Messages in this thread | | | From | "scxby" <> | Subject | PROBLEM:a bug about pi-futex maybe let the program going to hang | Date | Sat, 26 Mar 2011 12:19:03 +0800 |
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hi, all.
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. | |