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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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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.