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    Subject[PATCH 5/7] ipc,sem: open code and rename sem_lock
    Date
    Rename sem_lock to sem_obtain_lock, so we can introduce a sem_lock
    function later that only locks the sem_array and does nothing else.

    Open code the locking from ipc_lock in sem_obtain_lock, so we can
    introduce finer grained locking for the sem_array in the next patch.

    Signed-off-by: Rik van Riel <riel@redhat.com>
    ---
    ipc/sem.c | 23 +++++++++++++++++++----
    1 files changed, 19 insertions(+), 4 deletions(-)

    diff --git a/ipc/sem.c b/ipc/sem.c
    index ff3d4ff..d25f9b6 100644
    --- a/ipc/sem.c
    +++ b/ipc/sem.c
    @@ -194,14 +194,29 @@ void __init sem_init (void)
    * sem_lock_(check_) routines are called in the paths where the rw_mutex
    * is not held.
    */
    -static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
    +static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns, int id)
    {
    - struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id);
    + struct kern_ipc_perm *ipcp;

    + rcu_read_lock();
    + ipcp = ipc_obtain_object(&sem_ids(ns), id);
    if (IS_ERR(ipcp))
    - return (struct sem_array *)ipcp;
    + goto err1;
    +
    + spin_lock(&ipcp->lock);
    +
    + /* ipc_rmid() may have already freed the ID while sem_lock
    + * was spinning: verify that the structure is still valid
    + */
    + if (ipcp->deleted)
    + goto err0;

    return container_of(ipcp, struct sem_array, sem_perm);
    +err0:
    + spin_unlock(&ipcp->lock);
    +err1:
    + rcu_read_unlock();
    + return ERR_PTR(-EINVAL);
    }

    static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
    @@ -1562,7 +1577,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
    goto out_free;
    }

    - sma = sem_lock(ns, semid);
    + sma = sem_obtain_lock(ns, semid);

    /*
    * Wait until it's guaranteed that no wakeup_sem_queue_do() is ongoing.
    --
    1.7.7.6


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