Bug 2468074 (CVE-2026-43326)

Summary: CVE-2026-43326 kernel: sched_ext: Fix SCX_KICK_WAIT deadlock by deferring wait to balance callback
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel, specifically within the `sched_ext` component. This vulnerability can lead to a system-wide deadlock, causing a Denial of Service (DoS) where the system becomes unresponsive. The issue arises when the kernel's scheduling mechanism enters a busy-wait state in a critical section, preventing processors from performing other tasks. If multiple processors become stuck in this waiting loop, the entire system can freeze.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-05-08 14:03:08 UTC 
In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Fix SCX_KICK_WAIT deadlock by deferring wait to balance callback

SCX_KICK_WAIT busy-waits in kick_cpus_irq_workfn() using
smp_cond_load_acquire() until the target CPU's kick_sync advances. Because
the irq_work runs in hardirq context, the waiting CPU cannot reschedule and
its own kick_sync never advances. If multiple CPUs form a wait cycle, all
CPUs deadlock.

Replace the busy-wait in kick_cpus_irq_workfn() with resched_curr() to
force the CPU through do_pick_task_scx(), which queues a balance callback
to perform the wait. The balance callback drops the rq lock and enables
IRQs following the sched_core_balance() pattern, so the CPU can process
IPIs while waiting. The local CPU's kick_sync is advanced on entry to
do_pick_task_scx() and continuously during the wait, ensuring any CPU that
starts waiting for us sees the advancement and cannot form cyclic
dependencies.
Comment 1 Alexander B 2026-05-15 11:29:41 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-43326.mbox