79262bf1f0
Old implemention used Giant to protect the kernel data structures, but at the same time called malloc(M_WAITOK), that could cause the calling thread to sleep and lost Giant protection. User-visible result was the missed wakeup. New implementation uses one sx lock per futex. The sx protects the futex structures and allows to sleep while copyin or copyout are performed. Unlike linux, we return EINVAL when FUTEX_CMP_REQUEUE operation is requested and either caller specified futexes are equial or second futex already exists. This is acceptable since the situation can only occur from the application error, and glibc falls back to old FUTEX_WAKE operation when FUTEX_CMP_REQUEUE returns an error. Approved by: kib (mentor) MFC after: 1 month |
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