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authorLukas Wunner <lukas@wunner.de>2018-06-24 10:35:18 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-06-24 14:17:26 +0200
commit836557bd58e5e65c05c73af9f6ebed885dbfccfc (patch)
tree04dd91fa220751c9b013fad06eb4cd38432f5ea0
parent74bdf7815dfb3805a37b0bba615814063a227bf5 (diff)
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 commit e04268b0effc ("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 commit 9114014cf4e6 ("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
-rw-r--r--kernel/irq/manage.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 591cfe901162..123a227d3357 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1025,10 +1025,7 @@ static int irq_thread(void *data)
* This is the regular exit path. __free_irq() is stopping the
* thread via kthread_stop() after calling
* synchronize_irq(). So neither IRQTF_RUNTHREAD nor the
- * oneshot mask bit can be set. We cannot verify that as we
- * cannot touch the oneshot mask at this point anymore as
- * __setup_irq() might have given out currents thread_mask
- * again.
+ * oneshot mask bit can be set.
*/
task_work_cancel(current, irq_thread_dtor);
return 0;
@@ -1245,7 +1242,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
/*
* Protects against a concurrent __free_irq() call which might wait
* for synchronize_irq() to complete without holding the optional
- * chip bus lock and desc->lock.
+ * chip bus lock and desc->lock. Also protects against handing out
+ * a recycled oneshot thread_mask bit while it's still in use by
+ * its previous owner.
*/
mutex_lock(&desc->request_mutex);