Messages in this thread Patch in this message | | | From | Frank Seidel <> | Subject | Re: PROBLEM: null pointer dereference in cfq_dispatch_requests (2.6.21-rc2 and 2.6.20) | Date | Thu, 1 Mar 2007 13:08:27 +0100 |
| |
Am Mittwoch, 28. Februar 2007 19:02 schrieb Dan Williams: > I can reliably reproduce a null pointer dereference on 2.6.20 and > 2.6.21-rc2. I will keep digging to find the kernel version where > this last worked, but wanted to see if there were any immediate > experiments I should try. > ... > Kernel 2.6.21-rc2 on an i686 > ... > [ 431.709022] BUG: unable to handle kernel NULL pointer dereference > at virtual address 0000005c [ 431.717993] printing eip: > ... > [ 431.825386] EIP is at cfq_dispatch_insert+0xb/0x53 > ... > [ 431.887396] [<c01e1fc9>] cfq_dispatch_requests+0x138/0x3f0 Hi, unfortunately i yet don't really have much/enough knowledge of cfq and the kernels inwards at the moment... but looking at cfq_dispatch_insert+0xb it seems the struct request pointer given (as second parameter by cfq_dispatch_request) was NULL and dereferencing it in the RQ_CFQQ macro leads to this oops.
The "break"-out patch below for __cfq_dispatch_request might be at least a possible workaround for this, but it could also be total bullsh.. Perhaps someone smarter might pick this up.. and give a real fix.
Have fun, Frank ---
block/cfq-iosched.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletion(-)
Index: linux-2.6/block/cfq-iosched.c =================================================================== --- linux-2.6.orig/block/cfq-iosched.c +++ linux-2.6/block/cfq-iosched.c @@ -962,7 +962,8 @@ __cfq_dispatch_requests(struct cfq_data * follow expired path, else get first next available */ if ((rq = cfq_check_fifo(cfqq)) == NULL) - rq = cfqq->next_rq; + if ((rq = cfqq->next_rq) == NULL) + break;
/* * finally, insert request into driver dispatch list - 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/
| |