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- This guide is an attempt to make explicit the locking assumptions
- made by the InfiniBand midlayer. It describes the requirements on
- both low-level drivers that sit below the midlayer and upper level
- protocols that use the midlayer.
-Sleeping and interrupt context
- With the following exceptions, a low-level driver implementation of
- all of the methods in struct ib_device may sleep. The exceptions
- are any methods from the list:
- create_ah
- modify_ah
- query_ah
- destroy_ah
- bind_mw
- post_send
- post_recv
- poll_cq
- req_notify_cq
- map_phys_fmr
- which may not sleep and must be callable from any context.
- The corresponding functions exported to upper level protocol
- consumers:
- ib_create_ah
- ib_modify_ah
- ib_query_ah
- ib_destroy_ah
- ib_bind_mw
- ib_post_send
- ib_post_recv
- ib_req_notify_cq
- ib_map_phys_fmr
- are therefore safe to call from any context.
- In addition, the function
- ib_dispatch_event
- used by low-level drivers to dispatch asynchronous events through
- the midlayer is also safe to call from any context.
- All of the methods in struct ib_device exported by a low-level
- driver must be fully reentrant. The low-level driver is required to
- perform all synchronization necessary to maintain consistency, even
- if multiple function calls using the same object are run
- simultaneously.
- The IB midlayer does not perform any serialization of function calls.
- Because low-level drivers are reentrant, upper level protocol
- consumers are not required to perform any serialization. However,
- some serialization may be required to get sensible results. For
- example, a consumer may safely call ib_poll_cq() on multiple CPUs
- simultaneously. However, the ordering of the work completion
- information between different calls of ib_poll_cq() is not defined.
- A low-level driver must not perform a callback directly from the
- same callchain as an ib_device method call. For example, it is not
- allowed for a low-level driver to call a consumer's completion event
- handler directly from its post_send method. Instead, the low-level
- driver should defer this callback by, for example, scheduling a
- tasklet to perform the callback.
- The low-level driver is responsible for ensuring that multiple
- completion event handlers for the same CQ are not called
- simultaneously. The driver must guarantee that only one CQ event
- handler for a given CQ is running at a time. In other words, the
- following situation is not allowed:
- low-level driver ->
- consumer CQ event callback:
- /* ... */
- ib_req_notify_cq(cq, ...);
- low-level driver ->
- /* ... */ consumer CQ event callback:
- /* ... */
- return from CQ event handler
- The context in which completion event and asynchronous event
- callbacks run is not defined. Depending on the low-level driver, it
- may be process context, softirq context, or interrupt context.
- Upper level protocol consumers may not sleep in a callback.
- A low-level driver announces that a device is ready for use by
- consumers when it calls ib_register_device(), all initialization
- must be complete before this call. The device must remain usable
- until the driver's call to ib_unregister_device() has returned.
- A low-level driver must call ib_register_device() and
- ib_unregister_device() from process context. It must not hold any
- semaphores that could cause deadlock if a consumer calls back into
- the driver across these calls.
- An upper level protocol consumer may begin using an IB device as
- soon as the add method of its struct ib_client is called for that
- device. A consumer must finish all cleanup and free all resources
- relating to a device before returning from the remove method.
- A consumer is permitted to sleep in its add and remove methods.