Messages in this thread | | | Date | Wed, 10 Jun 2009 23:21:19 -0700 | From | Darren Hart <> | Subject | Re: Bug: fio traps into kernel without exiting because futex has a deadloop |
| |
Peter Zijlstra wrote: > On Thu, 2009-06-11 at 07:55 +0200, Peter Zijlstra wrote: >> On Thu, 2009-06-11 at 11:08 +0800, Zhang, Yanmin wrote: >>> I investigate a fio hang issue. When I run fio multi-process >>> testing on many disks, fio traps into kernel and doesn't exit >>> (mostly hit once after runing sub test cases for hundreds of times). >>> >>> Oprofile data shows kernel consumes time with some futex functions. >>> Command kill couldn't kill the process and machine reboot also hangs. >>> >>> Eventually, I locate the root cause as a bug of futex. Kernel enters >>> a deadloop between 'retry' and 'goto retry' in function futex_wake_op. >>> By unknown reason (might be an issue of fio or glibc), parameter uaddr2 >>> points to an area which is READONLY. So futex_atomic_op_inuser returns >>> -EFAULT when trying to changing the data at uaddr2, but later get_user >>> still succeeds becasue the area is READONLY. Then go back to retry. >>> >>> I create a simple test case to trigger it, which just shmat an READONLY >>> area for address uaddr2. >>> >>> It could be used as a DOS attack. > > /me has morning juice and notices he sent the wrong commit... > > commit 64d1304a64477629cb16b75491a77bafe6f86963 > Author: Thomas Gleixner <tglx@linutronix.de> > Date: Mon May 18 21:20:10 2009 +0200 > > futex: setup writeable mapping for futex ops which modify user space data
Yup, that's the one. I was trying to locate it myself, but you beat me to it. Thanks Peter.
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team -- 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/
| |