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Diffstat (limited to 'ipc/msg.c')
-rw-r--r--ipc/msg.c62
1 files changed, 46 insertions, 16 deletions
diff --git a/ipc/msg.c b/ipc/msg.c
index 8dec945fa030..caca67368cb5 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -61,6 +61,16 @@ struct msg_queue {
struct list_head q_senders;
} __randomize_layout;
+/*
+ * MSG_BARRIER Locking:
+ *
+ * Similar to the optimization used in ipc/mqueue.c, one syscall return path
+ * does not acquire any locks when it sees that a message exists in
+ * msg_receiver.r_msg. Therefore r_msg is set using smp_store_release()
+ * and accessed using READ_ONCE()+smp_acquire__after_ctrl_dep(). In addition,
+ * wake_q_add_safe() is used. See ipc/mqueue.c for more details
+ */
+
/* one msg_receiver structure for each sleeping receiver */
struct msg_receiver {
struct list_head r_list;
@@ -184,6 +194,10 @@ static inline void ss_add(struct msg_queue *msq,
{
mss->tsk = current;
mss->msgsz = msgsz;
+ /*
+ * No memory barrier required: we did ipc_lock_object(),
+ * and the waker obtains that lock before calling wake_q_add().
+ */
__set_current_state(TASK_INTERRUPTIBLE);
list_add_tail(&mss->list, &msq->q_senders);
}
@@ -237,8 +251,11 @@ static void expunge_all(struct msg_queue *msq, int res,
struct msg_receiver *msr, *t;
list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
- wake_q_add(wake_q, msr->r_tsk);
- WRITE_ONCE(msr->r_msg, ERR_PTR(res));
+ get_task_struct(msr->r_tsk);
+
+ /* see MSG_BARRIER for purpose/pairing */
+ smp_store_release(&msr->r_msg, ERR_PTR(res));
+ wake_q_add_safe(wake_q, msr->r_tsk);
}
}
@@ -377,7 +394,7 @@ copy_msqid_from_user(struct msqid64_ds *out, void __user *buf, int version)
* NOTE: no locks must be held, the rwsem is taken inside this function.
*/
static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
- struct msqid64_ds *msqid64)
+ struct ipc64_perm *perm, int msg_qbytes)
{
struct kern_ipc_perm *ipcp;
struct msg_queue *msq;
@@ -387,7 +404,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
rcu_read_lock();
ipcp = ipcctl_obtain_check(ns, &msg_ids(ns), msqid, cmd,
- &msqid64->msg_perm, msqid64->msg_qbytes);
+ perm, msg_qbytes);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
goto out_unlock1;
@@ -409,18 +426,18 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
{
DEFINE_WAKE_Q(wake_q);
- if (msqid64->msg_qbytes > ns->msg_ctlmnb &&
+ if (msg_qbytes > ns->msg_ctlmnb &&
!capable(CAP_SYS_RESOURCE)) {
err = -EPERM;
goto out_unlock1;
}
ipc_lock_object(&msq->q_perm);
- err = ipc_update_perm(&msqid64->msg_perm, ipcp);
+ err = ipc_update_perm(perm, ipcp);
if (err)
goto out_unlock0;
- msq->q_qbytes = msqid64->msg_qbytes;
+ msq->q_qbytes = msg_qbytes;
msq->q_ctime = ktime_get_real_seconds();
/*
@@ -601,9 +618,10 @@ static long ksys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf, int ver
case IPC_SET:
if (copy_msqid_from_user(&msqid64, buf, version))
return -EFAULT;
- /* fallthru */
+ return msgctl_down(ns, msqid, cmd, &msqid64.msg_perm,
+ msqid64.msg_qbytes);
case IPC_RMID:
- return msgctl_down(ns, msqid, cmd, &msqid64);
+ return msgctl_down(ns, msqid, cmd, NULL, 0);
default:
return -EINVAL;
}
@@ -735,9 +753,9 @@ static long compat_ksys_msgctl(int msqid, int cmd, void __user *uptr, int versio
case IPC_SET:
if (copy_compat_msqid_from_user(&msqid64, uptr, version))
return -EFAULT;
- /* fallthru */
+ return msgctl_down(ns, msqid, cmd, &msqid64.msg_perm, msqid64.msg_qbytes);
case IPC_RMID:
- return msgctl_down(ns, msqid, cmd, &msqid64);
+ return msgctl_down(ns, msqid, cmd, NULL, 0);
default:
return -EINVAL;
}
@@ -798,13 +816,17 @@ static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg,
list_del(&msr->r_list);
if (msr->r_maxsize < msg->m_ts) {
wake_q_add(wake_q, msr->r_tsk);
- WRITE_ONCE(msr->r_msg, ERR_PTR(-E2BIG));
+
+ /* See expunge_all regarding memory barrier */
+ smp_store_release(&msr->r_msg, ERR_PTR(-E2BIG));
} else {
ipc_update_pid(&msq->q_lrpid, task_pid(msr->r_tsk));
msq->q_rtime = ktime_get_real_seconds();
wake_q_add(wake_q, msr->r_tsk);
- WRITE_ONCE(msr->r_msg, msg);
+
+ /* See expunge_all regarding memory barrier */
+ smp_store_release(&msr->r_msg, msg);
return 1;
}
}
@@ -1154,7 +1176,11 @@ static long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, in
msr_d.r_maxsize = INT_MAX;
else
msr_d.r_maxsize = bufsz;
- msr_d.r_msg = ERR_PTR(-EAGAIN);
+
+ /* memory barrier not require due to ipc_lock_object() */
+ WRITE_ONCE(msr_d.r_msg, ERR_PTR(-EAGAIN));
+
+ /* memory barrier not required, we own ipc_lock_object() */
__set_current_state(TASK_INTERRUPTIBLE);
ipc_unlock_object(&msq->q_perm);
@@ -1183,8 +1209,12 @@ static long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, in
* signal) it will either see the message and continue ...
*/
msg = READ_ONCE(msr_d.r_msg);
- if (msg != ERR_PTR(-EAGAIN))
+ if (msg != ERR_PTR(-EAGAIN)) {
+ /* see MSG_BARRIER for purpose/pairing */
+ smp_acquire__after_ctrl_dep();
+
goto out_unlock1;
+ }
/*
* ... or see -EAGAIN, acquire the lock to check the message
@@ -1192,7 +1222,7 @@ static long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, in
*/
ipc_lock_object(&msq->q_perm);
- msg = msr_d.r_msg;
+ msg = READ_ONCE(msr_d.r_msg);
if (msg != ERR_PTR(-EAGAIN))
goto out_unlock0;