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/linux-master/include/linux/
H A Dsrcu.hdiff 3bc97a78 Thu Nov 29 01:46:05 MST 2012 Lai Jiangshan <laijs@cn.fujitsu.com> srcu: Remove checks preventing offline CPUs from calling srcu_read_lock()

SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of c0d6d01b (rcu: Check for illegal use of RCU from offlined CPUs).

It also makes the code match the comments in whatisRCU.txt:

g. Do you need read-side critical sections that are respected
even though they are in the middle of the idle loop, during
user-mode execution, or on an offlined CPU? If so, SRCU is the
only choice that will work for you.

[ paulmck: There is at least one remaining issue, namely use of lockdep
with tracing enabled. ]

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff c0d6d01b Mon Jan 23 01:41:26 MST 2012 Paul E. McKenney <paulmck@kernel.org> rcu: Check for illegal use of RCU from offlined CPUs

Although it is legal to use RCU during early boot, it is anything
but legal to use RCU at runtime from an offlined CPU. After all, RCU
explicitly ignores offlined CPUs. This commit therefore adds checks
for runtime use of RCU from offlined CPUs.

These checks are not perfect, in particular, they can be subverted
through use of things like rcu_dereference_raw(). Note that it is not
possible to put checks in rcu_read_lock() and friends due to the fact
that these primitives are used in code that might be used under either
RCU or lock-based protection, which means that checking rcu_read_lock()
gets you fat piles of false positives.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
H A Drcupdate.hdiff c0d6d01b Mon Jan 23 01:41:26 MST 2012 Paul E. McKenney <paulmck@kernel.org> rcu: Check for illegal use of RCU from offlined CPUs

Although it is legal to use RCU during early boot, it is anything
but legal to use RCU at runtime from an offlined CPU. After all, RCU
explicitly ignores offlined CPUs. This commit therefore adds checks
for runtime use of RCU from offlined CPUs.

These checks are not perfect, in particular, they can be subverted
through use of things like rcu_dereference_raw(). Note that it is not
possible to put checks in rcu_read_lock() and friends due to the fact
that these primitives are used in code that might be used under either
RCU or lock-based protection, which means that checking rcu_read_lock()
gets you fat piles of false positives.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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