diff options
Diffstat (limited to 'ipc')
| -rw-r--r-- | ipc/msg.c | 43 |
1 files changed, 36 insertions, 7 deletions
diff --git a/ipc/msg.c b/ipc/msg.c index 8dec945fa030..82ca36bac13e 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); } } @@ -798,13 +815,17 @@ 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 +1175,11 @@ 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 +1208,12 @@ 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 +1221,7 @@ 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; |