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19d39a3810
Moving the irq_request/release_resources() callbacks out of the spinlocked,
irq disabled and bus locked region, unearthed an interesting abuse of the
irq_bus_lock/irq_bus_sync_unlock() callbacks.
The OMAP GPIO driver does merily power management inside of them. The
irq_request_resources() callback of this GPIO irqchip calls a function
which reads a GPIO register. That read aborts now because the clock of the
GPIO block is not magically enabled via the irq_bus_lock() callback.
Move the callbacks under the bus lock again to prevent this. In the
free_irq() path this requires to drop the bus_lock before calling
synchronize_irq() and reaquiring it before calling the
irq_release_resources() callback.
The bus lock can't be held because:
1) The data which has been changed between bus_lock/un_lock is cached in
the irq chip driver private data and needs to go out to the irq chip
via the slow bus (usually SPI or I2C) before calling
synchronize_irq().
That's the reason why this bus_lock/unlock magic exists in the first
place, as you cannot do SPI/I2C transactions while holding desc->lock
with interrupts disabled.
2) synchronize_irq() will actually deadlock, if there is a handler on
flight. These chips use threaded handlers for obvious reasons, as
they allow to do SPI/I2C communication. When the threaded handler
returns then bus_lock needs to be taken in irq_finalize_oneshot() as
we need to talk to the actual irq chip once more. After that the
threaded handler is marked done, which makes synchronize_irq() return.
So if we hold bus_lock accross the synchronize_irq() call, the
handler cannot mark itself done because it blocks on the bus
lock. That in turn makes synchronize_irq() wait forever on the
threaded handler to complete....
Add the missing unlock of desc->request_mutex in the error path of
__free_irq() and add a bunch of comments to explain the locking and
protection rules.
Fixes:
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.. | ||
affinity.c | ||
autoprobe.c | ||
chip.c | ||
cpuhotplug.c | ||
debug.h | ||
debugfs.c | ||
devres.c | ||
dummychip.c | ||
generic-chip.c | ||
handle.c | ||
internals.h | ||
ipi.c | ||
irqdesc.c | ||
irqdomain.c | ||
Kconfig | ||
Makefile | ||
manage.c | ||
migration.c | ||
msi.c | ||
pm.c | ||
proc.c | ||
resend.c | ||
settings.h | ||
spurious.c | ||
timings.c |