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    Subject[ 37/69] ipc,msg: make msgctl_nolock lockless
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Davidlohr Bueso <davidlohr.bueso@hp.com>

    commit ac0ba20ea6f2201a1589d6dc26ad1a4f0f967bb8 upstream.

    While the INFO cmd doesn't take the ipc lock, the STAT commands do
    acquire it unnecessarily. We can do the permissions and security checks
    only holding the rcu lock.

    This function now mimics semctl_nolock().

    Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    Cc: Rik van Riel <riel@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mike Galbraith <efault@gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    ipc/msg.c | 27 +++++++++++++++++----------
    1 file changed, 17 insertions(+), 10 deletions(-)

    --- a/ipc/msg.c
    +++ b/ipc/msg.c
    @@ -545,17 +545,25 @@ static int msgctl_nolock(struct ipc_name
    if (!buf)
    return -EFAULT;

    + memset(&tbuf, 0, sizeof(tbuf));
    +
    + rcu_read_lock();
    if (cmd == MSG_STAT) {
    - msq = msg_lock(ns, msqid);
    - if (IS_ERR(msq))
    - return PTR_ERR(msq);
    + msq = msq_obtain_object(ns, msqid);
    + if (IS_ERR(msq)) {
    + err = PTR_ERR(msq);
    + goto out_unlock;
    + }
    success_return = msq->q_perm.id;
    } else {
    - msq = msg_lock_check(ns, msqid);
    - if (IS_ERR(msq))
    - return PTR_ERR(msq);
    + msq = msq_obtain_object_check(ns, msqid);
    + if (IS_ERR(msq)) {
    + err = PTR_ERR(msq);
    + goto out_unlock;
    + }
    success_return = 0;
    }
    +
    err = -EACCES;
    if (ipcperms(ns, &msq->q_perm, S_IRUGO))
    goto out_unlock;
    @@ -564,8 +572,6 @@ static int msgctl_nolock(struct ipc_name
    if (err)
    goto out_unlock;

    - memset(&tbuf, 0, sizeof(tbuf));
    -
    kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
    tbuf.msg_stime = msq->q_stime;
    tbuf.msg_rtime = msq->q_rtime;
    @@ -575,7 +581,8 @@ static int msgctl_nolock(struct ipc_name
    tbuf.msg_qbytes = msq->q_qbytes;
    tbuf.msg_lspid = msq->q_lspid;
    tbuf.msg_lrpid = msq->q_lrpid;
    - msg_unlock(msq);
    + rcu_read_unlock();
    +
    if (copy_msqid_to_user(buf, &tbuf, version))
    return -EFAULT;
    return success_return;
    @@ -587,7 +594,7 @@ static int msgctl_nolock(struct ipc_name

    return err;
    out_unlock:
    - msg_unlock(msq);
    + rcu_read_unlock();
    return err;
    }




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