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minix/kernel/proc.c
Jorrit Herder b16a88692a New deadlock check at proc.c. 
New exit checks (stop IPC).
2005-10-12 15:08:23 +00:00

653 lines
26 KiB
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/* This file contains essentially all of the process and message handling.
* Together with "mpx.s" it forms the lowest layer of the MINIX kernel.
* There is one entry point from the outside:
*
* sys_call: a system call, i.e., the kernel is trapped with an INT
*
* As well as several entry points used from the interrupt and task level:
*
* lock_notify: notify a process of a system event
* lock_send: send a message to a process
* lock_enqueue: put a process on one of the scheduling queues
* lock_dequeue: remove a process from the scheduling queues
*
* Changes:
* Aug 19, 2005 rewrote scheduling code (Jorrit N. Herder)
* Jul 25, 2005 rewrote system call handling (Jorrit N. Herder)
* May 26, 2005 rewrote message passing functions (Jorrit N. Herder)
* May 24, 2005 new notification system call (Jorrit N. Herder)
* Oct 28, 2004 nonblocking send and receive calls (Jorrit N. Herder)
*
* The code here is critical to make everything work and is important for the
* overall performance of the system. A large fraction of the code deals with
* list manipulation. To make this both easy to understand and fast to execute
* pointer pointers are used throughout the code. Pointer pointers prevent
* exceptions for the head or tail of a linked list.
*
* node_t *queue, *new_node; // assume these as global variables
* node_t **xpp = &queue; // get pointer pointer to head of queue
* while (*xpp != NULL) // find last pointer of the linked list
* xpp = &(*xpp)->next; // get pointer to next pointer
* *xpp = new_node; // now replace the end (the NULL pointer)
* new_node->next = NULL; // and mark the new end of the list
*
* For example, when adding a new node to the end of the list, one normally
* makes an exception for an empty list and looks up the end of the list for
* nonempty lists. As shown above, this is not required with pointer pointers.
*/
#include <minix/com.h>
#include <minix/callnr.h>
#include "kernel.h"
#include "proc.h"
/* Scheduling and message passing functions. The functions are available to
* other parts of the kernel through lock_...(). The lock temporarily disables
* interrupts to prevent race conditions.
*/
FORWARD _PROTOTYPE( int mini_send, (struct proc *caller_ptr, int dst,
message *m_ptr, unsigned flags));
FORWARD _PROTOTYPE( int mini_receive, (struct proc *caller_ptr, int src,
message *m_ptr, unsigned flags));
FORWARD _PROTOTYPE( int mini_notify, (struct proc *caller_ptr, int dst));
FORWARD _PROTOTYPE( int deadlock, (int function,
register struct proc *caller, int src_dst));
FORWARD _PROTOTYPE( void enqueue, (struct proc *rp));
FORWARD _PROTOTYPE( void dequeue, (struct proc *rp));
FORWARD _PROTOTYPE( void sched, (struct proc *rp, int *queue, int *front));
FORWARD _PROTOTYPE( void pick_proc, (void));
#define BuildMess(m_ptr, src, dst_ptr) \
(m_ptr)->m_source = (src); \
(m_ptr)->m_type = NOTIFY_FROM(src); \
(m_ptr)->NOTIFY_TIMESTAMP = get_uptime(); \
switch (src) { \
case HARDWARE: \
(m_ptr)->NOTIFY_ARG = priv(dst_ptr)->s_int_pending; \
priv(dst_ptr)->s_int_pending = 0; \
break; \
case SYSTEM: \
(m_ptr)->NOTIFY_ARG = priv(dst_ptr)->s_sig_pending; \
priv(dst_ptr)->s_sig_pending = 0; \
break; \
}
#if (CHIP == INTEL)
#define CopyMess(s,sp,sm,dp,dm) \
cp_mess(s, (sp)->p_memmap[D].mem_phys, \
(vir_bytes)sm, (dp)->p_memmap[D].mem_phys, (vir_bytes)dm)
#endif /* (CHIP == INTEL) */
#if (CHIP == M68000)
/* M68000 does not have cp_mess() in assembly like INTEL. Declare prototype
* for cp_mess() here and define the function below. Also define CopyMess.
*/
#endif /* (CHIP == M68000) */
/*===========================================================================*
* sys_call *
*===========================================================================*/
PUBLIC int sys_call(call_nr, src_dst, m_ptr)
int call_nr; /* system call number and flags */
int src_dst; /* src to receive from or dst to send to */
message *m_ptr; /* pointer to message in the caller's space */
{
/* System calls are done by trapping to the kernel with an INT instruction.
* The trap is caught and sys_call() is called to send or receive a message
* (or both). The caller is always given by 'proc_ptr'.
*/
register struct proc *caller_ptr = proc_ptr; /* get pointer to caller */
int function = call_nr & SYSCALL_FUNC; /* get system call function */
unsigned flags = call_nr & SYSCALL_FLAGS; /* get flags */
int mask_entry; /* bit to check in send mask */
int group_size; /* used for deadlock check */
int result; /* the system call's result */
vir_clicks vlo, vhi; /* virtual clicks containing message to send */
/* Check if the process has privileges for the requested call. Calls to the
* kernel may only be SENDREC, because tasks always reply and may not block
* if the caller doesn't do receive().
*/
if (! (priv(caller_ptr)->s_trap_mask & (1 << function)) ||
(iskerneln(src_dst) && function != SENDREC
&& function != RECEIVE)) {
kprintf("sys_call: trap %d not allowed, caller %d, src_dst %d\n",
function, proc_nr(caller_ptr), src_dst);
return(ECALLDENIED); /* trap denied by mask or kernel */
}
/* Require a valid source and/ or destination process, unless echoing. */
if (src_dst != ANY && function != ECHO) {
if (! isokprocn(src_dst)) {
kprintf("sys_call: invalid src_dst, src_dst %d, caller %d\n",
src_dst, proc_nr(caller_ptr));
return(EBADSRCDST); /* invalid process number */
}
if (isemptyn(src_dst)) {
kprintf("sys_call: dead src_dst; trap %d, from %d, to %d\n",
function, proc_nr(caller_ptr), src_dst);
return(EDEADSRCDST);
}
}
/* If the call involves a message buffer, i.e., for SEND, RECEIVE, SENDREC,
* or ECHO, check the message pointer. This check allows a message to be
* anywhere in data or stack or gap. It will have to be made more elaborate
* for machines which don't have the gap mapped.
*/
if (function & CHECK_PTR) {
vlo = (vir_bytes) m_ptr >> CLICK_SHIFT;
vhi = ((vir_bytes) m_ptr + MESS_SIZE - 1) >> CLICK_SHIFT;
if (vlo < caller_ptr->p_memmap[D].mem_vir || vlo > vhi ||
vhi >= caller_ptr->p_memmap[S].mem_vir +
caller_ptr->p_memmap[S].mem_len) {
kprintf("sys_call: invalid message pointer, trap %d, caller %d\n",
function, proc_nr(caller_ptr));
return(EFAULT); /* invalid message pointer */
}
}
/* If the call is to send to a process, i.e., for SEND, SENDREC or NOTIFY,
* verify that the caller is allowed to send to the given destination.
*/
if (function & CHECK_DST) {
if (! get_sys_bit(priv(caller_ptr)->s_ipc_to, nr_to_id(src_dst))) {
kprintf("sys_call: ipc mask denied trap %d from %d to %d\n",
function, proc_nr(caller_ptr), src_dst);
return(ECALLDENIED); /* call denied by ipc mask */
}
}
/* Check for a possible deadlock for blocking SEND(REC) and RECEIVE. */
if (function & CHECK_DEADLOCK) {
if (group_size = deadlock(function, caller_ptr, src_dst)) {
kprintf("sys_call: trap %d from %d to %d deadlocked, group size %d\n",
function, proc_nr(caller_ptr), src_dst, group_size);
return(ELOCKED);
}
}
/* Now check if the call is known and try to perform the request. The only
* system calls that exist in MINIX are sending and receiving messages.
* - SENDREC: combines SEND and RECEIVE in a single system call
* - SEND: sender blocks until its message has been delivered
* - RECEIVE: receiver blocks until an acceptable message has arrived
* - NOTIFY: nonblocking call; deliver notification or mark pending
* - ECHO: nonblocking call; directly echo back the message
*/
switch(function) {
case SENDREC:
/* A flag is set so that notifications cannot interrupt SENDREC. */
priv(caller_ptr)->s_flags |= SENDREC_BUSY;
/* fall through */
case SEND:
result = mini_send(caller_ptr, src_dst, m_ptr, flags);
if (function == SEND || result != OK) {
break; /* done, or SEND failed */
} /* fall through for SENDREC */
case RECEIVE:
if (function == RECEIVE)
priv(caller_ptr)->s_flags &= ~SENDREC_BUSY;
result = mini_receive(caller_ptr, src_dst, m_ptr, flags);
break;
case NOTIFY:
result = mini_notify(caller_ptr, src_dst);
break;
case ECHO:
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, caller_ptr, m_ptr);
result = OK;
break;
default:
result = EBADCALL; /* illegal system call */
}
/* Now, return the result of the system call to the caller. */
return(result);
}
/*===========================================================================*
* deadlock *
*===========================================================================*/
PRIVATE int deadlock(function, cp, src_dst)
int function; /* trap number */
register struct proc *cp; /* pointer to caller */
register int src_dst; /* src or dst process */
{
/* Check for deadlock. This can happen if 'caller_ptr' and 'src_dst' have
* a cyclic dependency of blocking send and receive calls. The only cyclic
* depency that is not fatal is if the caller and target directly SEND(REC)
* and RECEIVE to each other. If a deadlock is found, the group size is
* returned. Otherwise zero is returned.
*/
register struct proc *xp; /* process pointer */
int group_size = 1; /* start with only caller */
int trap_flags;
while (src_dst != ANY) { /* check while process nr */
xp = proc_addr(src_dst); /* follow chain of processes */
group_size ++; /* extra process in group */
/* Check whether the last process in the chain has a depency. If it
* has not, the cycle cannot be closed and we are done.
*/
if (xp->p_rts_flags & RECEIVING) { /* xp has dependency */
src_dst = xp->p_getfrom; /* get xp's source */
} else if (xp->p_rts_flags & SENDING) { /* xp has dependency */
src_dst = xp->p_sendto; /* get xp's destination */
} else {
return(0); /* not a deadlock */
}
/* Now check if there is a cyclic dependency. For group sizes of two,
* a combination of SEND(REC) and RECEIVE is not fatal. Larger groups
* or other combinations indicate a deadlock.
*/
if (src_dst == proc_nr(cp)) { /* possible deadlock */
if (group_size == 2) { /* caller and src_dst */
/* The function number is magically converted to flags. */
if ((xp->p_rts_flags ^ (function << 2)) & SENDING) {
return(0); /* not a deadlock */
}
}
return(group_size); /* deadlock found */
}
}
return(0); /* not a deadlock */
}
/*===========================================================================*
* mini_send *
*===========================================================================*/
PRIVATE int mini_send(caller_ptr, dst, m_ptr, flags)
register struct proc *caller_ptr; /* who is trying to send a message? */
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* Send a message from 'caller_ptr' to 'dst'. If 'dst' is blocked waiting
* for this message, copy the message to it and unblock 'dst'. If 'dst' is
* not waiting at all, or is waiting for another source, queue 'caller_ptr'.
*/
register struct proc *dst_ptr = proc_addr(dst);
register struct proc **xpp;
/* Check if 'dst' is blocked waiting for this message. The destination's
* SENDING flag may be set when its SENDREC call blocked while sending.
*/
if ( (dst_ptr->p_rts_flags & (RECEIVING | SENDING)) == RECEIVING &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for this message. */
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, dst_ptr,
dst_ptr->p_messbuf);
if ((dst_ptr->p_rts_flags &= ~RECEIVING) == 0) enqueue(dst_ptr);
} else if ( ! (flags & NON_BLOCKING)) {
/* Destination is not waiting. Block and dequeue caller. */
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_rts_flags == 0) dequeue(caller_ptr);
caller_ptr->p_rts_flags |= SENDING;
caller_ptr->p_sendto = dst;
/* Process is now blocked. Put in on the destination's queue. */
xpp = &dst_ptr->p_caller_q; /* find end of list */
while (*xpp != NIL_PROC) xpp = &(*xpp)->p_q_link;
*xpp = caller_ptr; /* add caller to end */
caller_ptr->p_q_link = NIL_PROC; /* mark new end of list */
} else {
return(ENOTREADY);
}
return(OK);
}
/*===========================================================================*
* mini_receive *
*===========================================================================*/
PRIVATE int mini_receive(caller_ptr, src, m_ptr, flags)
register struct proc *caller_ptr; /* process trying to get message */
int src; /* which message source is wanted */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* A process or task wants to get a message. If a message is already queued,
* acquire it and deblock the sender. If no message from the desired source
* is available block the caller, unless the flags don't allow blocking.
*/
register struct proc **xpp;
register struct notification **ntf_q_pp;
message m;
int bit_nr;
sys_map_t *map;
bitchunk_t *chunk;
int i, src_id, src_proc_nr;
/* Check to see if a message from desired source is already available.
* The caller's SENDING flag may be set if SENDREC couldn't send. If it is
* set, the process should be blocked.
*/
if (!(caller_ptr->p_rts_flags & SENDING)) {
/* Check if there are pending notifications, except for SENDREC. */
if (! (priv(caller_ptr)->s_flags & SENDREC_BUSY)) {
map = &priv(caller_ptr)->s_notify_pending;
for (chunk=&map->chunk[0]; chunk<&map->chunk[NR_SYS_CHUNKS]; chunk++) {
/* Find a pending notification from the requested source. */
if (! *chunk) continue; /* no bits in chunk */
for (i=0; ! (*chunk & (1<<i)); ++i) {} /* look up the bit */
src_id = (chunk - &map->chunk[0]) * BITCHUNK_BITS + i;
if (src_id >= NR_SYS_PROCS) break; /* out of range */
src_proc_nr = id_to_nr(src_id); /* get source proc */
if (src!=ANY && src!=src_proc_nr) continue; /* source not ok */
*chunk &= ~(1 << i); /* no longer pending */
/* Found a suitable source, deliver the notification message. */
BuildMess(&m, src_proc_nr, caller_ptr); /* assemble message */
CopyMess(src_proc_nr, proc_addr(HARDWARE), &m, caller_ptr, m_ptr);
return(OK); /* report success */
}
}
/* Check caller queue. Use pointer pointers to keep code simple. */
xpp = &caller_ptr->p_caller_q;
while (*xpp != NIL_PROC) {
if (src == ANY || src == proc_nr(*xpp)) {
/* Found acceptable message. Copy it and update status. */
CopyMess((*xpp)->p_nr, *xpp, (*xpp)->p_messbuf, caller_ptr, m_ptr);
if (((*xpp)->p_rts_flags &= ~SENDING) == 0) enqueue(*xpp);
*xpp = (*xpp)->p_q_link; /* remove from queue */
return(OK); /* report success */
}
xpp = &(*xpp)->p_q_link; /* proceed to next */
}
}
/* No suitable message is available or the caller couldn't send in SENDREC.
* Block the process trying to receive, unless the flags tell otherwise.
*/
if ( ! (flags & NON_BLOCKING)) {
caller_ptr->p_getfrom = src;
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_rts_flags == 0) dequeue(caller_ptr);
caller_ptr->p_rts_flags |= RECEIVING;
return(OK);
} else {
return(ENOTREADY);
}
}
/*===========================================================================*
* mini_notify *
*===========================================================================*/
PRIVATE int mini_notify(caller_ptr, dst)
register struct proc *caller_ptr; /* sender of the notification */
int dst; /* which process to notify */
{
register struct proc *dst_ptr = proc_addr(dst);
int src_id; /* source id for late delivery */
message m; /* the notification message */
/* Check to see if target is blocked waiting for this message. A process
* can be both sending and receiving during a SENDREC system call.
*/
if ((dst_ptr->p_rts_flags & (RECEIVING|SENDING)) == RECEIVING &&
! (priv(dst_ptr)->s_flags & SENDREC_BUSY) &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for a message. Assemble a notification
* message and deliver it. Copy from pseudo-source HARDWARE, since the
* message is in the kernel's address space.
*/
BuildMess(&m, proc_nr(caller_ptr), dst_ptr);
CopyMess(proc_nr(caller_ptr), proc_addr(HARDWARE), &m,
dst_ptr, dst_ptr->p_messbuf);
dst_ptr->p_rts_flags &= ~RECEIVING; /* deblock destination */
if (dst_ptr->p_rts_flags == 0) enqueue(dst_ptr);
return(OK);
}
/* Destination is not ready to receive the notification. Add it to the
* bit map with pending notifications. Note the indirectness: the system id
* instead of the process number is used in the pending bit map.
*/
src_id = priv(caller_ptr)->s_id;
set_sys_bit(priv(dst_ptr)->s_notify_pending, src_id);
return(OK);
}
/*===========================================================================*
* lock_notify *
*===========================================================================*/
PUBLIC int lock_notify(src, dst)
int src; /* sender of the notification */
int dst; /* who is to be notified */
{
/* Safe gateway to mini_notify() for tasks and interrupt handlers. The sender
* is explicitely given to prevent confusion where the call comes from. MINIX
* kernel is not reentrant, which means to interrupts are disabled after
* the first kernel entry (hardware interrupt, trap, or exception). Locking
* is done by temporarily disabling interrupts.
*/
int result;
/* Exception or interrupt occurred, thus already locked. */
if (k_reenter >= 0) {
result = mini_notify(proc_addr(src), dst);
}
/* Call from task level, locking is required. */
else {
lock(0, "notify");
result = mini_notify(proc_addr(src), dst);
unlock(0);
}
return(result);
}
/*===========================================================================*
* enqueue *
*===========================================================================*/
PRIVATE void enqueue(rp)
register struct proc *rp; /* this process is now runnable */
{
/* Add 'rp' to one of the queues of runnable processes. This function is
* responsible for inserting a process into one of the scheduling queues.
* The mechanism is implemented here. The actual scheduling policy is
* defined in sched() and pick_proc().
*/
int q; /* scheduling queue to use */
int front; /* add to front or back */
#if DEBUG_SCHED_CHECK
check_runqueues("enqueue");
if (rp->p_ready) kprintf("enqueue() already ready process\n");
#endif
/* Determine where to insert to process. */
sched(rp, &q, &front);
/* Now add the process to the queue. */
if (rdy_head[q] == NIL_PROC) { /* add to empty queue */
rdy_head[q] = rdy_tail[q] = rp; /* create a new queue */
rp->p_nextready = NIL_PROC; /* mark new end */
}
else if (front) { /* add to head of queue */
rp->p_nextready = rdy_head[q]; /* chain head of queue */
rdy_head[q] = rp; /* set new queue head */
}
else { /* add to tail of queue */
rdy_tail[q]->p_nextready = rp; /* chain tail of queue */
rdy_tail[q] = rp; /* set new queue tail */
rp->p_nextready = NIL_PROC; /* mark new end */
}
/* Now select the next process to run. */
pick_proc();
#if DEBUG_SCHED_CHECK
rp->p_ready = 1;
check_runqueues("enqueue");
#endif
}
/*===========================================================================*
* dequeue *
*===========================================================================*/
PRIVATE void dequeue(rp)
register struct proc *rp; /* this process is no longer runnable */
{
/* A process must be removed from the scheduling queues, for example, because
* it has blocked. If the currently active process is removed, a new process
* is picked to run by calling pick_proc().
*/
register int q = rp->p_priority; /* queue to use */
register struct proc **xpp; /* iterate over queue */
register struct proc *prev_xp;
/* Side-effect for kernel: check if the task's stack still is ok? */
if (iskernelp(rp)) {
if (*priv(rp)->s_stack_guard != STACK_GUARD)
panic("stack overrun by task", proc_nr(rp));
}
#if DEBUG_SCHED_CHECK
check_runqueues("dequeue");
if (! rp->p_ready) kprintf("dequeue() already unready process\n");
#endif
/* Now make sure that the process is not in its ready queue. Remove the
* process if it is found. A process can be made unready even if it is not
* running by being sent a signal that kills it.
*/
prev_xp = NIL_PROC;
for (xpp = &rdy_head[q]; *xpp != NIL_PROC; xpp = &(*xpp)->p_nextready) {
if (*xpp == rp) { /* found process to remove */
*xpp = (*xpp)->p_nextready; /* replace with next chain */
if (rp == rdy_tail[q]) /* queue tail removed */
rdy_tail[q] = prev_xp; /* set new tail */
if (rp == proc_ptr || rp == next_ptr) /* active process removed */
pick_proc(); /* pick new process to run */
break;
}
prev_xp = *xpp; /* save previous in chain */
}
#if DEBUG_SCHED_CHECK
rp->p_ready = 0;
check_runqueues("dequeue");
#endif
}
/*===========================================================================*
* sched *
*===========================================================================*/
PRIVATE void sched(rp, queue, front)
register struct proc *rp; /* process to be scheduled */
int *queue; /* return: queue to use */
int *front; /* return: front or back */
{
/* This function determines the scheduling policy. It is called whenever a
* process must be added to one of the scheduling queues to decide where to
* insert it. As a side-effect the process' priority may be updated.
*/
static struct proc *prev_ptr = NIL_PROC; /* previous without time */
int time_left = (rp->p_ticks_left > 0); /* quantum fully consumed */
int penalty = 0; /* change in priority */
/* Check whether the process has time left. Otherwise give a new quantum
* and possibly raise the priority. Processes using multiple quantums
* in a row get a lower priority to catch infinite loops in high priority
* processes (system servers and drivers).
*/
if ( ! time_left) { /* quantum consumed ? */
rp->p_ticks_left = rp->p_quantum_size; /* give new quantum */
if (prev_ptr == rp) penalty ++; /* catch infinite loops */
else penalty --; /* give slow way back */
prev_ptr = rp; /* store ptr for next */
}
/* Determine the new priority of this process. The bounds are determined
* by IDLE's queue and the maximum priority of this process. Kernel task
* and the idle process are never changed in priority.
*/
if (penalty != 0 && ! iskernelp(rp)) {
rp->p_priority += penalty; /* update with penalty */
if (rp->p_priority < rp->p_max_priority) /* check upper bound */
rp->p_priority=rp->p_max_priority;
else if (rp->p_priority > IDLE_Q-1) /* check lower bound */
rp->p_priority = IDLE_Q-1;
}
/* If there is time left, the process is added to the front of its queue,
* so that it can immediately run. The queue to use simply is always the
* process' current priority.
*/
*queue = rp->p_priority;
*front = time_left;
}
/*===========================================================================*
* pick_proc *
*===========================================================================*/
PRIVATE void pick_proc()
{
/* Decide who to run now. A new process is selected by setting 'next_ptr'.
* When a billable process is selected, record it in 'bill_ptr', so that the
* clock task can tell who to bill for system time.
*/
register struct proc *rp; /* process to run */
int q; /* iterate over queues */
/* Check each of the scheduling queues for ready processes. The number of
* queues is defined in proc.h, and priorities are set in the task table.
* The lowest queue contains IDLE, which is always ready.
*/
for (q=0; q < NR_SCHED_QUEUES; q++) {
if ( (rp = rdy_head[q]) != NIL_PROC) {
next_ptr = rp; /* run process 'rp' next */
if (priv(rp)->s_flags & BILLABLE)
bill_ptr = rp; /* bill for system time */
return;
}
}
}
/*===========================================================================*
* lock_send *
*===========================================================================*/
PUBLIC int lock_send(dst, m_ptr)
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
{
/* Safe gateway to mini_send() for tasks. */
int result;
lock(2, "send");
result = mini_send(proc_ptr, dst, m_ptr, NON_BLOCKING);
unlock(2);
return(result);
}
/*===========================================================================*
* lock_enqueue *
*===========================================================================*/
PUBLIC void lock_enqueue(rp)
struct proc *rp; /* this process is now runnable */
{
/* Safe gateway to enqueue() for tasks. */
lock(3, "enqueue");
enqueue(rp);
unlock(3);
}
/*===========================================================================*
* lock_dequeue *
*===========================================================================*/
PUBLIC void lock_dequeue(rp)
struct proc *rp; /* this process is no longer runnable */
{
/* Safe gateway to dequeue() for tasks. */
lock(4, "dequeue");
dequeue(rp);
unlock(4);
}
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