PROBLEM:a bug about pi-futex maybe let the program going to hang

scxby
2011-03-26T04:41:46Z

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="gb2312", Size: 1381 bytes --]

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.ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éÝ¶\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dÊ‡Ú™ë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥