70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
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#include <inc/lib.h>
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void
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umain(int argc, char **argv)
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{
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int p[2], r, i;
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struct Fd *fd;
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const volatile struct Env *kid;
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cprintf("testing for pipeisclosed race...\n");
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if ((r = pipe(p)) < 0)
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panic("pipe: %e", r);
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if ((r = fork()) < 0)
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panic("fork: %e", r);
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if (r == 0) {
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// child just dups and closes repeatedly,
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// yielding so the parent can see
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// the fd state between the two.
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close(p[1]);
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for (i = 0; i < 200; i++) {
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if (i % 10 == 0)
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cprintf("%d.", i);
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// dup, then close. yield so that other guy will
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// see us while we're between them.
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dup(p[0], 10);
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sys_yield();
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close(10);
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sys_yield();
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}
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exit();
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}
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// We hold both p[0] and p[1] open, so pipeisclosed should
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// never return false.
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//
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// Now the ref count for p[0] will toggle between 2 and 3
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// as the child dups and closes it.
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// The ref count for p[1] is 1.
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// Thus the ref count for the underlying pipe structure
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// will toggle between 3 and 4.
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//
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// If pipeisclosed checks pageref(p[0]) and gets 3, and
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// then the child closes, and then pipeisclosed checks
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// pageref(pipe structure) and gets 3, then it will return true
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// when it shouldn't.
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//
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// If pipeisclosed checks pageref(pipe structure) and gets 3,
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// and then the child dups, and then pipeisclosed checks
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// pageref(p[0]) and gets 3, then it will return true when
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// it shouldn't.
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//
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// So either way, pipeisclosed is going give a wrong answer.
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//
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kid = &envs[ENVX(r)];
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while (kid->env_status == ENV_RUNNABLE)
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if (pipeisclosed(p[0]) != 0) {
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cprintf("\nRACE: pipe appears closed\n");
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sys_env_destroy(r);
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exit();
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}
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cprintf("child done with loop\n");
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if (pipeisclosed(p[0]))
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panic("somehow the other end of p[0] got closed!");
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if ((r = fd_lookup(p[0], &fd)) < 0)
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panic("cannot look up p[0]: %e", r);
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(void) fd2data(fd);
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cprintf("race didn't happen\n");
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}
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