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The nfsd4_callback workqueue jobs exist to queue backchannel RPCs to rpciod. Because they run in different workqueue contexts, the rpc_task can run concurrently with the workqueue job itself, should it become requeued. This is problematic as there is no locking when accessing the fields in the nfsd4_callback. Add a new unsigned long to nfsd4_callback and declare a new NFSD4_CALLBACK_RUNNING flag to be set in it. When attempting to run a workqueue job, do a test_and_set_bit() on that flag first, and don't queue the workqueue job if it returns true. Clear NFSD4_CALLBACK_RUNNING in nfsd41_destroy_cb(). This also gives us a more reliable mechanism for handling queueing failures in codepaths where we have to take references under spinlocks. We can now do the test_and_set_bit on NFSD4_CALLBACK_RUNNING first, and only take references to the objects if that returns false. Most of the nfsd4_run_cb() callers are converted to use this new flag or the nfsd4_try_run_cb() wrapper. The main exception is the callback channel probe, which has its own synchronization. Signed-off-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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.