Re: kernel BUG at drivers/scsi/scsi_lib.c:1096!

Ming Lei
2015-11-23T00:36:21Z

On Mon, Nov 23, 2015 at 7:20 AM, Mark Salter <msalter@redhat.com> wrote:
> On Sun, 2015-11-22 at 00:56 +0800, Ming Lei wrote:
>> On Sat, 21 Nov 2015 12:30:14 +0100
>> Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:
>>
>> > On 20/11/2015 13:10, Michael Ellerman wrote:
>> > > On Thu, 2015-11-19 at 00:23 -0800, Christoph Hellwig wrote:
>> > >
>> > > > It's pretty much guaranteed a block layer bug, most likely in the
>> > > > merge bios to request infrastucture where we don't obey the merging
>> > > > limits properly.
>> > > >
>> > > > Does either of you have a known good and first known bad kernel?
>> > >
>> > > Not me, I've only hit it one or two times. All I can say is I have hit it in
>> > > 4.4-rc1.
>> > >
>> > > Laurent, can you narrow it down at all?
>> >
>> > It seems that the panic is triggered by the commit bdced438acd8 ("block:
>> > setup bi_phys_segments after splitting") which has been pulled by the
>> > merge d9734e0d1ccf ("Merge branch 'for-4.4/core' of
>> > git://git.kernel.dk/linux-block").
>> >
>> > My system is panicing promptly when running a kernel built at
>> > d9734e0d1ccf, while reverting the commit bdced438acd8, it can run hours
>> > without panicing.
>> >
>> > This being said, I can't explain what's going wrong.
>> >
>> > May Ming shed some light here ?
>>
>> Laurent, looks there is one bug in blk_bio_segment_split(), would you
>> mind testing the following patch to see if it fixes your issue?
>>
>> ---
>> From 6fc701231dcc000bc8bc4b9105583380d9aa31f4 Mon Sep 17 00:00:00 2001
>> From: Ming Lei <ming.lei@canonical.com>
>> Date: Sun, 22 Nov 2015 00:47:13 +0800
>> Subject: [PATCH] block: fix segment split
>>
>> Inside blk_bio_segment_split(), previous bvec pointer('bvprvp')
>> always points to the iterator local variable, which is obviously
>> wrong, so fix it by pointing to the local variable of 'bvprv'.
>>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>> block/blk-merge.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-merge.c b/block/blk-merge.c
>> index de5716d8..f2efe8a 100644
>> --- a/block/blk-merge.c
>> +++ b/block/blk-merge.c
>> @@ -98,7 +98,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
>>
>> seg_size += bv.bv_len;
>> bvprv = bv;
>> - bvprvp = &bv;
>> + bvprvp = &bvprv;
>> sectors += bv.bv_len >> 9;
>> continue;
>> }
>> @@ -108,7 +108,7 @@ new_segment:
>>
>> nsegs++;
>> bvprv = bv;
>> - bvprvp = &bv;
>> + bvprvp = &bvprv;
>> seg_size = bv.bv_len;
>> sectors += bv.bv_len >> 9;
>> }
>
> I'm still hitting the BUG even with this patch applied on top of 4.4-rc1.

OK, looks there are still other bugs, care to share us how to reproduce
it on arm64?

thanks,
Ming