Imbus/xv6-riscv-kernel
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fix an exit/exit deadlock -> one more locking protocol violation

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increase timer rate from 1/second to 10/second
This commit is contained in:
Robert Morris 2019-07-25 06:30:49 -04:00
parent b19adf79f9
commit 4e62de64cd
3 changed files with 22 additions and 17 deletions
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24
kernel/proc.c
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@ -294,17 +294,21 @@ reparent(struct proc *p, struct proc *parent) {
int child_of_init = (p->parent == initproc);
for(pp = proc; pp < &proc[NPROC]; pp++){
if (pp != p && pp != parent) {
// this code uses pp->parent without holding pp->lock.
// acquiring the lock first could cause a deadlock
// if pp or a child of pp were also in exit()
// and about to try to lock p.
if(pp->parent == p){
// pp->parent can't change between the check and the acquire()
// because only the parent changes it, and we're the parent.
acquire(&pp->lock);
if(pp->parent == p){
pp->parent = initproc;
if(pp->state == ZOMBIE) {
if(!child_of_init)
acquire(&initproc->lock);
wakeup1(initproc);
if(!child_of_init)
release(&initproc->lock);
}
pp->parent = initproc;
if(pp->state == ZOMBIE) {
if(!child_of_init)
acquire(&initproc->lock);
wakeup1(initproc);
if(!child_of_init)
release(&initproc->lock);
}
release(&pp->lock);
}

9
kernel/start.c
View file

@ -41,15 +41,16 @@ start()
// which turns them into software interrupts for
// devintr() in trap.c.
int id = r_mhartid();
// ask the CLINT for a timer interrupt 10,000 cycles from now.
*(uint64*)CLINT_MTIMECMP(id) = *(uint64*)CLINT_MTIME + 10000;
// ask the CLINT for a timer interrupt.
int interval = 1000000; // cycles; about 1/10th second in qemu.
*(uint64*)CLINT_MTIMECMP(id) = *(uint64*)CLINT_MTIME + interval;
// prepare information in scratch[] for machinevec.
// scratch[0..3] : space for machinevec to save registers.
// scratch[4] : address of CLINT MTIMECMP register.
// scratch[5] : desired interval (in cycles) between timer interrupts.
uint64 *scratch = &mscratch0[32 * id];
scratch[4] = CLINT_MTIMECMP(id);
scratch[5] = 10000000;
scratch[5] = interval;
w_mscratch((uint64)scratch);
// set the machine-mode trap handler.
w_mtvec((uint64)machinevec);
@ -61,6 +62,6 @@ start()
// keep each CPU's hartid in its tp register, for cpuid().
w_tp(id);
// call main() in supervisor mode.
// switch to supervisor mode and jump to main().
asm volatile("mret");
}