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Perhaps the biggest potential problem, though, is that the memory model implemented by C11 atomics does not exactly match the model used by the kernel. The C11 model is based on acquire/release semantics — one-way barriers that are described in the 2014 article and this article. Much of the kernel, instead, makes use of load/store barriers, which are stricter, two-way barriers. A memory write with release semantics will only complete after any previous reads or writes are visible throughout the system, but it allows other operations made logically after the write to be reordered to happen before that write. A write with store semantics, instead, strictly orders other write operations on both sides of the barrier.

As Will Deacon pointed out, C11 atomics lack a good implementation of consume load operations, which are an important part of read-copy-update (RCU), among other things. A consume load can always be replaced with an acquire operation, but the performance will be worse. In general, Will worries that the C11 model is a poor fit for the ARM architecture, and that the result of a switch might be an unwieldy combination of C11 and kernel-specific operations. He did agree, though, that a generic implementation based on C11 atomics would be a useful tool for developers bringing up the kernel on a new architecture.

Perhaps the biggest potential problem, though, is that the memory model implemented by C11 atomics does not exactly match the model used by the kernel. The C11 model is based on acquire/release semantics — one-way barriers that are described in the 2014 article and this article. Much of the kernel, instead, makes use of load/store barriers, which are stricter, two-way barriers. A memory write with release semantics will only complete after any previous reads or writes are visible throughout the system, but it allows other operations made logically after the write to be reordered to happen before that write. A write with store semantics, instead, strictly orders other write operations on both sides of the barrier.