linux-kernel - Re: [lkp] [printk] 34578dc67f: EIP is at vprintk

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Message-ID: <20160224151242.GA2254@swordfish>
Date:	Thu, 25 Feb 2016 00:12:42 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	kernel test robot <ying.huang@...ux.intel.com>, lkp@...org,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Calvin Owens <calvinowens@...com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Kyle McMartin <kyle@...nel.org>, Tejun Heo <tj@...nel.org>,
	Jan Kara <jack@...e.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [lkp] [printk] 34578dc67f: EIP is at vprintk_emit+0x1ea/0x600

On (02/24/16 21:50), Sergey Senozhatsky wrote:
> On (02/24/16 12:46), Petr Mladek wrote:
> [..]
> > > and you get the NMI watchdog softlockup because you have a whole bunch of
> > > 
> > >    "of_overlay_destroy: Could not find overlay #6"
> > >    "### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6"
> > > 
> > > messages to print. seems that somehitng just pushes them in a loop.
> > > there are too many of them:
> > 
> > This sounds like a reasonable explanation. It seems that
> > of_unittest_destroy_tracked_overlays() really ended in an infinite
> > loop.
> > 
> > But I am still curious why the softlookup points to
> > 
> > [   33.497718] EIP is at vprintk_emit+0x1ea/0x600
> > 
> > Also there is on the stack
> > 
> > [   33.497741]  [<c068e712>] vprintk_default+0x32/0x40
> > [   33.497741]  [<c068e712>] vprintk_default+0x32/0x40
> > [   33.497744]  [<c06fdf6e>] printk+0x11/0x13
> > [   33.497744]  [<c06fdf6e>] printk+0x11/0x13
> > [   33.497748]  [<c0df5eec>] of_unittest_overlay+0x8d1/0x900
> > [   33.497748]  [<c0df5eec>] of_unittest_overlay+0x8d1/0x900
> > [   33.497750]  [<c0df6b1f>] of_unittest+0xc04/0xc2d
> > [   33.497750]  [<c0df6b1f>] of_unittest+0xc04/0xc2d
> > 
> > I would expect that the soft lookup happens in console_unlock()
> > called with IRQs disabled. It seems to me that of_unittest_overlay()
> > is called with IRQs enabled.

hm... both of the logbuf_lock/irq reqions in vprintk_emit/console_unlock
are not modified by the patch set. there is, however, one thing that has
changed -- additional console_cont_flush() calls, which does spin_lock_irq
logbuf_lock and spin_unlock_irq logbuf_lock.

> > I want to be sure that the patch in printk() did not introduce
> > a deadlock that is visible only under a high printk load.

I'll do more tests, certainly.

	-ss