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    Subject[PATCH v2 1/3] lockdep: add lockdep_assert_not_held()
    Date
    Some kernel functions must be called without holding a specific lock.
    Add lockdep_assert_not_held() to be used in these functions to detect
    incorrect calls while holding a lock.

    lockdep_assert_not_held() provides the opposite functionality of
    lockdep_assert_held() which is used to assert calls that require
    holding a specific lock.

    Incorporates suggestions from Peter Zijlstra to avoid misfires when
    lockdep_off() is employed.

    The need for lockdep_assert_not_held() came up in a discussion on
    ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
    of functions that can use lockdep_assert_not_held().

    Link: https://lore.kernel.org/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@linuxfoundation.org/
    Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
    Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
    ---
    include/linux/lockdep.h | 11 ++++++++---
    kernel/locking/lockdep.c | 5 ++++-
    2 files changed, 12 insertions(+), 4 deletions(-)

    diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
    index b9e9adec73e8..93eb5f797fc1 100644
    --- a/include/linux/lockdep.h
    +++ b/include/linux/lockdep.h
    @@ -294,8 +294,12 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);

    #define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)

    -#define lockdep_assert_held(l) do { \
    - WARN_ON(debug_locks && !lockdep_is_held(l)); \
    +#define lockdep_assert_held(l) do { \
    + WARN_ON(debug_locks && lockdep_is_held(l) == 0); \
    + } while (0)
    +
    +#define lockdep_assert_not_held(l) do { \
    + WARN_ON(debug_locks && lockdep_is_held(l) == 1); \
    } while (0)

    #define lockdep_assert_held_write(l) do { \
    @@ -384,7 +388,8 @@ extern int lockdep_is_held(const void *);
    #define lockdep_is_held_type(l, r) (1)

    #define lockdep_assert_held(l) do { (void)(l); } while (0)
    -#define lockdep_assert_held_write(l) do { (void)(l); } while (0)
    +#define lockdep_assert_not_held(l) do { (void)(l); } while (0)
    +#define lockdep_assert_held_write(l) do { (void)(l); } while (0)
    #define lockdep_assert_held_read(l) do { (void)(l); } while (0)
    #define lockdep_assert_held_once(l) do { (void)(l); } while (0)

    diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
    index bdaf4829098c..d3299fd85c4a 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -5472,7 +5472,10 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
    int ret = 0;

    if (unlikely(!lockdep_enabled()))
    - return 1; /* avoid false negative lockdep_assert_held() */
    + /* avoid false negative lockdep_assert_not_held()
    + * and lockdep_assert_held()
    + */
    + return -1;

    raw_local_irq_save(flags);
    check_flags(flags);
    --
    2.27.0
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