timex: filter unreasonable offset values from kernel adjtimex() overflow - #3766
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dongjiang1989 wants to merge 1 commit into
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timex: filter unreasonable offset values from kernel adjtimex() overflow#3766dongjiang1989 wants to merge 1 commit into
dongjiang1989 wants to merge 1 commit into
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On KVM/pvclock guests, a race condition in the kernel NTP PLL can cause adjtimex() to return 2^32 ns (4.294967296s) as a transient overflow value, triggering false-positive NodeClockSkewDetected alerts hundreds of times per day despite NTP being correctly synchronized. Add a ±1.0s sanity bound in the timex collector: values exceeding this threshold are discarded (set to 0) with a warning log, as real NTP sync never produces offsets of this magnitude. Apply the same bound in the NodeClockSkewDetected alert expression to provide defense-in-depth at the rule layer. Fixes prometheus#3764 Signed-off-by: dongjiang <dongjiang1989@126.com>
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Summary
Fixes #3764
On KVM/pvclock guests, a race condition in the kernel NTP PLL can cause
adjtimex()to return2^32 ns(4.294967296s) as a transient overflow value, triggering false-positiveNodeClockSkewDetectedalerts hundreds of times per day despite NTP being correctly synchronized.This PR applies defense-in-depth at two layers:
collector/timex.go): values exceeding ±1.0s are discarded (set to 0) with a warning log. Real NTP synchronization never produces offsets of this magnitude.docs/node-mixin/alerts/alerts.libsonnet):NodeClockSkewDetectedexpression gains an upper bound check (< 1.0/> -1.0) so the overflow artifact no longer passes the threshold filter even if the collector still emits it.Why ±1.0s?
MAXPHASEin the kernel is 500ms