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try to handle a few of the possible out-of-memory errors in fork()

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Robert Morris 2020-08-13 09:19:23 -04:00
parent 70c6fe861e
commit 4c22c54480
1 changed files with 18 additions and 5 deletions
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23
kernel/proc.c
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@ -17,6 +17,7 @@ struct spinlock pid_lock;
extern void forkret(void);
static void wakeup1(struct proc *chan);
static void freeproc(struct proc *p);
extern char trampoline[]; // trampoline.S
@ -87,7 +88,7 @@ allocpid() {
// Look in the process table for an UNUSED proc.
// If found, initialize state required to run in the kernel,
// and return with p->lock held.
// If there are no free procs, return 0.
// If there are no free procs, or a memory allocation fails, return 0.
static struct proc*
allocproc(void)
{
@ -114,6 +115,11 @@ found:
// An empty user page table.
p->pagetable = proc_pagetable(p);
if(p->pagetable == 0){
freeproc(p);
release(&p->lock);
return 0;
}
// Set up new context to start executing at forkret,
// which returns to user space.
@ -160,12 +166,19 @@ proc_pagetable(struct proc *p)
// at the highest user virtual address.
// only the supervisor uses it, on the way
// to/from user space, so not PTE_U.
mappages(pagetable, TRAMPOLINE, PGSIZE,
(uint64)trampoline, PTE_R | PTE_X);
if(mappages(pagetable, TRAMPOLINE, PGSIZE,
(uint64)trampoline, PTE_R | PTE_X) < 0){
uvmfree(pagetable, 0);
return 0;
}
// map the trapframe just below TRAMPOLINE, for trampoline.S.
mappages(pagetable, TRAPFRAME, PGSIZE,
(uint64)(p->trapframe), PTE_R | PTE_W);
if(mappages(pagetable, TRAPFRAME, PGSIZE,
(uint64)(p->trapframe), PTE_R | PTE_W) < 0){
uvmunmap(pagetable, TRAMPOLINE, 1, 0);
uvmfree(pagetable, 0);
return 0;
}
return pagetable;
}