Messages in this thread | | | Subject | Re: PROBLEM:a bug about pi-futex maybe let the program going to hang | From | Peter Zijlstra <> | Date | Mon, 28 Mar 2011 10:26:22 +0200 |
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On Mon, 2011-03-28 at 15:25 +0800, xby wrote: > hi, all.
Works better if you also CC people who actually work on that code.
> Maybe, there is a bug about pi-futex, it would let the program in user-space going to hang. > > We have a board: CPU is powerpc 8572, two core. after ran one month, the state of pi-futex in user-space got bad: mutex->__data.__lock is 0x8000023e, mutex->__data.__count is 0, mutex->__data.__owner is 0. > > then, I review file "kernel/funtex.c"(the version is linux 2.6.38), found a case: > > if there are 3 thread, named threadA, threadB, threadC。thread A hold mutexM, threadB and threadC is waiting mutexM. They run as fllow steps: > > 1. threadB and threadC sleep at line 1984. > 2. threadB receive a signal, then it will be wake up. > 3. threadA unlock mutexM, and give mutexM to threadB. > 4. threadB call fixup_owner, try to give mutex to threadC. > 5. at line 1580, threadB trigger a addr-fault, then goto handle_fault. > 6. at line 1617, threadB release spinlock, then handle fault. > 7. threadC got spinlock, and call fixup_owner, and got mutexM. > 8. threadC give mutexM to threadB. > 9. threadB re-got spinlock, it will found "pi_state->owner == oldowner" and retry to fixup. > 10. threadB give mutexM to threadC, that's a bad thing. > > we have wrote a program, this program can prove all above.
It would have been ever so much more useful if you'd have included that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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