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Condsider the following call sequence: /* Upper layer */ dma_fence_begin_signalling(); lock(tainted_shared_lock); /* Driver callback */ dma_fence_begin_signalling(); ... The driver might here use a utility that is annotated as intended for the dma-fence signalling critical path. Now if the upper layer isn't correctly annotated yet for whatever reason, resulting in /* Upper layer */ lock(tainted_shared_lock); /* Driver callback */ dma_fence_begin_signalling(); We will receive a false lockdep locking order violation notification from dma_fence_begin_signalling(). However entering a dma-fence signalling critical section itself doesn't block and could not cause a deadlock. So use a successful read_trylock() annotation instead for dma_fence_begin_signalling(). That will make sure that the locking order is correctly registered in the first case, and doesn't register any locking order in the second case. The alternative is of course to make sure that the "Upper layer" is always correctly annotated. But experience shows that's not easily achievable in all cases. Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20230428125233.228353-1-thomas.hellstrom@linux.intel.com |
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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 reStructuredText 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.