When bidirectional keep-alive is enabled (both client and server
sending keep-alive pings), the server incorrectly validates ping
acknowledgments (ACKs) sent in response to server-initiated pings.
This causes the KeepAliveEnforcer strike counter to increment for
legitimate protocol responses, eventually triggering a GO_AWAY with
ENHANCE_YOUR_CALM.

Move the keepAliveEnforcer.pingAcceptable() check inside the !ack
conditional block, so only client-initiated ping requests are
validated. Ping ACKs now bypass enforcement entirely, enabling
bidirectional keep-alive to work correctly.

Fixes grpc#12417

approved these changes Nov 12, 2025

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