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doc: clarify (un)load hook execution context

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This commit is contained in:
Joe Lawrence 2017-03-23 16:13:38 -04:00
parent 87e264dfa2
commit d072845816
1 changed files with 10 additions and 2 deletions
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doc/patch-author-guide.md
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@ -113,8 +113,16 @@ patch module is loaded.
`kpatch-macros.h` provides `KPATCH_LOAD_HOOK` and `KPATCH_UNLOAD_HOOK` macros
to define such functions. The signature of both hook functions is `void
foo(void)` and and they may run in `stop_machine` context (so they must not
sleep).
foo(void)`. Their execution context is as follows:
* For patches to vmlinux or already loaded kernel modules, hook functions
will be run by `stop_machine` as part of applying or removing a patch.
(Therefore the hooks must not block or sleep.)
* For patches to kernel modules which haven't been loaded yet, a
module-notifier will execute load hooks when the associated module is loaded
into the `MODULE_STATE_COMING` state. The load hook is called before any
module_init code.
Example: a kpatch fix for CVE-2016-5389 utilized the `KPATCH_LOAD_HOOK` and
`KPATCH_UNLOAD_HOOK` macros to modify variable `sysctl_tcp_challenge_ack_limit`