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Subject: three locks and lock order reversal?
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Hi,

The test code below will result witness's warning of "lock order
reversal":

/* lock A then B */
mtx_lock(&A_mtx);
mtx_lock(&B_mtx); 
mtx_unlock(&B_mtx);
mtx_unlock(&A_mtx);

/* lock B then C */
mtx_lock(&B_mtx);
mtx_lock(&C_mtx);
mtx_unlock(&C_mtx);
mtx_unlock(&B_mtx);

/* lock C then A, witness will complaint! */
mtx_lock(&C_mtx);
mtx_lock(&A_mtx);
mtx_unlock(&A_mtx);
mtx_unlock(&C_mtx);

But the code seems healthy and will not cause dead locking. So I guess
that the lock order relationship should not be transferrable. Or am I
missing something?

song

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