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    SubjectRe: [PATCH 1/2] security/apparmor: Replace homebrew use of write_can_lock with lockdep
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    On 10/03/2017 07:32 AM, Will Deacon wrote:
    > The lockdep subsystem provides a robust way to assert that a lock is
    > held, so use that instead of write_can_lock, which can give incorrect
    > results for qrwlocks.
    >
    > Cc: John Johansen <john.johansen@canonical.com>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Signed-off-by: Will Deacon <will.deacon@arm.com>

    oh nice,

    Acked-by: John Johansen <john.johansen@canonical.com>



    > ---
    > security/apparmor/include/lib.h | 11 -----------
    > security/apparmor/label.c | 8 ++++----
    > 2 files changed, 4 insertions(+), 15 deletions(-)
    >
    > diff --git a/security/apparmor/include/lib.h b/security/apparmor/include/lib.h
    > index 436b3a722357..f546707a2bbb 100644
    > --- a/security/apparmor/include/lib.h
    > +++ b/security/apparmor/include/lib.h
    > @@ -19,17 +19,6 @@
    >
    > #include "match.h"
    >
    > -/* Provide our own test for whether a write lock is held for asserts
    > - * this is because on none SMP systems write_can_lock will always
    > - * resolve to true, which is what you want for code making decisions
    > - * based on it, but wrong for asserts checking that the lock is held
    > - */
    > -#ifdef CONFIG_SMP
    > -#define write_is_locked(X) !write_can_lock(X)
    > -#else
    > -#define write_is_locked(X) (1)
    > -#endif /* CONFIG_SMP */
    > -
    > /*
    > * DEBUG remains global (no per profile flag) since it is mostly used in sysctl
    > * which is not related to profile accesses.
    > diff --git a/security/apparmor/label.c b/security/apparmor/label.c
    > index c5b99b954580..ad28e03a6f30 100644
    > --- a/security/apparmor/label.c
    > +++ b/security/apparmor/label.c
    > @@ -80,7 +80,7 @@ void __aa_proxy_redirect(struct aa_label *orig, struct aa_label *new)
    >
    > AA_BUG(!orig);
    > AA_BUG(!new);
    > - AA_BUG(!write_is_locked(&labels_set(orig)->lock));
    > + lockdep_assert_held_exclusive(&labels_set(orig)->lock);
    >
    > tmp = rcu_dereference_protected(orig->proxy->label,
    > &labels_ns(orig)->lock);
    > @@ -571,7 +571,7 @@ static bool __label_remove(struct aa_label *label, struct aa_label *new)
    >
    > AA_BUG(!ls);
    > AA_BUG(!label);
    > - AA_BUG(!write_is_locked(&ls->lock));
    > + lockdep_assert_held_exclusive(&ls->lock);
    >
    > if (new)
    > __aa_proxy_redirect(label, new);
    > @@ -608,7 +608,7 @@ static bool __label_replace(struct aa_label *old, struct aa_label *new)
    > AA_BUG(!ls);
    > AA_BUG(!old);
    > AA_BUG(!new);
    > - AA_BUG(!write_is_locked(&ls->lock));
    > + lockdep_assert_held_exclusive(&ls->lock);
    > AA_BUG(new->flags & FLAG_IN_TREE);
    >
    > if (!label_is_stale(old))
    > @@ -645,7 +645,7 @@ static struct aa_label *__label_insert(struct aa_labelset *ls,
    > AA_BUG(!ls);
    > AA_BUG(!label);
    > AA_BUG(labels_set(label) != ls);
    > - AA_BUG(!write_is_locked(&ls->lock));
    > + lockdep_assert_held_exclusive(&ls->lock);
    > AA_BUG(label->flags & FLAG_IN_TREE);
    >
    > /* Figure out where to put new node */
    >

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