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    Subject[PATCH] locking/qrwlock: queued_write_lock_slowpath() cleanup
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    Make the code more readable by replacing the atomic_cmpxchg_acquire()
    by an equivalent atomic_try_cmpxchg_acquire() and change atomic_add()
    to atomic_or().

    For architectures that use qrwlock, I do not find one that has an
    atomic_add() defined but not an atomic_or(). I guess it should be fine
    by changing atomic_add() to atomic_or().

    Note that the previous use of atomic_add() isn't wrong as only one
    writer that is the wait_lock owner can set the waiting flag and the
    flag will be cleared later on when acquiring the write lock.

    Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Waiman Long <longman@redhat.com>
    ---
    kernel/locking/qrwlock.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
    index b94f3831e963..ec36b73f4733 100644
    --- a/kernel/locking/qrwlock.c
    +++ b/kernel/locking/qrwlock.c
    @@ -66,12 +66,12 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
    arch_spin_lock(&lock->wait_lock);

    /* Try to acquire the lock directly if no reader is present */
    - if (!atomic_read(&lock->cnts) &&
    - (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
    + if (!(cnts = atomic_read(&lock->cnts)) &&
    + atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))
    goto unlock;

    /* Set the waiting flag to notify readers that a writer is pending */
    - atomic_add(_QW_WAITING, &lock->cnts);
    + atomic_or(_QW_WAITING, &lock->cnts);

    /* When no more readers or writers, set the locked flag */
    do {
    --
    2.18.1
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