Re: [3.12-rc] sg_open: leaving the kernel with locks still held!

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2013-10-23 at 05:11 -0700, Josh Boyer wrote:
> On Wed, Oct 23, 2013 at 12:44 AM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > On Tue, 2013-10-22 at 20:41 -0400, Douglas Gilbert wrote:
> >> On 13-10-22 04:56 PM, Simon Kirby wrote:
> >> > Hello!
> >> >
> >> > While trying to figure out why the request queue to sda (ext4) was
> >> > clogging up on one of our btrfs backup boxes, I noticed a megarc process
> >> > in D state, so enabled locking debugging, and got this (on 3.12-rc6):
> >> >
> >> > [  205.372823] ================================================
> >> > [  205.372901] [ BUG: lock held when returning to user space! ]
> >> > [  205.372979] 3.12.0-rc6-hw-debug-pagealloc+ #67 Not tainted
> >> > [  205.373055] ------------------------------------------------
> >> > [  205.373132] megarc.bin/5283 is leaving the kernel with locks still held!
> >> > [  205.373212] 1 lock held by megarc.bin/5283:
> >> > [  205.373285]  #0:  (&sdp->o_sem){.+.+..}, at: [<ffffffff8161e650>] sg_open+0x3a0/0x4d0
> >> >
> >> > Vaughan, it seems you touched this area last in 15b06f9a02406e, and git
> >> > tag --contains says this went in for 3.12-rc. We didn't see this on 3.11,
> >> > though I haven't tried with lockdep.
> >> >
> >> > This is caused by some of our internal RAID monitoring scripts that run
> >> > "megarc.bin -dispCfg -a0" (even though that controller isn't present on
> >> > this server -- a PowerEdge 2950 w/Perc 5).
> >> >
> >> > strace output of the program execution that causes the above message is
> >> > here: http://0x.ca/sim/ref/3.12-rc6/megarc_strace.txt
> >>
> >> This has been reported. That patch will be reverted or,
> >> if there is enough time, a fix will (or at least should)
> >> go in before the release of lk 3.12 .
> >
> > I think you've got about a week to prove you can fix it (before 3.12
> > goes final).  I'll send my current set of fixes to Linus without doing
> > anything about sg.
> 
> In the event that a suitable fix isn't found, are you going to revert
> the commit(s) that caused the issue?

That's what I said I'd do previously, yes.

James