linux-kernel - Re: [Xen-devel] swap: don't do discard if no discard option added

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Message-ID: <20120529144743.GG3558@phenom.dumpdata.com>
Date:	Tue, 29 May 2012 10:47:43 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	William Dauchy <wdauchy@...il.com>, shli@...ionio.com,
	stable@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	xen-devel@...ts.xensource.com, Shaohua Li <shli@...nel.org>,
	linux-kernel@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>
Subject: Re: [Xen-devel] swap: don't do discard if no discard option added

On Sat, May 26, 2012 at 11:29:37AM -0700, Hugh Dickins wrote:
> On Mon, 21 May 2012, Konrad Rzeszutek Wilk wrote:
> > On Mon, May 21, 2012 at 12:30:45AM +0200, William Dauchy wrote:
> > > Hello,
> > > 
> > > On Xen, when booting a guest with a system disk and an additional swap
> > > disk I'm getting a calltrace.
> > > xen hypervisor: 4.1.2; linux dom0: v3.3.6; linux guest: v3.2.17
> > > When booting without a swap disk, I don't have the issue.
> > > I also tested a guest with v3.3.6: same problem. But from v3.4-rc2,
> > > the issue is fixed.
> > > I cherry-picked:
> > 
> > > 052b198 swap: don't do discard if no discard option added
> > 
> > So you are asking for 052b198 to be back-ported.
> > 
> > I am OK with that but I think Shaohua needs to Ack that and
> > ask Greg to put it on stable@...nel.org
> 
> Since that commit did indeed go into v3.4, I won't quarrel with it
> now going to stable.
> 
> But the commit went in to work around the slow discard implementation
> on OCZ Vertex II SSDs.
> 
> Please, could someone explain to me the meaning of the stacktrace
> below (which is missing a WARNING or BUG line?), and how disabling
> swap discard fixes it?

I think I know and just narrowed down the issue this Friday.

William, could you please apply the patch outlined in
https://bugzilla.redhat.com/show_bug.cgi?id=824641
to your dom0 and see if that (so do not have 052b198 in your branch)

> 
> At present I see no connection (beyond the fact that the patch fixes
> the symptom): in the absence of understanding, I have to beware that
> the underlying issue may remain unfixed.

<nods>
> 
> Hugh
> 
> > 
> > 
> > 
> > > Applied and tested on top of v3.2.17 and v3.3.6, it fixes the issue.
> > > 
> > > Pid: 0, comm: swapper/0 Not tainted 3.2.17-x86_64 #12
> > > Call Trace:
> > >  <IRQ>
> > >  [<ffffffff810919da>] ? handle_irq_event_percpu+0x3a/0x140
> > >  [<ffffffff81091b29>] ? handle_irq_event+0x49/0x80
> > >  [<ffffffff81094e7d>] ? handle_edge_irq+0x6d/0x120
> > >  [<ffffffff81229088>] ? __xen_evtchn_do_upcall+0x1b8/0x280
> > >  [<ffffffff8122a442>] ? xen_evtchn_do_upcall+0x22/0x40
> > >  [<ffffffff8133f4fe>] ? xen_do_hypervisor_callback+0x1e/0x30
> > >  <EOI>
> > >  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
> > >  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
> > >  [<ffffffff8100768c>] ? xen_safe_halt+0xc/0x20
> > >  [<ffffffff81013563>] ? default_idle+0x23/0x40
> > >  [<ffffffff8100b073>] ? cpu_idle+0x63/0xb0
> > >  [<ffffffff81654c43>] ? start_kernel+0x362/0x36d
> > >  [<ffffffff81657491>] ? xen_start_kernel+0x558/0x55e
> > > Code: 39 ed 0f 84 1c 02 00 00 44 8b 7b 48 4c 8b 73 50 41 83 ef 01 41
> > > 21 ef 49 6b c7 70 4d 8b 64 06 40 49 69 c4 d0 00 00 00 48 8d 14 03 <48>
> > > 8b 8a 78 02 00 00 48 89 4c 24 10 80 ba 09 02 00 00 00 74 6d
> > > RIP  [<ffffffff8125ed66>] blkif_interrupt+0x66/0x320
> > >  RSP <ffff88001fc03e18>
> > > ---[ end trace dfd4e5623eb06620 ]---
> --
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