bgpd: fix premature deletion of already-stale routes during GR clearing

[miteshkanjariya]

When a peer goes down with GR enabled, routes already marked
BGP_PATH_STALE were incorrectly deleted instead of being preserved
for the current GR cycle. Remove the BGP_PATH_STALE check from both
bgp_clear_route_node() and clearing_clear_one_pi() so that stale
routes are re-marked rather than removed. Stale route cleanup remains
handled by bgp_clear_stale_route() on timer expiry.

Signed-off-by: Mitesh Kanjariyamkanjariya@nvidia.com

[greptile-apps]

Greptile Overview

Greptile Summary

Fixed premature deletion of already-stale BGP routes during Graceful Restart (GR) clearing by removing BGP_PATH_STALE checks from bgp_clear_route_node() and clearing_clear_one_pi().

Key changes:

• Routes already marked BGP_PATH_STALE (from prior enhanced refresh or GR cycles) are now re-marked stale instead of being deleted during a new GR cycle
• Stale route cleanup remains properly handled by bgp_clear_stale_route() on timer expiry
• Added comprehensive test case that triggers enhanced-refresh (BoRR) to mark routes stale, then kills bgpd to verify already-stale routes are preserved during GR
• Test configurations added for routers r5 and r6 with GR enabled

Impact:
This fix ensures correct behavior when a peer goes down with GR enabled - routes that were already stale are preserved for the current GR cycle rather than being prematurely removed.

Confidence Score: 5/5

• This PR is safe to merge - it fixes a clear bug in GR handling with minimal, well-understood changes
• The fix is surgical and correct: removing the BGP_PATH_STALE check allows already-stale routes to be re-marked rather than deleted during GR cycles. The logic is sound - stale route cleanup is properly delegated to bgp_clear_stale_route() on timer expiry. Comprehensive test coverage validates the fix.
• No files require special attention - all changes are straightforward and well-tested

Important Files Changed

Filename	Overview
bgpd/bgp_route.c	Removes BGP_PATH_STALE check from two functions to prevent premature deletion of already-stale routes during GR cycles
tests/topotests/bgp_gr_restart_retain_routes/test_bgp_gr_preserve_already_stale_routes.py	Adds test case that triggers enhanced-refresh to mark routes stale, then kills bgpd to verify already-stale routes are preserved during GR

[greptile-apps]

_{2 files reviewed, 1 comment}

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[miteshkanjariya]

ci:rerun

[miteshkanjariya]

ci:rerun

[ton31337]

Is this broken after c527882?

[miteshkanjariya]

Is this broken after c527882?

yes, this surfaced as a result of the batch clearing fix. I had created another MR in that code path: #20738.

But this fix should be made regardless of that issue, as we are deleting a route in the GR code flow if it was previously marked stale.

[ton31337]

@Mergifyio backport dev/10.6 stable/10.5 stable/10.4

[mergify]

backport dev/10.6 stable/10.5 stable/10.4

✅ Backports have been created

Details

• #20801 bgpd: fix premature deletion of already-stale routes during GR clearing (backport #20768) has been created for branch dev/10.6
• #20802 bgpd: fix premature deletion of already-stale routes during GR clearing (backport #20768) has been created for branch stable/10.5 but encountered conflicts

Cherry-pick of 968ccc4 has failed:

On branch mergify/bp/stable/10.5/pr-20768
Your branch is ahead of 'origin/stable/10.5' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 968ccc471.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   bgpd/bgp_route.c

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

• #20803 bgpd: fix premature deletion of already-stale routes during GR clearing (backport #20768) has been created for branch stable/10.4 but encountered conflicts

Cherry-pick of 968ccc4 has failed:

On branch mergify/bp/stable/10.4/pr-20768
Your branch is ahead of 'origin/stable/10.4' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 968ccc471.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   bgpd/bgp_route.c

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally