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Documentation: LKMM: Add litmus test for RCU GP guarantee where reader stores

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This adds an example for the important RCU grace period guarantee, which
shows an RCU reader can never span a grace period.

Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2020-03-22 21:57:34 -04:00 committed by Paul E. McKenney
parent be4a37973c
commit a591890c4e
2 changed files with 48 additions and 0 deletions
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11
Documentation/litmus-tests/README Normal file
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============
LITMUS TESTS
============
RCU (/rcu directory)
--------------------
RCU+sync+read.litmus
RCU+sync+free.litmus
Both the above litmus tests demonstrate the RCU grace period guarantee
that an RCU read-side critical section can never span a grace period.

37
Documentation/litmus-tests/rcu/RCU+sync+read.litmus Normal file
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C RCU+sync+read
(*
* Result: Never
*
* This litmus test demonstrates that after a grace period, an RCU updater always
* sees all stores done in prior RCU read-side critical sections. Such
* read-side critical sections would have ended before the grace period ended.
*
* This is one implication of the RCU grace-period guarantee, which says (among
* other things) that an RCU read-side critical section cannot span a grace period.
*)
{
int x = 0;
int y = 0;
}
P0(int *x, int *y)
{
rcu_read_lock();
WRITE_ONCE(*x, 1);
WRITE_ONCE(*y, 1);
rcu_read_unlock();
}
P1(int *x, int *y)
{
int r0;
int r1;
r0 = READ_ONCE(*x);
synchronize_rcu();
r1 = READ_ONCE(*y);
}
exists (1:r0=1 /\ 1:r1=0)