80793c3471
Latch sequence counters are a multiversion concurrency control mechanism where the seqcount_t counter even/odd value is used to switch between two copies of protected data. This allows the seqcount_t read path to safely interrupt its write side critical section (e.g. from NMIs). Initially, latch sequence counters were implemented as a single write function above plain seqcount_t: raw_write_seqcount_latch(). The read side was expected to use plain seqcount_t raw_read_seqcount(). A specialized latch read function, raw_read_seqcount_latch(), was later added. It became the standardized way for latch read paths. Due to the dependent load, it has one read memory barrier less than the plain seqcount_t raw_read_seqcount() API. Only raw_write_seqcount_latch() and raw_read_seqcount_latch() should be used with latch sequence counters. Having *unique* read and write path APIs means that latch sequence counters are actually a data type of their own -- just inappropriately overloading plain seqcount_t. Introduce seqcount_latch_t. This adds type-safety and ensures that only the correct latch-safe APIs are to be used. Not to break bisection, let the latch APIs also accept plain seqcount_t or seqcount_raw_spinlock_t. After converting all call sites to seqcount_latch_t, only that new data type will be allowed. References: |
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| README | ||
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.