forked from luck/tmp_suning_uos_patched
genirq: Update code comments wrt recycled thread_mask
Previously a race existed between __free_irq() and __setup_irq() wherein the thread_mask of a just removed action could be handed out to a newly added action and the freed irq thread would then tread on the oneshot mask bit of the newly added irq thread in irq_finalize_oneshot(): time | __free_irq() | raw_spin_lock_irqsave(&desc->lock, flags); | <remove action from linked list> | raw_spin_unlock_irqrestore(&desc->lock, flags); | | __setup_irq() | raw_spin_lock_irqsave(&desc->lock, flags); | <traverse linked list to determine oneshot mask bit> | raw_spin_unlock_irqrestore(&desc->lock, flags); | | irq_thread() of freed irq (__free_irq() waits in synchronize_irq()) | irq_thread_fn() | irq_finalize_oneshot() | raw_spin_lock_irq(&desc->lock); | desc->threads_oneshot &= ~action->thread_mask; | raw_spin_unlock_irq(&desc->lock); v The race was known at least since 2012 when it was documented in a code comment by commite04268b0ef
("genirq: Remove paranoid warnons and bogus fixups"). The race itself is harmless as nothing touches any of the potentially freed data after synchronize_irq(). In 2017 the race was close by commit9114014cf4
("genirq: Add mutex to irq desc to serialize request/free_irq()"), apparently inadvertantly so because the race is neither mentioned in the commit message nor was the code comment updated. Make up for that. Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Mika Westerberg <mika.westerberg@linux.intel.com> Cc: linux-pci@vger.kernel.org Link: https://lkml.kernel.org/r/32fc25aa35ecef4b2692f57687bb7fc2a57230e2.1529828292.git.lukas@wunner.de
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@ -1025,10 +1025,7 @@ static int irq_thread(void *data)
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* This is the regular exit path. __free_irq() is stopping the
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* thread via kthread_stop() after calling
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* synchronize_irq(). So neither IRQTF_RUNTHREAD nor the
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* oneshot mask bit can be set. We cannot verify that as we
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* cannot touch the oneshot mask at this point anymore as
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* __setup_irq() might have given out currents thread_mask
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* again.
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* oneshot mask bit can be set.
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*/
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task_work_cancel(current, irq_thread_dtor);
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return 0;
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@ -1245,7 +1242,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
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/*
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* Protects against a concurrent __free_irq() call which might wait
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* for synchronize_irq() to complete without holding the optional
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* chip bus lock and desc->lock.
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* chip bus lock and desc->lock. Also protects against handing out
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* a recycled oneshot thread_mask bit while it's still in use by
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* its previous owner.
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*/
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mutex_lock(&desc->request_mutex);
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