846581 /security
parenta1d863ac3e1085e1fea9caafd87252d08731de2e (diff)
downloadlinux-3d7efa4edd07be5c5c3ffa95ba63e97e070e1f3f.tar.xz
s390/idle: fix cpu idle time calculation
The idle time reported in /proc/stat sometimes incorrectly contains huge values on s390. This is caused by a bug in arch_cpu_idle_time(). The kernel tries to figure out when a different cpu entered idle by accessing its per-cpu data structure. There is an ordering problem: if the remote cpu has an idle_enter value which is not zero, and an idle_exit value which is zero, it is assumed it is idle since "now". The "now" timestamp however is taken before the idle_enter value is read. Which in turn means that "now" can be smaller than idle_enter of the remote cpu. Unconditionally subtracting idle_enter from "now" can thus lead to a negative value (aka large unsigned value). Fix this by moving the get_tod_clock() invocation out of the loop. While at it also make the code a bit more readable. A similar bug also exists for show_idle_time(). Fix this is as well. Cc: <stable@vger.kernel.org> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'security')
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