[stgt] stgt: how to avoid WARNING at block/blk-core.c:1080

[Joe Eykholt]

On 8/3/10 12:40 PM, Joe Eykholt wrote:
> On 7/31/10 6:49 PM, FUJITA Tomonori wrote:
>> On Fri, 30 Jul 2010 10:32:34 -0700
>> Joe Eykholt<jeykholt at cisco.com> wrote:
>>
>>> Hi All,
>>>
>>> I'm working on a target module for scsi_tgt to work with libfc / fcoe
>>> in Linux 2.6.33.5. I'm missing some step in handling completion of
>>> a request.
>>>
>>> After each Inquiry or READ operation, in the transfer_response
>>> callback I send the data and response and then call the (*done)()
>>> routine.
>>>
>>> I figure I must be missing something, because I get this WARNING:
>>>
>>> [ 271.521650] ------------[ cut here ]------------
>>> [ 271.521658] WARNING: at block/blk-core.c:1080
>>> __blk_put_request+0x4f/0xbe()
>>> [ 271.521660] Hardware name:<snip>
>>> [ 271.521662] Modules linked in: libfc_tgt scsi_tgt nfs lockd nfs_acl
>>> auth_rpcgss autofs4 sunrpc ip6t_REJECT
>>> nf_conntrack_ipv6 ip6table_filter ip6_tables ipv6 dm_multipath uinput
>>> fnic libfcoe libfc enic i2c_i801
>>> iTCO_wdt serio_raw scsi_transport_fc iTCO_vendor_support pcspkr
>>> e1000e shpchp radeon ttm drm_kms_helper drm
>>> i2c_algo_bit i2c_core
>>> [ 271.521705] Pid: 2769, comm: scsi_tgtd/2 Tainted: G W 2.6.33.5-ftgt #9
>>> [ 271.521708] Call Trace:
>>> [ 271.521715] [<ffffffff811696ae>] ? __blk_put_request+0x4f/0xbe
>>> [ 271.521720] [<ffffffff81041462>] warn_slowpath_common+0x77/0xa4
>>> [ 271.521724] [<ffffffff8104149e>] warn_slowpath_null+0xf/0x11
>>> [ 271.521728] [<ffffffff811696ae>] __blk_put_request+0x4f/0xbe
>>> [ 271.521735] [<ffffffffa02b14b7>] scsi_host_put_command+0x52/0x80
>>> [scsi_tgt]
>>> [ 271.521740] [<ffffffffa02b14e5>] ? scsi_tgt_cmd_destroy+0x0/0x3f
>>> [scsi_tgt]
>>> [ 271.521745] [<ffffffffa02b151f>] scsi_tgt_cmd_destroy+0x3a/0x3f
>>> [scsi_tgt]
>>> [ 271.521751] [<ffffffff810513a0>] worker_thread+0x131/0x1bd
>>> [ 271.521756] [<ffffffff81054bfc>] ? autoremove_wake_function+0x0/0x38
>>> [ 271.521760] [<ffffffff8105126f>] ? worker_thread+0x0/0x1bd
>>> [ 271.521764] [<ffffffff810547fe>] kthread+0x7d/0x85
>>> [ 271.521770] [<ffffffff810099a4>] kernel_thread_helper+0x4/0x10
>>> [ 271.521774] [<ffffffff81054781>] ? kthread+0x0/0x85
>>> [ 271.521779] [<ffffffff810099a0>] ? kernel_thread_helper+0x0/0x10
>>> [ 271.521782] ---[ end trace 096013af4d0a82a0 ]---
>>>
>>> It's this code in block/blk-core.c:
>>>
>>> void __blk_put_request(struct request_queue *q, struct request *req)
>>> {
>>> if (unlikely(!q))
>>> return;
>>> if (unlikely(--req->ref_count))
>>> return;
>>>
>>> elv_completed_request(q, req);
>>>
>>> /* this is a bio leak */
>>> WARN_ON(req->bio != NULL);
>>>
>>> ...
>>>
>>> So, what should I be doing to tell the block layer that the request
>>> is done?
>>> Or, is there something that scsi_tgt should be doing to disassociate
>>> the bio
>>> from the req?
>>
>> Maybe we should call blk_end_request_all().
>>
>> But I don't think that bio is leaked in our case. So setting req->bio
>> to NULL might be fine.
>>
>> I can't access to my IBM POWER box now but I'll try later.
>
> I tried it with my module (not with ibmvstgt) and it seems to work better.
> Here's the patch I used (cut-and-paste from stg so for illustration only).
> Feel free to do something different. If setting rq->bio = NULL is OK,
> it might be better. I haven't researched this enough to know what's best.
>
> Author: Joe Eykholt <jeykholt at cisco.com>
> Date: Tue Aug 3 12:33:07 2010 -0700
>
> stgt: fix warning from __blk_put_request()
>
> Every ftgt I/O ending was getting a WARNING and stack dump
> from block/blk-core:1080 __blk_put_request() because a request
> still had a bio associated with it.
>
> Call blk_end_request_all() after unmapping the user pages.
>
> Signed-off-by: Joe Eykholt <jeykholt at cisco.com>
>
> diff --git a/drivers/scsi/scsi_tgt_lib.c b/drivers/scsi/scsi_tgt_lib.c
> index 1030327..a454ed0 100644
> --- a/drivers/scsi/scsi_tgt_lib.c
> +++ b/drivers/scsi/scsi_tgt_lib.c
> @@ -151,6 +151,7 @@ void scsi_host_put_command(struct Scsi_Host *shost,
> struct scsi_cmnd *cmd)
> kmem_cache_free(scsi_tgt_cmd_cache, tcmd);
>
> spin_lock_irqsave(q->queue_lock, flags);
> + __blk_end_request_all(rq, 0);
> __blk_put_request(q, rq);
> spin_unlock_irqrestore(q->queue_lock, flags);
>

Although that seemed to work on 2.6.35, when I tried it on
the fcoe-next tree, which is 2.6.35-rc3, it caused a crash due to
blk_update_request referencing a freed bio.  So, maybe just setting
rq->bio to NULL is correct.  If we freed the bio, we should do that
at the same place.   Just wanted to let you know that there's a
problem with the patch at this point.

       Joe

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