Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 605 insertions, 0 deletions

diff --git a/Documentation/livepatch/callbacks.txt b/Documentation/livepatch/callbacks.txt
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+======================
+(Un)patching Callbacks
+======================
+
+Livepatch (un)patch-callbacks provide a mechanism for livepatch modules
+to execute callback functions when a kernel object is (un)patched.  They
+can be considered a "power feature" that extends livepatching abilities
+to include:
+
+  - Safe updates to global data
+
+  - "Patches" to init and probe functions
+
+  - Patching otherwise unpatchable code (i.e. assembly)
+
+In most cases, (un)patch callbacks will need to be used in conjunction
+with memory barriers and kernel synchronization primitives, like
+mutexes/spinlocks, or even stop_machine(), to avoid concurrency issues.
+
+Callbacks differ from existing kernel facilities:
+
+  - Module init/exit code doesn't run when disabling and re-enabling a
+    patch.
+
+  - A module notifier can't stop a to-be-patched module from loading.
+
+Callbacks are part of the klp_object structure and their implementation
+is specific to that klp_object.  Other livepatch objects may or may not
+be patched, irrespective of the target klp_object's current state.
+
+Callbacks can be registered for the following livepatch actions:
+
+  * Pre-patch    - before a klp_object is patched
+
+  * Post-patch   - after a klp_object has been patched and is active
+                   across all tasks
+
+  * Pre-unpatch  - before a klp_object is unpatched (ie, patched code is
+                   active), used to clean up post-patch callback
+                   resources
+
+  * Post-unpatch - after a klp_object has been patched, all code has
+                   been restored and no tasks are running patched code,
+                   used to cleanup pre-patch callback resources
+
+Each callback is optional, omitting one does not preclude specifying any
+other.  However, the livepatching core executes the handlers in
+symmetry: pre-patch callbacks have a post-unpatch counterpart and
+post-patch callbacks have a pre-unpatch counterpart.  An unpatch
+callback will only be executed if its corresponding patch callback was
+executed.  Typical use cases pair a patch handler that acquires and
+configures resources with an unpatch handler tears down and releases
+those same resources.
+
+A callback is only executed if its host klp_object is loaded.  For
+in-kernel vmlinux targets, this means that callbacks will always execute
+when a livepatch is enabled/disabled.  For patch target kernel modules,
+callbacks will only execute if the target module is loaded.  When a
+module target is (un)loaded, its callbacks will execute only if the
+livepatch module is enabled.
+
+The pre-patch callback, if specified, is expected to return a status
+code (0 for success, -ERRNO on error).  An error status code indicates
+to the livepatching core that patching of the current klp_object is not
+safe and to stop the current patching request.  (When no pre-patch
+callback is provided, the transition is assumed to be safe.)  If a
+pre-patch callback returns failure, the kernel's module loader will:
+
+  - Refuse to load a livepatch, if the livepatch is loaded after
+    targeted code.
+
+    or:
+
+  - Refuse to load a module, if the livepatch was already successfully
+    loaded.
+
+No post-patch, pre-unpatch, or post-unpatch callbacks will be executed
+for a given klp_object if the object failed to patch, due to a failed
+pre_patch callback or for any other reason.
+
+If a patch transition is reversed, no pre-unpatch handlers will be run
+(this follows the previously mentioned symmetry -- pre-unpatch callbacks
+will only occur if their corresponding post-patch callback executed).
+
+If the object did successfully patch, but the patch transition never
+started for some reason (e.g., if another object failed to patch),
+only the post-unpatch callback will be called.
+
+
+Example Use-cases
+=================
+
+Update global data
+------------------
+
+A pre-patch callback can be useful to update a global variable.  For
+example, 75ff39ccc1bd ("tcp: make challenge acks less predictable")
+changes a global sysctl, as well as patches the tcp_send_challenge_ack()
+function.
+
+In this case, if we're being super paranoid, it might make sense to
+patch the data *after* patching is complete with a post-patch callback,
+so that tcp_send_challenge_ack() could first be changed to read
+sysctl_tcp_challenge_ack_limit with READ_ONCE.
+
+
+Support __init and probe function patches
+-----------------------------------------
+
+Although __init and probe functions are not directly livepatch-able, it
+may be possible to implement similar updates via pre/post-patch
+callbacks.
+
+48900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST") change the way that
+virtnet_probe() initialized its driver's net_device features.  A
+pre/post-patch callback could iterate over all such devices, making a
+similar change to their hw_features value.  (Client functions of the
+value may need to be updated accordingly.)
+
+
+Test cases
+==========
+
+What follows is not an exhaustive test suite of every possible livepatch
+pre/post-(un)patch combination, but a selection that demonstrates a few
+important concepts.  Each test case uses the kernel modules located in
+the samples/livepatch/ and assumes that no livepatches are loaded at the
+beginning of the test.
+
+
+Test 1
+------
+
+Test a combination of loading a kernel module and a livepatch that
+patches a function in the first module.  (Un)load the target module
+before the livepatch module:
+
+- load target module
+- load livepatch
+- disable livepatch
+- unload target module
+- unload livepatch
+
+First load a target module:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   34.475708] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+On livepatch enable, before the livepatch transition starts, pre-patch
+callbacks are executed for vmlinux and livepatch_callbacks_mod (those
+klp_objects currently loaded).  After klp_objects are patched according
+to the klp_patch, their post-patch callbacks run and the transition
+completes:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   36.503719] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   36.504213] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   36.504238] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   36.504721] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   36.505849] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   37.727133] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   37.727232] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   37.727860] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   37.728792] livepatch: 'livepatch_callbacks_demo': patching complete
+
+Similarly, on livepatch disable, pre-patch callbacks run before the
+unpatching transition starts.  klp_objects are reverted, post-patch
+callbacks execute and the transition completes:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   38.510209] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   38.510234] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   38.510982] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   38.512209] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   39.711132] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   39.711210] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   39.711779] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   39.712735] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   42.534183] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+
+
+Test 2
+------
+
+This test is similar to the previous test, but (un)load the livepatch
+module before the target kernel module.  This tests the livepatch core's
+module_coming handler:
+
+- load livepatch
+- load target module
+- disable livepatch
+- unload livepatch
+- unload target module
+
+
+On livepatch enable, only pre/post-patch callbacks are executed for
+currently loaded klp_objects, in this case, vmlinux:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   44.553328] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   44.553997] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   44.554049] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   44.554845] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   45.727128] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   45.727212] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   45.727961] livepatch: 'livepatch_callbacks_demo': patching complete
+
+When a targeted module is subsequently loaded, only its pre/post-patch
+callbacks are executed:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   46.560845] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
+  [   46.561988] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [   46.563452] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [   46.565495] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+On livepatch disable, all currently loaded klp_objects' (vmlinux and
+livepatch_callbacks_mod) pre/post-unpatch callbacks are executed:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   48.568885] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   48.568910] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   48.569441] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   48.570502] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   49.759091] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   49.759171] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   49.759742] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   49.760690] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   52.592283] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+
+
+Test 3
+------
+
+Test loading the livepatch after a targeted kernel module, then unload
+the kernel module before disabling the livepatch.  This tests the
+livepatch core's module_going handler:
+
+- load target module
+- load livepatch
+- unload target module
+- disable livepatch
+- unload livepatch
+
+First load a target module, then the livepatch:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   54.607948] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   56.613919] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   56.614411] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   56.614436] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   56.614818] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   56.615656] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   57.759070] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   57.759147] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   57.759621] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_LIVE] Normal state
+  [   57.760307] livepatch: 'livepatch_callbacks_demo': patching complete
+
+When a target module is unloaded, the livepatch is only reverted from
+that klp_object (livepatch_callbacks_mod).  As such, only its pre and
+post-unpatch callbacks are executed when this occurs:
+
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   58.623409] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+  [   58.623903] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+  [   58.624658] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
+  [   58.625305] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+
+When the livepatch is disabled, pre and post-unpatch callbacks are run
+for the remaining klp_object, vmlinux:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   60.638420] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   60.638444] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   60.638996] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   61.727088] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   61.727165] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   61.727985] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+
+
+Test 4
+------
+
+This test is similar to the previous test, however the livepatch is
+loaded first.  This tests the livepatch core's module_coming and
+module_going handlers:
+
+- load livepatch
+- load target module
+- unload target module
+- disable livepatch
+- unload livepatch
+
+First load the livepatch:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   64.661552] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   64.662147] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   64.662175] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   64.662850] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   65.695056] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   65.695147] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   65.695561] livepatch: 'livepatch_callbacks_demo': patching complete
+
+When a targeted kernel module is subsequently loaded, only its
+pre/post-patch callbacks are executed:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   66.669196] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
+  [   66.669882] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [   66.670744] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [   66.672873] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+When the target module is unloaded, the livepatch is only reverted from
+the livepatch_callbacks_mod klp_object.  As such, only pre and
+post-unpatch callbacks are executed when this occurs:
+
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   68.680065] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+  [   68.680688] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+  [   68.681452] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
+  [   68.682094] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   70.689225] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   70.689256] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   70.689882] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   71.711080] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   71.711481] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   71.711988] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+
+
+Test 5
+------
+
+A simple test of loading a livepatch without one of its patch target
+klp_objects ever loaded (livepatch_callbacks_mod):
+
+- load livepatch
+- disable livepatch
+- unload livepatch
+
+Load the livepatch:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   74.711081] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   74.711595] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   74.711639] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   74.712272] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   75.743137] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   75.743219] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   75.743867] livepatch: 'livepatch_callbacks_demo': patching complete
+
+As expected, only pre/post-(un)patch handlers are executed for vmlinux:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   76.716254] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   76.716278] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   76.716666] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   77.727089] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   77.727194] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   77.727907] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+
+
+Test 6
+------
+
+Test a scenario where a vmlinux pre-patch callback returns a non-zero
+status (ie, failure):
+
+- load target module
+- load livepatch -ENODEV
+- unload target module
+
+First load a target module:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   80.740520] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+Load the livepatch module, setting its 'pre_patch_ret' value to -19
+(-ENODEV).  When its vmlinux pre-patch callback executed, this status
+code will propagate back to the module-loading subsystem.  The result is
+that the insmod command refuses to load the livepatch module:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko pre_patch_ret=-19
+  [   82.747326] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   82.747743] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   82.747767] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   82.748237] livepatch: pre-patch callback failed for object 'vmlinux'
+  [   82.748637] livepatch: failed to enable patch 'livepatch_callbacks_demo'
+  [   82.749059] livepatch: 'livepatch_callbacks_demo': canceling transition, going to unpatch
+  [   82.749060] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   82.749868] livepatch: 'livepatch_callbacks_demo': unpatching complete
+  [   82.765809] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-demo.ko: No such device
+
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   84.774238] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+
+
+Test 7
+------
+
+Similar to the previous test, setup a livepatch such that its vmlinux
+pre-patch callback returns success.  However, when a targeted kernel
+module is later loaded, have the livepatch return a failing status code:
+
+- load livepatch
+- setup -ENODEV
+- load target module
+- disable livepatch
+- unload livepatch
+
+Load the livepatch, notice vmlinux pre-patch callback succeeds:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   86.787845] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   86.788325] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   86.788427] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   86.788821] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   87.711069] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   87.711143] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   87.711886] livepatch: 'livepatch_callbacks_demo': patching complete
+
+Set a trap so subsequent pre-patch callbacks to this livepatch will
+return -ENODEV:
+
+  % echo -19 > /sys/module/livepatch_callbacks_demo/parameters/pre_patch_ret
+
+The livepatch pre-patch callback for subsequently loaded target modules
+will return failure, so the module loader refuses to load the kernel
+module.  Notice that no post-patch or pre/post-unpatch callbacks are
+executed for this klp_object:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [   90.796976] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
+  [   90.797834] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [   90.798900] livepatch: pre-patch callback failed for object 'livepatch_callbacks_mod'
+  [   90.799652] livepatch: patch 'livepatch_callbacks_demo' failed for module 'livepatch_callbacks_mod', refusing to load module 'livepatch_callbacks_mod'
+  [   90.819737] insmod: ERROR: could not insert module samples/livepatch/livepatch-callbacks-mod.ko: No such device
+
+However, pre/post-unpatch callbacks run for the vmlinux klp_object:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [   92.823547] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [   92.823573] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [   92.824331] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [   93.727128] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [   93.727327] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [   93.727861] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+
+
+Test 8
+------
+
+Test loading multiple targeted kernel modules.  This test-case is
+mainly for comparing with the next test-case.
+
+- load busy target module (0s sleep),
+- load livepatch
+- load target module
+- unload target module
+- disable livepatch
+- unload livepatch
+- unload busy target module
+
+
+Load a target "busy" kernel module which kicks off a worker function
+that immediately exits:
+
+  % insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=0
+  [   96.910107] livepatch_callbacks_busymod: livepatch_callbacks_mod_init
+  [   96.910600] livepatch_callbacks_busymod: busymod_work_func, sleeping 0 seconds ...
+  [   96.913024] livepatch_callbacks_busymod: busymod_work_func exit
+
+Proceed with loading the livepatch and another ordinary target module,
+notice that the post-patch callbacks are executed and the transition
+completes quickly:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [   98.917892] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [   98.918426] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [   98.918453] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [   98.918955] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [   98.923835] livepatch: 'livepatch_callbacks_demo': starting patching transition
+  [   99.743104] livepatch: 'livepatch_callbacks_demo': completing patching transition
+  [   99.743156] livepatch_callbacks_demo: post_patch_callback: vmlinux
+  [   99.743679] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [   99.744616] livepatch: 'livepatch_callbacks_demo': patching complete
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [  100.930955] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
+  [  100.931668] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [  100.932645] livepatch_callbacks_demo: post_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [  100.934125] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [  102.942805] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+  [  102.943640] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+  [  102.944585] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
+  [  102.945455] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [  104.953815] livepatch: 'livepatch_callbacks_demo': initializing unpatching transition
+  [  104.953838] livepatch_callbacks_demo: pre_unpatch_callback: vmlinux
+  [  104.954431] livepatch_callbacks_demo: pre_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [  104.955426] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [  106.719073] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [  106.722633] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [  106.723282] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [  106.724279] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+  % rmmod samples/livepatch/livepatch-callbacks-busymod.ko
+  [  108.975660] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit
+
+
+Test 9
+------
+
+A similar test as the previous one, but force the "busy" kernel module
+to do longer work.
+
+The livepatching core will refuse to patch a task that is currently
+executing a to-be-patched function -- the consistency model stalls the
+current patch transition until this safety-check is met.  Test a
+scenario where one of a livepatch's target klp_objects sits on such a
+function for a long time.  Meanwhile, load and unload other target
+kernel modules while the livepatch transition is in progress.
+
+- load busy target module (30s sleep)
+- load livepatch
+- load target module
+- unload target module
+- disable livepatch
+- unload livepatch
+- unload busy target module
+
+
+Load the "busy" kernel module, this time make it do 30 seconds worth of
+work:
+
+  % insmod samples/livepatch/livepatch-callbacks-busymod.ko sleep_secs=30
+  [  110.993362] livepatch_callbacks_busymod: livepatch_callbacks_mod_init
+  [  110.994059] livepatch_callbacks_busymod: busymod_work_func, sleeping 30 seconds ...
+
+Meanwhile, the livepatch is loaded.  Notice that the patch transition
+does not complete as the targeted "busy" module is sitting on a
+to-be-patched function:
+
+  % insmod samples/livepatch/livepatch-callbacks-demo.ko
+  [  113.000309] livepatch: enabling patch 'livepatch_callbacks_demo'
+  [  113.000764] livepatch: 'livepatch_callbacks_demo': initializing patching transition
+  [  113.000791] livepatch_callbacks_demo: pre_patch_callback: vmlinux
+  [  113.001289] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [  113.005208] livepatch: 'livepatch_callbacks_demo': starting patching transition
+
+Load a second target module (this one is an ordinary idle kernel
+module).  Note that *no* post-patch callbacks will be executed while the
+livepatch is still in transition:
+
+  % insmod samples/livepatch/livepatch-callbacks-mod.ko
+  [  115.012740] livepatch: applying patch 'livepatch_callbacks_demo' to loading module 'livepatch_callbacks_mod'
+  [  115.013406] livepatch_callbacks_demo: pre_patch_callback: livepatch_callbacks_mod -> [MODULE_STATE_COMING] Full formed, running module_init
+  [  115.015315] livepatch_callbacks_mod: livepatch_callbacks_mod_init
+
+Request an unload of the simple kernel module.  The patch is still
+transitioning, so its pre-unpatch callbacks are skipped:
+
+  % rmmod samples/livepatch/livepatch-callbacks-mod.ko
+  [  117.022626] livepatch_callbacks_mod: livepatch_callbacks_mod_exit
+  [  117.023376] livepatch: reverting patch 'livepatch_callbacks_demo' on unloading module 'livepatch_callbacks_mod'
+  [  117.024533] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_mod -> [MODULE_STATE_GOING] Going away
+
+Finally the livepatch is disabled.  Since none of the patch's
+klp_object's post-patch callbacks executed, the remaining klp_object's
+pre-unpatch callbacks are skipped:
+
+  % echo 0 > /sys/kernel/livepatch/livepatch_callbacks_demo/enabled
+  [  119.035408] livepatch: 'livepatch_callbacks_demo': reversing transition from patching to unpatching
+  [  119.035485] livepatch: 'livepatch_callbacks_demo': starting unpatching transition
+  [  119.711166] livepatch: 'livepatch_callbacks_demo': completing unpatching transition
+  [  119.714179] livepatch_callbacks_demo: post_unpatch_callback: vmlinux
+  [  119.714653] livepatch_callbacks_demo: post_unpatch_callback: livepatch_callbacks_busymod -> [MODULE_STATE_LIVE] Normal state
+  [  119.715437] livepatch: 'livepatch_callbacks_demo': unpatching complete
+
+  % rmmod samples/livepatch/livepatch-callbacks-demo.ko
+  % rmmod samples/livepatch/livepatch-callbacks-busymod.ko
+  [  141.279111] livepatch_callbacks_busymod: busymod_work_func exit
+  [  141.279760] livepatch_callbacks_busymod: livepatch_callbacks_mod_exit