Commit 55cdbf47 authored by Manfred Spraul's avatar Manfred Spraul Committed by Linus Torvalds

[PATCH] cleanup of ipc/msg.c

Attached is a cleanup of the main loops in sys_msgrcv and sys_msgsnd, based on
ipc_lock_by_ptr().  Most backward gotos are gone, instead normal "for(;;)"
loops until a suitable message is found.

Description:

- General cleanup of sys_msgrcv and sys_msgsnd: the function were too
  convoluted.

- Enable lockless receive, update comments.

- Use ipc_getref for sys_msgsnd(), it's better than rechecking that the
  msqid is still valid.
Signed-Off-By: default avatarManfred Spraul <manfred@colorfullife.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 8dd459f2
......@@ -163,8 +163,10 @@ static void expunge_all(struct msg_queue* msq, int res)
msr = list_entry(tmp,struct msg_receiver,r_list);
tmp = tmp->next;
msr->r_msg = ERR_PTR(res);
msr->r_msg = NULL;
wake_up_process(msr->r_tsk);
smp_mb();
msr->r_msg = ERR_PTR(res);
}
}
/*
......@@ -525,13 +527,17 @@ static inline int pipelined_send(struct msg_queue* msq, struct msg_msg* msg)
!security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) {
list_del(&msr->r_list);
if(msr->r_maxsize < msg->m_ts) {
msr->r_msg = ERR_PTR(-E2BIG);
msr->r_msg = NULL;
wake_up_process(msr->r_tsk);
smp_mb();
msr->r_msg = ERR_PTR(-E2BIG);
} else {
msr->r_msg = msg;
msr->r_msg = NULL;
msq->q_lrpid = msr->r_tsk->pid;
msq->q_rtime = get_seconds();
wake_up_process(msr->r_tsk);
smp_mb();
msr->r_msg = msg;
return 1;
}
}
......@@ -564,43 +570,49 @@ asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz,
err=-EINVAL;
if(msq==NULL)
goto out_free;
retry:
err= -EIDRM;
if (msg_checkid(msq,msqid))
goto out_unlock_free;
err=-EACCES;
if (ipcperms(&msq->q_perm, S_IWUGO))
goto out_unlock_free;
for (;;) {
struct msg_sender s;
err = security_msg_queue_msgsnd(msq, msg, msgflg);
if (err)
goto out_unlock_free;
err=-EACCES;
if (ipcperms(&msq->q_perm, S_IWUGO))
goto out_unlock_free;
if(msgsz + msq->q_cbytes > msq->q_qbytes ||
1 + msq->q_qnum > msq->q_qbytes) {
struct msg_sender s;
err = security_msg_queue_msgsnd(msq, msg, msgflg);
if (err)
goto out_unlock_free;
if(msgsz + msq->q_cbytes <= msq->q_qbytes &&
1 + msq->q_qnum <= msq->q_qbytes) {
break;
}
/* queue full, wait: */
if(msgflg&IPC_NOWAIT) {
err=-EAGAIN;
goto out_unlock_free;
}
ss_add(msq, &s);
ipc_rcu_getref(msq);
msg_unlock(msq);
schedule();
current->state= TASK_RUNNING;
msq = msg_lock(msqid);
err = -EIDRM;
if(msq==NULL)
goto out_free;
ipc_lock_by_ptr(&msq->q_perm);
ipc_rcu_putref(msq);
if (msq->q_perm.deleted) {
err = -EIDRM;
goto out_unlock_free;
}
ss_del(&s);
if (signal_pending(current)) {
err=-EINTR;
err=-ERESTARTNOHAND;
goto out_unlock_free;
}
goto retry;
}
msq->q_lspid = current->tgid;
......@@ -649,10 +661,7 @@ asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
long msgtyp, int msgflg)
{
struct msg_queue *msq;
struct msg_receiver msr_d;
struct list_head* tmp;
struct msg_msg* msg, *found_msg;
int err;
struct msg_msg *msg;
int mode;
if (msqid < 0 || (long) msgsz < 0)
......@@ -662,62 +671,57 @@ asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
msq = msg_lock(msqid);
if(msq==NULL)
return -EINVAL;
retry:
err = -EIDRM;
msg = ERR_PTR(-EIDRM);
if (msg_checkid(msq,msqid))
goto out_unlock;
err=-EACCES;
if (ipcperms (&msq->q_perm, S_IRUGO))
goto out_unlock;
for (;;) {
struct msg_receiver msr_d;
struct list_head* tmp;
tmp = msq->q_messages.next;
found_msg=NULL;
while (tmp != &msq->q_messages) {
msg = list_entry(tmp,struct msg_msg,m_list);
if(testmsg(msg,msgtyp,mode) &&
!security_msg_queue_msgrcv(msq, msg, current, msgtyp, mode)) {
found_msg = msg;
if(mode == SEARCH_LESSEQUAL && msg->m_type != 1) {
found_msg=msg;
msgtyp=msg->m_type-1;
} else {
found_msg=msg;
break;
}
}
tmp = tmp->next;
}
if(found_msg) {
msg=found_msg;
if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
err=-E2BIG;
msg = ERR_PTR(-EACCES);
if (ipcperms (&msq->q_perm, S_IRUGO))
goto out_unlock;
msg = ERR_PTR(-EAGAIN);
tmp = msq->q_messages.next;
while (tmp != &msq->q_messages) {
struct msg_msg *walk_msg;
walk_msg = list_entry(tmp,struct msg_msg,m_list);
if(testmsg(walk_msg,msgtyp,mode) &&
!security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) {
msg = walk_msg;
if(mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) {
msg=walk_msg;
msgtyp=walk_msg->m_type-1;
} else {
msg=walk_msg;
break;
}
}
tmp = tmp->next;
}
list_del(&msg->m_list);
msq->q_qnum--;
msq->q_rtime = get_seconds();
msq->q_lrpid = current->tgid;
msq->q_cbytes -= msg->m_ts;
atomic_sub(msg->m_ts,&msg_bytes);
atomic_dec(&msg_hdrs);
ss_wakeup(&msq->q_senders,0);
msg_unlock(msq);
out_success:
msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
if (put_user (msg->m_type, &msgp->mtype) ||
store_msg(msgp->mtext, msg, msgsz)) {
msgsz = -EFAULT;
if(!IS_ERR(msg)) {
/* Found a suitable message. Unlink it from the queue. */
if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
msg = ERR_PTR(-E2BIG);
goto out_unlock;
}
list_del(&msg->m_list);
msq->q_qnum--;
msq->q_rtime = get_seconds();
msq->q_lrpid = current->tgid;
msq->q_cbytes -= msg->m_ts;
atomic_sub(msg->m_ts,&msg_bytes);
atomic_dec(&msg_hdrs);
ss_wakeup(&msq->q_senders,0);
msg_unlock(msq);
break;
}
free_msg(msg);
return msgsz;
} else
{
/* no message waiting. Prepare for pipelined
* receive.
*/
/* No message waiting. Wait for a message */
if (msgflg & IPC_NOWAIT) {
err=-ENOMSG;
msg = ERR_PTR(-ENOMSG);
goto out_unlock;
}
list_add_tail(&msr_d.r_list,&msq->q_receivers);
......@@ -727,52 +731,76 @@ asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
if(msgflg & MSG_NOERROR)
msr_d.r_maxsize = INT_MAX;
else
msr_d.r_maxsize = msgsz;
msr_d.r_maxsize = msgsz;
msr_d.r_msg = ERR_PTR(-EAGAIN);
current->state = TASK_INTERRUPTIBLE;
msg_unlock(msq);
schedule();
/*
* The below optimisation is buggy. A sleeping thread that is
* woken up checks if it got a message and if so, copies it to
* userspace and just returns without taking any locks.
* But this return to user space can be faster than the message
* send, and if the receiver immediately exits the
* wake_up_process performed by the sender will oops.
/* Lockless receive, part 1:
* Disable preemption. We don't hold a reference to the queue
* and getting a reference would defeat the idea of a lockless
* operation, thus the code relies on rcu to guarantee the
* existance of msq:
* Prior to destruction, expunge_all(-EIRDM) changes r_msg.
* Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
* rcu_read_lock() prevents preemption between reading r_msg
* and the spin_lock() inside ipc_lock_by_ptr().
*/
rcu_read_lock();
/* Lockless receive, part 2:
* Wait until pipelined_send or expunge_all are outside of
* wake_up_process(). There is a race with exit(), see
* ipc/mqueue.c for the details.
*/
#if 0
msg = (struct msg_msg*) msr_d.r_msg;
if(!IS_ERR(msg))
goto out_success;
#endif
while (msg == NULL) {
cpu_relax();
msg = (struct msg_msg*) msr_d.r_msg;
}
msq = msg_lock(msqid);
msg = (struct msg_msg*)msr_d.r_msg;
if(!IS_ERR(msg)) {
/* our message arived while we waited for
* the spinlock. Process it.
*/
if(msq)
msg_unlock(msq);
goto out_success;
/* Lockless receive, part 3:
* If there is a message or an error then accept it without
* locking.
*/
if(msg != ERR_PTR(-EAGAIN)) {
rcu_read_unlock();
break;
}
err = PTR_ERR(msg);
if(err == -EAGAIN) {
if(!msq)
BUG();
list_del(&msr_d.r_list);
if (signal_pending(current))
err=-EINTR;
else
goto retry;
/* Lockless receive, part 3:
* Acquire the queue spinlock.
*/
ipc_lock_by_ptr(&msq->q_perm);
rcu_read_unlock();
/* Lockless receive, part 4:
* Repeat test after acquiring the spinlock.
*/
msg = (struct msg_msg*)msr_d.r_msg;
if(msg != ERR_PTR(-EAGAIN))
goto out_unlock;
list_del(&msr_d.r_list);
if (signal_pending(current)) {
msg = ERR_PTR(-ERESTARTNOHAND);
out_unlock:
msg_unlock(msq);
break;
}
}
out_unlock:
if(msq)
msg_unlock(msq);
return err;
if (IS_ERR(msg))
return PTR_ERR(msg);
msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
if (put_user (msg->m_type, &msgp->mtype) ||
store_msg(msgp->mtext, msg, msgsz)) {
msgsz = -EFAULT;
}
free_msg(msg);
return msgsz;
}
#ifdef CONFIG_PROC_FS
......
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