From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 13 Dec 2015 17:12:30 +0000 (+0100)
Subject: genirq: Prevent chip buslock deadlock
X-Git-Tag: v3.2.76~31
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=18020036abfe56b51b08f2e337482ce8b2237eea;p=pandora-kernel.git

genirq: Prevent chip buslock deadlock

commit abc7e40c81d113ef4bacb556f0a77ca63ac81d85 upstream.

If a interrupt chip utilizes chip->buslock then free_irq() can
deadlock in the following way:

CPU0				CPU1
				interrupt(X) (Shared or spurious)
free_irq(X)			interrupt_thread(X)
chip_bus_lock(X)
				   irq_finalize_oneshot(X)
				     chip_bus_lock(X)
synchronize_irq(X)

synchronize_irq() waits for the interrupt thread to complete,
i.e. forever.

Solution is simple: Drop chip_bus_lock() before calling
synchronize_irq() as we do with the irq_desc lock. There is nothing to
be protected after the point where irq_desc lock has been released.

This adds chip_bus_lock/unlock() to the remove_irq() code path, but
that's actually correct in the case where remove_irq() is called on
such an interrupt. The current users of remove_irq() are not affected
as none of those interrupts is on a chip which requires buslock.

Reported-by: Fredrik Markström <fredrik.markstrom@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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