e90402fb06
[ Upstream commit 05eda6e75773592760285e10ac86c56d683be17f ]
It is possible for free_blocked_lock() to be called twice concurrently,
once from nfsd4_lock() and once from nfsd4_release_lockowner() calling
remove_blocked_locks(). This is why a kref was added.
It is perfectly safe for locks_delete_block() and kref_put() to be
called in parallel as they use locking or atomicity respectively as
protection. However locks_release_private() has no locking. It is
safe for it to be called twice sequentially, but not concurrently.
This patch moves that call from free_blocked_lock() where it could race
with itself, to free_nbl() where it cannot. This will slightly delay
the freeing of private info or release of the owner - but not by much.
It is arguably more natural for this freeing to happen in free_nbl()
where the structure itself is freed.
This bug was found by code inspection - it has not been seen in practice.
Fixes: 47446d74f170 ("nfsd4: add refcount for nfsd4_blocked_lock")
Signed-off-by: NeilBrown <neilb@suse.de>
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 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.