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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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10
kernel/proc.c
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@ -294,9 +294,14 @@ reparent(struct proc *p, struct proc *parent) {
int child_of_init = (p->parent == initproc); int child_of_init = (p->parent == initproc);
for(pp = proc; pp < &proc[NPROC]; pp++){ for(pp = proc; pp < &proc[NPROC]; pp++){
if (pp != p && pp != parent) { // this code uses pp->parent without holding pp->lock.
acquire(&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){ 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);
pp->parent = initproc; pp->parent = initproc;
if(pp->state == ZOMBIE) { if(pp->state == ZOMBIE) {
if(!child_of_init) if(!child_of_init)
@ -305,7 +310,6 @@ reparent(struct proc *p, struct proc *parent) {
if(!child_of_init) if(!child_of_init)
release(&initproc->lock); release(&initproc->lock);
} }
}
release(&pp->lock); release(&pp->lock);
} }
} }

9
kernel/start.c
View file

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

6
user/usertests.c
View file

@ -448,7 +448,7 @@ reparent(void)
printf(1, "reparent test\n"); printf(1, "reparent test\n");
for(int i = 0; i < 100; i++){ for(int i = 0; i < 200; i++){
int pid = fork(); int pid = fork();
if(pid < 0){ if(pid < 0){
printf(1, "fork failed\n"); printf(1, "fork failed\n");
@ -571,10 +571,10 @@ forkforkfork(void)
exit(); exit();
} }
sleep(2); sleep(20); // two seconds
close(open("stopforking", O_CREATE|O_RDWR)); close(open("stopforking", O_CREATE|O_RDWR));
wait(); wait();
sleep(1); sleep(10); // one second
printf(1, "forkforkfork ok\n"); printf(1, "forkforkfork ok\n");
} }