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 e04268b0ef ("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 9114014cf4 ("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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