diff options
| -rw-r--r-- | kernel/proc.c | 49 | ||||
| -rw-r--r-- | kernel/syscall.c | 16 | ||||
| -rw-r--r-- | kernel/trap.c | 3 |
3 files changed, 32 insertions, 36 deletions
diff --git a/kernel/proc.c b/kernel/proc.c index 5c2d4ce..1c222d3 100644 --- a/kernel/proc.c +++ b/kernel/proc.c @@ -367,19 +367,24 @@ wait(void) // Scan through table looking for exited children. havekids = 0; for(np = proc; np < &proc[NPROC]; np++){ - if(np->parent != p) - continue; - acquire(&np->lock); - havekids = 1; - if(np->state == ZOMBIE){ - // Found one. - pid = np->pid; - freeproc(np); + // this code uses np->parent without holding np->lock. + // acquiring the lock first would cause a deadlock, + // since np might be an ancestor, and we already hold p->lock. + if(np->parent == p){ + // np->parent can't change here because only the parent + // changes it, and we're the parent. + acquire(&np->lock); + havekids = 1; + if(np->state == ZOMBIE){ + // Found one. + pid = np->pid; + freeproc(np); + release(&np->lock); + release(&p->lock); + return pid; + } release(&np->lock); - release(&p->lock); - return pid; } - release(&np->lock); } // No point waiting if we don't have any children. @@ -397,10 +402,10 @@ wait(void) // Per-CPU process scheduler. // Each CPU calls scheduler() after setting itself up. // Scheduler never returns. It loops, doing: -// - choose a process to run -// - swtch to start running that process +// - choose a process to run. +// - swtch to start running that process. // - eventually that process transfers control -// via swtch back to the scheduler. +// via swtch back to the scheduler. void scheduler(void) { @@ -409,7 +414,7 @@ scheduler(void) c->proc = 0; for(;;){ - // Enable interrupts on this processor. + // Give devices a brief chance to interrupt. intr_on(); for(p = proc; p < &proc[NPROC]; p++) { @@ -508,7 +513,7 @@ sleep(void *chan, struct spinlock *lk) // change p->state and then call sched. // Once we hold p->lock, we can be // guaranteed that we won't miss any wakeup - // (wakeup runs with p->lock locked), + // (wakeup locks p->lock), // so it's okay to release lk. if(lk != &p->lock){ //DOC: sleeplock0 acquire(&p->lock); //DOC: sleeplock1 @@ -559,24 +564,24 @@ wakeup(void *chan) // Kill the process with the given pid. // Process won't exit until it returns -// to user space (see trap in trap.c). +// to user space (see usertrap() in trap.c). int kill(int pid) { struct proc *p; for(p = proc; p < &proc[NPROC]; p++){ + acquire(&p->lock); if(p->pid == pid){ - acquire(&p->lock); - if(p->pid != pid) - panic("kill"); p->killed = 1; - // Wake process from sleep if necessary. - if(p->state == SLEEPING) + if(p->state == SLEEPING){ + // Wake process from sleep(). p->state = RUNNABLE; + } release(&p->lock); return 0; } + release(&p->lock); } return -1; } diff --git a/kernel/syscall.c b/kernel/syscall.c index a054da2..adbad73 100644 --- a/kernel/syscall.c +++ b/kernel/syscall.c @@ -163,8 +163,8 @@ static uint64 (*syscalls[])(void) = { [SYS_close] sys_close, }; -static void -dosyscall(void) +void +syscall(void) { int num; struct proc *p = myproc(); @@ -180,15 +180,3 @@ dosyscall(void) p->tf->a0 = -1; } } - -void -syscall() -{ - if(myproc()->killed) - exit(); - dosyscall(); - if(myproc()->killed) - exit(); - return; -} - diff --git a/kernel/trap.c b/kernel/trap.c index 27cfd32..eb7f6cf 100644 --- a/kernel/trap.c +++ b/kernel/trap.c @@ -53,6 +53,9 @@ usertrap(void) if(r_scause() == 8){ // system call + if(p->killed) + exit(); + // sepc points to the ecall instruction, // but we want to return to the next instruction. p->tf->epc += 4; |