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Function gfs2_clear_rgrpd() is called during unmount to free all rgrps and their sub-objects. If the rgrp glock is held (e.g. in SH) it calls gfs2_glock_cb() to unlock, then calls flush_delayed_work() to make sure any glock work is finished. However, there is a race with other cluster nodes who may request the rgrp glock in another mode (say, EX). Func gfs2_clear_rgrpd() calls glock_clear_object() which sets gl_object to NULL but that's done without holding the gl_lockref spin_lock. While the lock is not held Another node's demote request can cause the state machine to run again, and since the gl_lockref is released in do_xmote, the second process's call to do_xmote can call go_inval (rgrp_go_inval) after the gl_object has been cleared, which results in NULL pointer reference of the rgrp glock's gl_object. Other go_inval glops functions don't require the gl_object to exist, as evidenced by function inode_go_inval() which explicitly checks for if (ip) before referencing gl_object. This patch does the same thing for rgrp glocks. Both the go_inval and go_sync ops are patched to check the existence of gl_object (rgd) before trying to dereference it. Signed-off-by: Bob Peterson <rpeterso@redhat.com> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.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.