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f5ad399149
The cleanup_srcu_struct_quiesced() function was added because NVME used WQ_MEM_RECLAIM workqueues and SRCU did not, which meant that NVME workqueues waiting on SRCU workqueues could result in deadlocks during low-memory conditions. However, SRCU now also has WQ_MEM_RECLAIM workqueues, so there is no longer a potential for deadlock. Furthermore, it turns out to be extremely hard to use cleanup_srcu_struct_quiesced() correctly due to the fact that SRCU callback invocation accesses the srcu_struct structure's per-CPU data area just after callbacks are invoked. Therefore, the usual practice of using srcu_barrier() to wait for callbacks to be invoked before invoking cleanup_srcu_struct_quiesced() fails because SRCU's callback-invocation workqueue handler might be delayed, which can result in cleanup_srcu_struct_quiesced() being invoked (and thus freeing the per-CPU data) before the SRCU's callback-invocation workqueue handler is finished using that per-CPU data. Nor is this a theoretical problem: KASAN emitted use-after-free warnings because of this problem on actual runs. In short, NVME can now safely invoke cleanup_srcu_struct(), which avoids the use-after-free scenario. And cleanup_srcu_struct_quiesced() is quite difficult to use safely. This commit therefore removes cleanup_srcu_struct_quiesced(), switching its sole user back to cleanup_srcu_struct(). This effectively reverts the following pair of commits: |
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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 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.