On Thu, Sep 11, 2025 at 01:35:33PM -0700, Tahera Fahimi wrote:

Dear Stable Kernel Maintainers,

I am writing to request the backport of the following patches to stable kernel versions 6.6.y, addressing a deadlock issue in RCU Tasks related to do_exit() on preemptible systems.

Issue Description: The kernel may experience deadlocks due to shared locking between exit_tasks_rcu_start() and rcu_tasks_postscan() via synchronize_srcu(), when multiple processes exit concurrently. The problem manifests as stalls in the RCU tasks grace period. This issue manifest as a deadlock in WSL kernel which uses the stable kernel 6.6.87 (Please see the issue on https://github.com/microsoft/WSL/issues/13480)

Patches to Apply: Patch 1: Subject: rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks Commit ID: 6b70399f9ef3809f6e308fd99dd78b072c1bd05c Justification: Introduces per-CPU lists for exiting tasks, replacing SRCU-based waits and eliminating deadlocks during concurrent exits. Patch 2: Subject: rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks Commit ID: 1612160b91272f5b1596f499584d6064bf5be794 Justification: Ensures all exiting tasks are properly gathered and synchronized, preventing missed synchronizations and further deadlocks. Patch 3: Subject: rcu-tasks: Maintain real-time response in rcu_tasks_postscan() Commit ID: 0bb11a372fc8d7006b4d0f42a2882939747bdbff Justification: Periodically enables interrupts during per-CPU list traversal to maintain system responsiveness, especially when many tasks are present.

Kernel version: latest kernel version in 6.6.y branch

Now queued up, thanks.

greg k-h