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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2020-05-26 16:41:34 +0300
committerPaul E. McKenney <paulmck@kernel.org>2020-06-29 22:01:22 +0300
commitbde50d8ff83e4ce9e576f7c5ba1edb48a3610a5b (patch)
tree32485e0cd75b9ab64871cb222a11ea404b7e6354 /Documentation/admin-guide
parent7fef6cff8f2814bf8eb632e2bb8f0a987ffd9ece (diff)
downloadlinux-bde50d8ff83e4ce9e576f7c5ba1edb48a3610a5b.tar.xz
srcu: Avoid local_irq_save() before acquiring spinlock_t
SRCU disables interrupts to get a stable per-CPU pointer and then acquires the spinlock which is in the per-CPU data structure. The release uses spin_unlock_irqrestore(). While this is correct on a non-RT kernel, this conflicts with the RT semantics because the spinlock is converted to a 'sleeping' spinlock. Sleeping locks can obviously not be acquired with interrupts disabled. Acquire the per-CPU pointer `ssp->sda' without disabling preemption and then acquire the spinlock_t of the per-CPU data structure. The lock will ensure that the data is consistent. The added call to check_init_srcu_struct() is now needed because a statically defined srcu_struct may remain uninitialized until this point and the newly introduced locking operation requires an initialized spinlock_t. This change was tested for four hours with 8*SRCU-N and 8*SRCU-P without causing any warnings. Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: rcu@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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