diff --git a/Documentation/filesystems/xfs-online-fsck-design.rst b/Documentation/filesystems/xfs-online-fsck-design.rst
index a03a7b9f0250..d630b6bdbe4a 100644
--- a/Documentation/filesystems/xfs-online-fsck-design.rst
+++ b/Documentation/filesystems/xfs-online-fsck-design.rst
@@ -563,3 +563,190 @@ functionality.
 Many of these risks are inherent to software programming.
 Despite this, it is hoped that this new functionality will prove useful in
 reducing unexpected downtime.
+
+3. Testing Plan
+===============
+
+As stated before, fsck tools have three main goals:
+
+1. Detect inconsistencies in the metadata;
+
+2. Eliminate those inconsistencies; and
+
+3. Minimize further loss of data.
+
+Demonstrations of correct operation are necessary to build users' confidence
+that the software behaves within expectations.
+Unfortunately, it was not really feasible to perform regular exhaustive testing
+of every aspect of a fsck tool until the introduction of low-cost virtual
+machines with high-IOPS storage.
+With ample hardware availability in mind, the testing strategy for the online
+fsck project involves differential analysis against the existing fsck tools and
+systematic testing of every attribute of every type of metadata object.
+Testing can be split into four major categories, as discussed below.
+
+Integrated Testing with fstests
+-------------------------------
+
+The primary goal of any free software QA effort is to make testing as
+inexpensive and widespread as possible to maximize the scaling advantages of
+community.
+In other words, testing should maximize the breadth of filesystem configuration
+scenarios and hardware setups.
+This improves code quality by enabling the authors of online fsck to find and
+fix bugs early, and helps developers of new features to find integration
+issues earlier in their development effort.
+
+The Linux filesystem community shares a common QA testing suite,
+`fstests <https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/>`_, for
+functional and regression testing.
+Even before development work began on online fsck, fstests (when run on XFS)
+would run both the ``xfs_check`` and ``xfs_repair -n`` commands on the test and
+scratch filesystems between each test.
+This provides a level of assurance that the kernel and the fsck tools stay in
+alignment about what constitutes consistent metadata.
+During development of the online checking code, fstests was modified to run
+``xfs_scrub -n`` between each test to ensure that the new checking code
+produces the same results as the two existing fsck tools.
+
+To start development of online repair, fstests was modified to run
+``xfs_repair`` to rebuild the filesystem's metadata indices between tests.
+This ensures that offline repair does not crash, leave a corrupt filesystem
+after it exists, or trigger complaints from the online check.
+This also established a baseline for what can and cannot be repaired offline.
+To complete the first phase of development of online repair, fstests was
+modified to be able to run ``xfs_scrub`` in a "force rebuild" mode.
+This enables a comparison of the effectiveness of online repair as compared to
+the existing offline repair tools.
+
+General Fuzz Testing of Metadata Blocks
+---------------------------------------
+
+XFS benefits greatly from having a very robust debugging tool, ``xfs_db``.
+
+Before development of online fsck even began, a set of fstests were created
+to test the rather common fault that entire metadata blocks get corrupted.
+This required the creation of fstests library code that can create a filesystem
+containing every possible type of metadata object.
+Next, individual test cases were created to create a test filesystem, identify
+a single block of a specific type of metadata object, trash it with the
+existing ``blocktrash`` command in ``xfs_db``, and test the reaction of a
+particular metadata validation strategy.
+
+This earlier test suite enabled XFS developers to test the ability of the
+in-kernel validation functions and the ability of the offline fsck tool to
+detect and eliminate the inconsistent metadata.
+This part of the test suite was extended to cover online fsck in exactly the
+same manner.
+
+In other words, for a given fstests filesystem configuration:
+
+* For each metadata object existing on the filesystem:
+
+  * Write garbage to it
+
+  * Test the reactions of:
+
+    1. The kernel verifiers to stop obviously bad metadata
+    2. Offline repair (``xfs_repair``) to detect and fix
+    3. Online repair (``xfs_scrub``) to detect and fix
+
+Targeted Fuzz Testing of Metadata Records
+-----------------------------------------
+
+A quick conversation with the other XFS developers revealed that the existing
+test infrastructure could be extended to provide a much more powerful
+facility: targeted fuzz testing of every metadata field of every metadata
+object in the filesystem.
+``xfs_db`` can modify every field of every metadata structure in every
+block in the filesystem to simulate the effects of memory corruption and
+software bugs.
+Given that fstests already contains the ability to create a filesystem
+containing every metadata format known to the filesystem, ``xfs_db`` can be
+used to perform exhaustive fuzz testing!
+
+For a given fstests filesystem configuration:
+
+* For each metadata object existing on the filesystem...
+
+  * For each record inside that metadata object...
+
+    * For each field inside that record...
+
+      * For each conceivable type of transformation that can be applied to a bit field...
+
+        1. Clear all bits
+        2. Set all bits
+        3. Toggle the most significant bit
+        4. Toggle the middle bit
+        5. Toggle the least significant bit
+        6. Add a small quantity
+        7. Subtract a small quantity
+        8. Randomize the contents
+
+        * ...test the reactions of:
+
+          1. The kernel verifiers to stop obviously bad metadata
+          2. Offline checking (``xfs_repair -n``)
+          3. Offline repair (``xfs_repair``)
+          4. Online checking (``xfs_scrub -n``)
+          5. Online repair (``xfs_scrub``)
+          6. Both repair tools (``xfs_scrub`` and then ``xfs_repair`` if online repair doesn't succeed)
+
+This is quite the combinatoric explosion!
+
+Fortunately, having this much test coverage makes it easy for XFS developers to
+check the responses of XFS' fsck tools.
+Since the introduction of the fuzz testing framework, these tests have been
+used to discover incorrect repair code and missing functionality for entire
+classes of metadata objects in ``xfs_repair``.
+The enhanced testing was used to finalize the deprecation of ``xfs_check`` by
+confirming that ``xfs_repair`` could detect at least as many corruptions as
+the older tool.
+
+These tests have been very valuable for ``xfs_scrub`` in the same ways -- they
+allow the online fsck developers to compare online fsck against offline fsck,
+and they enable XFS developers to find deficiencies in the code base.
+
+Proposed patchsets include
+`general fuzzer improvements
+<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=fuzzer-improvements>`_,
+`fuzzing baselines
+<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=fuzz-baseline>`_,
+and `improvements in fuzz testing comprehensiveness
+<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=more-fuzz-testing>`_.
+
+Stress Testing
+--------------
+
+A unique requirement to online fsck is the ability to operate on a filesystem
+concurrently with regular workloads.
+Although it is of course impossible to run ``xfs_scrub`` with *zero* observable
+impact on the running system, the online repair code should never introduce
+inconsistencies into the filesystem metadata, and regular workloads should
+never notice resource starvation.
+To verify that these conditions are being met, fstests has been enhanced in
+the following ways:
+
+* For each scrub item type, create a test to exercise checking that item type
+  while running ``fsstress``.
+* For each scrub item type, create a test to exercise repairing that item type
+  while running ``fsstress``.
+* Race ``fsstress`` and ``xfs_scrub -n`` to ensure that checking the whole
+  filesystem doesn't cause problems.
+* Race ``fsstress`` and ``xfs_scrub`` in force-rebuild mode to ensure that
+  force-repairing the whole filesystem doesn't cause problems.
+* Race ``xfs_scrub`` in check and force-repair mode against ``fsstress`` while
+  freezing and thawing the filesystem.
+* Race ``xfs_scrub`` in check and force-repair mode against ``fsstress`` while
+  remounting the filesystem read-only and read-write.
+* The same, but running ``fsx`` instead of ``fsstress``.  (Not done yet?)
+
+Success is defined by the ability to run all of these tests without observing
+any unexpected filesystem shutdowns due to corrupted metadata, kernel hang
+check warnings, or any other sort of mischief.
+
+Proposed patchsets include `general stress testing
+<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=race-scrub-and-mount-state-changes>`_
+and the `evolution of existing per-function stress testing
+<https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfstests-dev.git/log/?h=refactor-scrub-stress>`_.
