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Commit b29c6ef7 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki Committed by Linus Torvalds
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x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu()



Even though aperfmperf_snapshot_khz() caches the samples.khz value to
return if called again in a sufficiently short time, its caller,
arch_freq_get_on_cpu(), still uses smp_call_function_single() to run it
which may allow user space to trigger an IPI storm by reading from the
scaling_cur_freq cpufreq sysfs file in a tight loop.

To avoid that, move the decision on whether or not to return the cached
samples.khz value to arch_freq_get_on_cpu().

This change was part of commit 941f5f0f ("x86: CPU: Fix up "cpu MHz"
in /proc/cpuinfo"), but it was not the reason for the revert and it
remains applicable.

Fixes: 4815d3c5 (cpufreq: x86: Make scaling_cur_freq behave more as expected)
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarWANG Chao <chao.wang@ucloud.cn>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 99306dfc
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