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kernel-patches/for-mainline/rcu-locking-docs.txt

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Index: linux-2.6-apparmor/security/apparmor/locking.txt

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===================================================================

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--- linux-2.6-apparmor.orig/security/apparmor/locking.txt

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+++ linux-2.6-apparmor/security/apparmor/locking.txt

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@@ -15,15 +15,11 @@ Which lock protects what?

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        >-----------------------+-------------------------------<

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        | profile_list,         | profile_list_lock             |

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        +-----------------------+-------------------------------+

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+       | aa_profile            | (reference count)             |

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+       +-----------------------+-------------------------------+

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        | aa_profile->          | aa_profile->lock              |

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        |   isstale,            |                               |

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        |   task_contexts       |                               |

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-       | aa_profile->count     | RCU                           |

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-       +-----------------------+-------------------------------+

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-       | aa_task_context->     |                               |

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-       |   profile             | read: RCU                     |

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-       |                       | write: aa_profile->lock +     |

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-       |                       |        task_lock()            |

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        +-----------------------+-------------------------------+

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        | task_struct->security | read: RCU                     |

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        |                       | write: task_lock()            |

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@@ -39,8 +35,12 @@ When moving a task context from one prof

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 profile locks with lock_both_profiles(). This ensures that both locks

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 are always taken in the same order, and so we won't deadlock.

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-Since aa_task_struct->profile is RCU protected, it can change under a

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-reader at any time. Therefore, we should grab the pointer and use the

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-cached result, but we can only do this after all blocking operations (or

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-else the pointer could just change again). The ->profile pointer may

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-change or become NULL at any time; we must be careful about this.

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+Since task_struct->security is RCU protected the aa_task_struct it

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+references is only guarenteed to exist for the rcu cycle.  Where

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+aa_task_context->profile is needed in blocking operations the

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+profile's reference count is incremented and the profile reference

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+is used.

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+

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+Profiles on profile_list are never stale: when a profile becomes stale,

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+it is removed from profile_list at the same time (under profile_list_lock

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+and aa_profile->lock).

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