a4477988cf
A nice writeup of the LKMM (Linux Kernel Memory Model) rules for access once policies can be found here https://lwn.net/Articles/799218/#Access-Marking%20Policies . The locked and unlocked access to eb::blocking_writers should be annotated accordingly, following this: Writes: - locked write must use ONCE, may use plain read - unlocked write must use ONCE Reads: - unlocked read must use ONCE - locked read may use plain read iff not mixed with unlocked read - unlocked read then locked must use ONCE There's one difference on the assembly level, where btrfs_tree_read_lock_atomic and btrfs_try_tree_read_lock used the cached value and did not reevaluate it after taking the lock. This could have missed some opportunities to take the lock in case blocking writers changed between the calls, but the window is just a few instructions long. As this is in try-lock, the callers handle that. Signed-off-by: David Sterba <dsterba@suse.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 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.