CVE-2026-68438smp: Make CSD lock acquisition atomic for debug mode

In the Linux kernel, the following vulnerability has been resolved: smp: Make CSD lock acquisition atomic for debug mode Commit b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") changed smp_call_function_single() so that, when CSD lock debugging is enabled, async !wait calls use the destination CPU csd_data. That improves diagnostics, but it also removes the single-writer property that made the old csd_lock() safe: multiple CPUs can now prepare the same destination CPU CSD concurrently. csd_lock() currently waits for CSD_FLAG_LOCK to clear and then sets the bit with a non-atomic read-modify-write. Two senders can both see an unlocked CSD, set the bit, overwrite the callback fields, and enqueue the same llist node. Re-adding a node that is already the queue head can make node->next point to itself, leaving the target CPU stuck walking call_single_queue. Later synchronous work, such as a TLB shootdown, can then remain queued and trigger soft-lockup warnings or panics. Keep the single csd_lock() implementation, but when CSD lock debugging is enabled, acquire CSD_FLAG_LOCK with try_cmpxchg_acquire(). This makes the destination CPU CSD a real atomic lock in the only configuration where it can be shared by multiple remote senders, while preserving the existing non-debug fast path.

CVSS

Not yet scored

Weakness (CWE)

Not given

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

Linux

NVD analysis

Received

Record last updated

Aug 17, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

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