Re: [Xen-devel] [PATCH] xen-blkback: free requests on disconnection

[Konrad Rzeszutek Wilk]

On Tue, Sep 08, 2015 at 12:43:41PM +0200, Roger Pau Monné wrote:
> El 07/09/15 a les 13.35, Bob Liu ha escrit:
> > 
> > On 09/07/2015 07:10 PM, Julien Grall wrote:
> >> On 07/09/15 07:07, Bob Liu wrote:
> >>> Hi Julien,
> >>
> >> Hi Bob,
> >>
> >>> On 09/04/2015 09:51 PM, Julien Grall wrote:
> >>>> Hi Roger,
> >>>>
> >>>> On 04/09/15 11:08, Roger Pau Monne wrote:
> >>>>> Request allocation has been moved to connect_ring, which is called every
> >>>>> time blkback connects to the frontend (this can happen multiple times during
> >>>>> a blkback instance life cycle). On the other hand, request freeing has not
> >>>>> been moved, so it's only called when destroying the backend instance. Due to
> >>>>> this mismatch, blkback can allocate the request pool multiple times, without
> >>>>> freeing it.
> >>>>>
> >>>>> In order to fix it, move the freeing of requests to xen_blkif_disconnect to
> >>>>> restore the symmetry between request allocation and freeing.
> >>>>>
> >>>>> Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
> >>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >>>>> Cc: Julien Grall <julien.grall@xxxxxxxxxx>
> >>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >>>>> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> >>>>> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> >>>>
> >>>> The patch is fixing my problem when using UEFI in the guest. Thank you!
> >>>>
> >>>
> >>> Could you please explain the problem you met a bit more?
> >>> So that I can know back port this patch if met similar issue.
> >>
> >> This is related to commit 86839c56dee28c315a4c19b7bfee450ccd84cd25
> >> "xen/block: add multi-page ring support" (Roger, it may be worth to
> >> indicate the offending commit in you commit message).
> >>
> >> When starting a guest using UEFI. After the domain is destroyed I get
> >> the following warning from blkback:
> >>
> >>
> >> ------------[ cut here ]------------
> >> WARNING: CPU: 2 PID: 95 at
> >> /home/julien/works/linux/drivers/block/xen-blkback/xenbus.c:274
> >> xen_blkif_deferred_free+0x1f4/0x1f8()
> >> Modules linked in:
> >> CPU: 2 PID: 95 Comm: kworker/2:1 Tainted: G        W       4.2.0 #85
> >> Hardware name: APM X-Gene Mustang board (DT)
> >> Workqueue: events xen_blkif_deferred_free
> >> Call trace:
> >> [<ffff8000000890a8>] dump_backtrace+0x0/0x124
> >> [<ffff8000000891dc>] show_stack+0x10/0x1c
> >> [<ffff8000007653bc>] dump_stack+0x78/0x98
> >> [<ffff800000097e88>] warn_slowpath_common+0x9c/0xd4
> >> [<ffff800000097f80>] warn_slowpath_null+0x14/0x20
> >> [<ffff800000557a0c>] xen_blkif_deferred_free+0x1f0/0x1f8
> >> [<ffff8000000ad020>] process_one_work+0x160/0x3b4
> >> [<ffff8000000ad3b4>] worker_thread+0x140/0x494
> >> [<ffff8000000b2e34>] kthread+0xd8/0xf0
> >> ---[ end trace 6f859b7883c88cdd ]---
> >>
> >> This is because the allocation of the requests are done during the
> >> connection but the free is done when the domain is destroyed. Therefore
> >> if the domain is re-initializing the connection (because UEFI or PV Grub
> >> is used), the request won't be free and kept until the end.
> >>
> > 
> > Thank you!
> > Roger, I think it's better to have this information in your commit message too.
> 
> Konrad, would you like me to resend the patch with the modified commit
> message, or do you plan to amend it yourself while committing?

I will amend it. Thanks!
> 
> Roger.
> 
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