On 18/3/5 04:23, Tejun Heo wrote:
> Hello, Joseph.
>
> Sorry about late reply.
>
> On Wed, Feb 28, 2018 at 02:52:10PM +0800, Joseph Qi wrote:
>> In current code, I'm afraid pd_offline_fn() as well as the rest
>> destruction have to be called together under the same blkcg->lock and
>>
Hello, Joseph.
Sorry about late reply.
On Wed, Feb 28, 2018 at 02:52:10PM +0800, Joseph Qi wrote:
> In current code, I'm afraid pd_offline_fn() as well as the rest
> destruction have to be called together under the same blkcg->lock and
> q->queue_lock.
> For example, if we split the
Hi Tejun,
On 18/2/28 02:33, Tejun Heo wrote:
> Hello, Joseph.
>
> On Sat, Feb 24, 2018 at 09:45:49AM +0800, Joseph Qi wrote:
>>> IIRC, as long as the blkcg and the device are there, the blkgs aren't
>>> gonna be destroyed. So, if you have a ref to the blkcg through
>>> tryget, the blkg
Hello, Joseph.
On Sat, Feb 24, 2018 at 09:45:49AM +0800, Joseph Qi wrote:
> > IIRC, as long as the blkcg and the device are there, the blkgs aren't
> > gonna be destroyed. So, if you have a ref to the blkcg through
> > tryget, the blkg shouldn't go away.
> >
>
> Maybe we have misunderstanding
Hi Tejun,
Could you please help take a look at this and give a confirmation?
Thanks,
Joseph
On 18/2/24 09:45, Joseph Qi wrote:
> Hi Tejun,
>
> On 18/2/23 22:23, Tejun Heo wrote:
>> Hello,
>>
>> On Fri, Feb 23, 2018 at 09:56:54AM +0800, xuejiufei wrote:
On Thu, Feb 22, 2018 at 02:14:34PM
Hi Tejun,
On 18/2/23 22:23, Tejun Heo wrote:
> Hello,
>
> On Fri, Feb 23, 2018 at 09:56:54AM +0800, xuejiufei wrote:
>>> On Thu, Feb 22, 2018 at 02:14:34PM +0800, Joseph Qi wrote:
I still don't get how css_tryget can work here.
The race happens when:
1) writeback kworker has
Hello,
On Fri, Feb 23, 2018 at 09:56:54AM +0800, xuejiufei wrote:
> > On Thu, Feb 22, 2018 at 02:14:34PM +0800, Joseph Qi wrote:
> >> I still don't get how css_tryget can work here.
> >>
> >> The race happens when:
> >> 1) writeback kworker has found the blkg with rcu;
> >> 2) blkcg is during
Hi Tejun,
On 2018/2/22 下午11:18, Tejun Heo wrote:
> Hello,
>
> On Thu, Feb 22, 2018 at 02:14:34PM +0800, Joseph Qi wrote:
>> I still don't get how css_tryget can work here.
>>
>> The race happens when:
>> 1) writeback kworker has found the blkg with rcu;
>> 2) blkcg is during offlining and
Hi Tejun,
Sorry for the delayed reply.
On 18/2/13 01:11, Tejun Heo wrote:
> Hello, Joseph.
>
> On Fri, Feb 09, 2018 at 10:15:19AM +0800, Joseph Qi wrote:
>> IIUC, we have to identify it is in blkcg_css_offline now which will
>> blkg_put. Since percpu_ref_kill_and_confirm in kill_css will set
Hello, Joseph.
On Fri, Feb 09, 2018 at 10:15:19AM +0800, Joseph Qi wrote:
> IIUC, we have to identify it is in blkcg_css_offline now which will
> blkg_put. Since percpu_ref_kill_and_confirm in kill_css will set flag
> __PERCPU_REF_DEAD, so we can use this to avoid the race. IOW, if
>
Hi Tejun,
On 18/2/8 23:23, Tejun Heo wrote:
> Hello, Joseph.
>
> On Thu, Feb 08, 2018 at 10:29:43AM +0800, Joseph Qi wrote:
>> So you mean checking css->refcnt to prevent the further use of
>> blkg_get? I think it makes sense.
>
> Yes.
>
>> IMO, we should use css_tryget_online instead, and
Hello, Joseph.
On Thu, Feb 08, 2018 at 10:29:43AM +0800, Joseph Qi wrote:
> So you mean checking css->refcnt to prevent the further use of
> blkg_get? I think it makes sense.
Yes.
> IMO, we should use css_tryget_online instead, and rightly after taking
Not really. An offline css still can
Hi Tejun,
Thanks very much for reviewing this patch.
On 18/2/8 05:38, Tejun Heo wrote:
> Hello, Joseph.
>
> On Wed, Feb 07, 2018 at 04:40:02PM +0800, Joseph Qi wrote:
>> writeback kworker
>> blkcg_bio_issue_check
>> rcu_read_lock
>> blkg_lookup
>> <<< *race window*
>>
Hello, Joseph.
On Wed, Feb 07, 2018 at 04:40:02PM +0800, Joseph Qi wrote:
> writeback kworker
> blkcg_bio_issue_check
> rcu_read_lock
> blkg_lookup
> <<< *race window*
> blk_throtl_bio
> spin_lock_irq(q->queue_lock)
> spin_unlock_irq(q->queue_lock)
>
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