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    Subject[PATCH v2 tip/core/rcu 07/10] ipc: Replace spin_unlock_wait() with lock/unlock pair
    Date
    There is no agreed-upon definition of spin_unlock_wait()'s semantics,
    and it appears that all callers could do just as well with a lock/unlock
    pair. This commit therefore replaces the spin_unlock_wait() call in
    exit_sem() with spin_lock() followed immediately by spin_unlock().
    This should be safe from a performance perspective because exit_sem()
    is rarely invoked in production.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Alan Stern <stern@rowland.harvard.edu>
    Cc: Andrea Parri <parri.andrea@gmail.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Acked-by: Manfred Spraul <manfred@colorfullife.com>
    ---
    ipc/sem.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/ipc/sem.c b/ipc/sem.c
    index 9e70cd7a17da..2570830e29fc 100644
    --- a/ipc/sem.c
    +++ b/ipc/sem.c
    @@ -2091,7 +2091,8 @@ void exit_sem(struct task_struct *tsk)
    * possibility where we exit while freeary() didn't
    * finish unlocking sem_undo_list.
    */
    - spin_unlock_wait(&ulp->lock);
    + spin_lock(&ulp->lock);
    + spin_unlock(&ulp->lock);
    rcu_read_unlock();
    break;
    }
    --
    2.5.2
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