ipc,msg: shorten critical region in msgrcv
do_msgrcv() is the last msg queue function that abuses the ipc lock Take it only when needed when actually updating msq. Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Rik van Riel <riel@redhat.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso
Linus Torvalds
Родитель
3dd1f784ed
Коммит
41a0d523d0
58
ipc/msg.c
58
ipc/msg.c
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@ -885,21 +885,19 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
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return ERR_PTR(-EAGAIN);
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}
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long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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int msgflg,
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long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgflg,
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long (*msg_handler)(void __user *, struct msg_msg *, size_t))
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{
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struct msg_queue *msq;
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struct msg_msg *msg;
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int mode;
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struct msg_queue *msq;
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struct ipc_namespace *ns;
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struct msg_msg *copy = NULL;
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struct msg_msg *msg, *copy = NULL;
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ns = current->nsproxy->ipc_ns;
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if (msqid < 0 || (long) bufsz < 0)
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return -EINVAL;
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if (msgflg & MSG_COPY) {
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copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax));
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if (IS_ERR(copy))
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@ -907,8 +905,10 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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}
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mode = convert_mode(&msgtyp, msgflg);
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msq = msg_lock_check(ns, msqid);
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rcu_read_lock();
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msq = msq_obtain_object_check(ns, msqid);
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if (IS_ERR(msq)) {
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rcu_read_unlock();
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free_copy(copy);
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return PTR_ERR(msq);
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}
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@ -918,10 +918,10 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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msg = ERR_PTR(-EACCES);
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if (ipcperms(ns, &msq->q_perm, S_IRUGO))
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goto out_unlock;
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goto out_unlock1;
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ipc_lock_object(&msq->q_perm);
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msg = find_msg(msq, &msgtyp, mode);
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if (!IS_ERR(msg)) {
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/*
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* Found a suitable message.
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@ -929,7 +929,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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*/
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if ((bufsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
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msg = ERR_PTR(-E2BIG);
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goto out_unlock;
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goto out_unlock0;
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}
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/*
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* If we are copying, then do not unlink message and do
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@ -937,8 +937,9 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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*/
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if (msgflg & MSG_COPY) {
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msg = copy_msg(msg, copy);
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goto out_unlock;
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goto out_unlock0;
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}
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list_del(&msg->m_list);
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msq->q_qnum--;
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msq->q_rtime = get_seconds();
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@ -947,14 +948,16 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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atomic_sub(msg->m_ts, &ns->msg_bytes);
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atomic_dec(&ns->msg_hdrs);
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ss_wakeup(&msq->q_senders, 0);
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msg_unlock(msq);
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break;
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goto out_unlock0;
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}
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/* No message waiting. Wait for a message */
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if (msgflg & IPC_NOWAIT) {
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msg = ERR_PTR(-ENOMSG);
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goto out_unlock;
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goto out_unlock0;
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}
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list_add_tail(&msr_d.r_list, &msq->q_receivers);
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msr_d.r_tsk = current;
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msr_d.r_msgtype = msgtyp;
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@ -965,8 +968,9 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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msr_d.r_maxsize = bufsz;
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msr_d.r_msg = ERR_PTR(-EAGAIN);
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current->state = TASK_INTERRUPTIBLE;
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msg_unlock(msq);
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ipc_unlock_object(&msq->q_perm);
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rcu_read_unlock();
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schedule();
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/* Lockless receive, part 1:
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@ -977,7 +981,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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* Prior to destruction, expunge_all(-EIRDM) changes r_msg.
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* Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
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* rcu_read_lock() prevents preemption between reading r_msg
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* and the spin_lock() inside ipc_lock_by_ptr().
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* and acquiring the q_perm.lock in ipc_lock_object().
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*/
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rcu_read_lock();
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@ -996,32 +1000,34 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
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* If there is a message or an error then accept it without
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* locking.
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*/
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if (msg != ERR_PTR(-EAGAIN)) {
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rcu_read_unlock();
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break;
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}
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if (msg != ERR_PTR(-EAGAIN))
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goto out_unlock1;
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/* Lockless receive, part 3:
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* Acquire the queue spinlock.
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*/
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ipc_lock_by_ptr(&msq->q_perm);
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rcu_read_unlock();
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ipc_lock_object(&msq->q_perm);
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/* Lockless receive, part 4:
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* Repeat test after acquiring the spinlock.
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*/
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msg = (struct msg_msg*)msr_d.r_msg;
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if (msg != ERR_PTR(-EAGAIN))
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goto out_unlock;
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goto out_unlock0;
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list_del(&msr_d.r_list);
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if (signal_pending(current)) {
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msg = ERR_PTR(-ERESTARTNOHAND);
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out_unlock:
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msg_unlock(msq);
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break;
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goto out_unlock0;
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}
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ipc_unlock_object(&msq->q_perm);
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}
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out_unlock0:
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ipc_unlock_object(&msq->q_perm);
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out_unlock1:
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rcu_read_unlock();
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if (IS_ERR(msg)) {
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free_copy(copy);
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return PTR_ERR(msg);
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