From aeaa308943a14acfaab00f0d9af8424d21a991ae Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Thu, 15 Sep 2016 12:12:05 -0400
Subject: change allocproc() back to acquiring the ptable.lock. fix bugs where
caller incorrectly released lock on error return path.
---
proc.c | 20 ++++++--------------
1 file changed, 6 insertions(+), 14 deletions(-)
diff --git a/proc.c b/proc.c
index eee79af..7d03ad7 100644
--- a/proc.c
+++ b/proc.c
@@ -31,22 +31,27 @@ pinit(void)
// If found, change state to EMBRYO and initialize
// state required to run in the kernel.
// Otherwise return 0.
-// Must hold ptable.lock.
static struct proc*
allocproc(void)
{
struct proc *p;
char *sp;
+ acquire(&ptable.lock);
+
for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
if(p->state == UNUSED)
goto found;
+
+ release(&ptable.lock);
return 0;
found:
p->state = EMBRYO;
p->pid = nextpid++;
+ release(&ptable.lock);
+
// Allocate kernel stack.
if((p->kstack = kalloc()) == 0){
p->state = UNUSED;
@@ -79,14 +84,7 @@ userinit(void)
struct proc *p;
extern char _binary_initcode_start[], _binary_initcode_size[];
- acquire(&ptable.lock);
-
p = allocproc();
-
- // release the lock in case namei() sleeps.
- // the lock isn't needed because no other
- // thread will look at an EMBRYO proc.
- release(&ptable.lock);
initproc = p;
if((p->pgdir = setupkvm()) == 0)
@@ -145,22 +143,16 @@ fork(void)
int i, pid;
struct proc *np;
- acquire(&ptable.lock);
-
// Allocate process.
if((np = allocproc()) == 0){
- release(&ptable.lock);
return -1;
}
- release(&ptable.lock);
-
// Copy process state from p.
if((np->pgdir = copyuvm(proc->pgdir, proc->sz)) == 0){
kfree(np->kstack);
np->kstack = 0;
np->state = UNUSED;
- release(&ptable.lock);
return -1;
}
np->sz = proc->sz;
--
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