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7e7eb5ae4e
Most Linux-kernel uses of locking are straightforward, but there are corner-case uses that rely on less well-known aspects of the lock and unlock primitives. This commit therefore adds a locking.txt and litmus tests in Documentation/litmus-tests/locking to explain these corner-case uses. [ paulmck: Apply Andrea Parri feedback for klitmus7. ] [ paulmck: Apply Akira Yokosawa example-consistency feedback. ] Reviewed-by: Akira Yokosawa <akiyks@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
54 lines
811 B
Text
54 lines
811 B
Text
C DCL-broken
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(*
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* Result: Sometimes
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*
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* This litmus test demonstrates more than just locking is required to
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* correctly implement double-checked locking.
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*)
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{
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int flag;
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int data;
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}
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P0(int *flag, int *data, spinlock_t *lck)
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{
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int r0;
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int r1;
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int r2;
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r0 = READ_ONCE(*flag);
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if (r0 == 0) {
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spin_lock(lck);
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r1 = READ_ONCE(*flag);
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if (r1 == 0) {
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WRITE_ONCE(*data, 1);
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WRITE_ONCE(*flag, 1);
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}
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spin_unlock(lck);
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}
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r2 = READ_ONCE(*data);
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}
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P1(int *flag, int *data, spinlock_t *lck)
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{
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int r0;
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int r1;
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int r2;
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r0 = READ_ONCE(*flag);
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if (r0 == 0) {
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spin_lock(lck);
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r1 = READ_ONCE(*flag);
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if (r1 == 0) {
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WRITE_ONCE(*data, 1);
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WRITE_ONCE(*flag, 1);
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}
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spin_unlock(lck);
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}
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r2 = READ_ONCE(*data);
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}
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locations [flag;data;0:r0;0:r1;1:r0;1:r1]
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exists (0:r2=0 \/ 1:r2=0)
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