Backport(v1.19): Fix out_forward keepalive reuse after remote close (#5309) - #5343
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**Which issue(s) this PR fixes**: Fixes #5269 Fixes #4618 **What this PR does / why we need it**: This PR fixes a keepalive socket reuse bug in `out_forward`. When a cached keepalive connection has already been closed by the remote side, `out_forward` could pick that socket back up and try to write to it again. In the reported TLS/NLB setup, that leaves the flush thread spinning on a dead socket and can drive CPU usage to 100%. The fix is to validate cached sockets before reusing them. If a socket has already become unreadable, closed, or otherwise looks no longer safe to reuse, it is discarded and a new connection is created instead. This keeps `out_forward` from reusing half-closed keepalive sockets and avoids the busy-loop behavior described in the issue. This PR also adds regression coverage to make sure a socket that was closed by the peer is not reused from the keepalive cache. **Docs Changes**: None. **Release Note**: - out_forward: avoid reusing closed keepalive sockets after remote disconnects Signed-off-by: aviralgarg05 <gargaviral99@gmail.com> Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Watson1978
approved these changes
Apr 20, 2026
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Which issue(s) this PR fixes:
Fixes #5269
Fixes #4618
What this PR does / why we need it:
This PR fixes a keepalive socket reuse bug in
out_forward.When a cached keepalive connection has already been closed by the remote side,
out_forwardcould pick that socket back up and try to write to it again. In the reported TLS/NLB setup, that leaves the flush thread spinning on a dead socket and can drive CPU usage to 100%.The fix is to validate cached sockets before reusing them. If a socket has already become unreadable, closed, or otherwise looks no longer safe to reuse, it is discarded and a new connection is created instead.
This keeps
out_forwardfrom reusing half-closed keepalive sockets and avoids the busy-loop behavior described in the issue.This PR also adds regression coverage to make sure a socket that was closed by the peer is not reused from the keepalive cache.
Docs Changes:
None.
Release Note: