Commit 9ea2b810 authored by Muchun Song's avatar Muchun Song Committed by Thomas Gleixner
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genirq/proc: Fix race in show_irq_affinity() 



Reading /proc/irq/N/smp_affinity* races with irq_set_affinity() and
irq_move_masked_irq(), leading to old or torn output for users.

After a user writes a new CPU mask to /proc/irq/N/affinity*, the syscall
returns success, yet a subsequent read of the same file immediately returns
a value different from what was just written.

That's due to a race between show_irq_affinity() and irq_move_masked_irq()
which lets the read observe a transient, inconsistent affinity mask.

Cure it by guarding the read with irq_desc::lock.

[ tglx: Massaged change log ]

Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251028090408.76331-1-songmuchun@bytedance.com
parent 68c4c159

kernel/irq/proc.c

+2 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ static int show_irq_affinity(int type, struct seq_file *m) 
	struct irq_desc *desc = irq_to_desc((long)m->private);

	const struct cpumask *mask;



	guard(raw_spinlock_irq)(&desc->lock);



	switch (type) {

	case AFFINITY:

	case AFFINITY_LIST: