mainlining shenanigans
c83ff01864
Currently we blow up in trace_dma_fence_init, when calling into get_driver_name or get_timeline_name, since both the engine and context might be NULL(or contain some garbage address) in the case of newly allocated slab objects via the request ctor. Note that we also use SLAB_TYPESAFE_BY_RCU here, which allows requests to be immediately freed, but delay freeing the underlying page by an RCU grace period. With this scheme requests can be re-allocated, at the same time as they are also being read by some lockless RCU lookup mechanism. In the ctor case, which is only called for new slab objects(i.e allocate new page and call the ctor for each object) it's safe to reset the context/engine prior to calling into dma_fence_init, since we can be certain that no one is doing an RCU lookup which might depend on peeking at the engine/context, like in active_engine(), since the object can't yet be externally visible. In the recycled case(which might also be externally visible) the request refcount always transitions from 0->1 after we set the context/engine etc, which should ensure it's valid to dereference the engine for example, when doing an RCU list-walk, so long as we can also increment the refcount first. If the refcount is already zero, then the request is considered complete/released. If it's non-zero, then the request might be in the process of being re-allocated, or potentially still in flight, however after successfully incrementing the refcount, it's possible to carefully inspect the request state, to determine if the request is still what we were looking for. Note that all externally visible requests returned to the cache must have zero refcount. One possible fix then is to move dma_fence_init out from the request ctor. Originally this was how it was done, but it was moved in: commit |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
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| mm | ||
| net | ||
| samples | ||
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| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
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| .gitignore | ||
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.