path: root/arch/hexagon/Kconfig
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authorFrederic Weisbecker <fweisbec@gmail.com>2012-10-30 13:33:54 +0100
committerFrederic Weisbecker <fweisbec@gmail.com>2012-11-14 17:36:05 +0100
commitc8446b75be6f85b3d40066922876cb7adc948afb (patch)
tree8fa5f2671166c976795ecad46e63ead43669f909 /arch/hexagon/Kconfig
parent3d70f8c617a436c7146ecb81df2265b4626dfe89 (diff)
irq_work: Fix racy IRQ_WORK_BUSY flag setting
The IRQ_WORK_BUSY flag is set right before we execute the work. Once this flag value is set, the work enters a claimable state again. So if we have specific data to compute in our work, we ensure it's either handled by another CPU or locally by enqueuing the work again. This state machine is guanranteed by atomic operations on the flags. So when we set IRQ_WORK_BUSY without using an xchg-like operation, we break this guarantee as in the following summarized scenario: CPU 1 CPU 2 ----- ----- (flags = 0) old_flags = flags; (flags = 0) cmpxchg(flags, old_flags, old_flags | IRQ_WORK_FLAGS) (flags = 3) [...] flags = IRQ_WORK_BUSY (flags = 2) func() (sees flags = 3) cmpxchg(flags, old_flags, old_flags | IRQ_WORK_FLAGS) (give up) cmpxchg(flags, 2, 0); (flags = 0) CPU 1 claims a work and executes it, so it sets IRQ_WORK_BUSY and the work is again in a claimable state. Now CPU 2 has new data to process and try to claim that work but it may see a stale value of the flags and think the work is still pending somewhere that will handle our data. This is because CPU 1 doesn't set IRQ_WORK_BUSY atomically. As a result, the data expected to be handle by CPU 2 won't get handled. To fix this, use xchg() to set IRQ_WORK_BUSY, this way we ensure the CPU 2 will see the correct value with cmpxchg() using the expected ordering. Changelog-heavily-inspired-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Anish Kumar <anish198519851985@gmail.com>
Diffstat (limited to 'arch/hexagon/Kconfig')
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