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authorJamie Liu <jamieliu@google.com>2018-10-08 10:19:27 -0700
committerShentubot <shentubot@google.com>2018-10-08 10:20:38 -0700
commite9e8be661328661b5527f1643727b9a13bbeab48 (patch)
treefb6ab9a8e995d56a73b00c237cb6225799f6417c /pkg/linewriter
parent4a00ea557c6e60cdd131b2a9866aa3b0bcb9cb2c (diff)
Implement shared futexes.
- Shared futex objects on shared mappings are represented by Mappable + offset, analogous to Linux's use of inode + offset. Add type futex.Key, and change the futex.Manager bucket API to use futex.Keys instead of addresses. - Extend the futex.Checker interface to be able to return Keys for memory mappings. It returns Keys rather than just mappings because whether the address or the target of the mapping is used in the Key depends on whether the mapping is MAP_SHARED or MAP_PRIVATE; this matters because using mapping target for a futex on a MAP_PRIVATE mapping causes it to stop working across COW-breaking. - futex.Manager.WaitComplete depends on atomic updates to futex.Waiter.addr to determine when it has locked the right bucket, which is much less straightforward for struct futex.Waiter.key. Switch to an atomically-accessed futex.Waiter.bucket pointer. - futex.Manager.Wake now needs to take a futex.Checker to resolve addresses for shared futexes. CLONE_CHILD_CLEARTID requires the exit path to perform a shared futex wakeup (Linux: kernel/fork.c:mm_release() => sys_futex(tsk->clear_child_tid, FUTEX_WAKE, ...)). This is a problem because futexChecker is in the syscalls/linux package. Move it to kernel. PiperOrigin-RevId: 216207039 Change-Id: I708d68e2d1f47e526d9afd95e7fed410c84afccf
Diffstat (limited to 'pkg/linewriter')
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