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Fix a bug where dynamic CPU isolation through cpuset isolated partitions

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can move a kthread out of the housekeeping range. For example in a
 system with 3 CPUs:
 
 _ kthread K has preferred affinity to CPUs 1 et 2 and is affine to them
 _ CPU 1 goes offline
 _ An isolated cpuset partition is created on CPU 2 (so the only
   remaining online housekeeper is CPU 0)
 _ K is affine to CPU 2 but this CPU is offline so it fails and goes back
   to its previous affinity where only CPU 3 is online. Yet it is
   isolated.
 
 The fix makes sure the fallback affinity is always a set of online
 housekeeper.
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Merge tag 'kthread-fix-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks

Pull kthread fix from Frederic Weisbecker:
 "Fix a bug where dynamic CPU isolation through cpuset isolated
  partitions can move a kthread out of the housekeeping range.

  The fix makes sure the fallback affinity is always a set of online
  housekeeper"

* tag 'kthread-fix-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks:
  kthread: Fall back when no preferred housekeeping CPU is online
This commit is contained in:
Linus Torvalds 2026-10-29 07:49:07 -10:00
commit d011f648a7
1 changed files with 1 additions and 1 deletions
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2
kernel/kthread.c
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@ -343,7 +343,7 @@ static void kthread_fetch_affinity(struct kthread *kthread, struct cpumask *cpum
}
cpumask_and(cpumask, pref, housekeeping_cpumask(HK_TYPE_DOMAIN));
if (cpumask_empty(cpumask))
if (!cpumask_intersects(cpumask, cpu_online_mask))
cpumask_copy(cpumask, housekeeping_cpumask(HK_TYPE_DOMAIN));
}