Re: automount hangs during boot somewhere in rcu_barrier.

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jun 05, 2012 at 08:19:30AM -0700, Paul E. McKenney wrote:
> On Tue, Jun 05, 2012 at 12:46:58PM +0300, Gleb Natapov wrote:
> > On Mon, Jun 04, 2012 at 07:54:32AM -0700, Paul E. McKenney wrote:
> > > On Mon, Jun 04, 2012 at 01:09:25PM +0300, Gleb Natapov wrote:
> > > > On Mon, Jun 04, 2012 at 10:48:03AM +0300, Gleb Natapov wrote:
> > > > > On Sun, Jun 03, 2012 at 08:15:49PM -0700, Paul E. McKenney wrote:
> > > > > > Hmmm...  Could you please try disabling CONFIG_RCU_FAST_NO_HZ?  If that
> > > > > > makes the problem go away, I have some patches 3.6-targeted patches
> > > > > > for you.
> > > > > Will report back.
> > > > > 
> > > > Do not see any problems with the option disabled.
> > > 
> > > OK, then you are probably being bitten by the same bug that was biting
> > > Pascal and Heiko.  Could you please apply the following series from -rcu?
> > > 
> > > 	bf7757c3 (Merge commit 'v3.4-rc6' into HEAD)
> > > 	edc17350 (RCU_FAST_NO_HZ detection of callback adoption)
> > > 	8e03a88e (Update RCU_FAST_NO_HZ tracing for lazy callbacks)
> > > 	f2298c63 (Move RCU_FAST_NO_HZ per-CPU variables to rcu_dynticks structure)
> > > 	05cc0fc9 (Precompute RCU_FAST_NO_HZ timer offsets)
> > > 	477fca01 (Dump only the current CPU's buffers for idle-entry/exit warnings)
> > > 	f29075fb (The rcu_needs_cpu() function is not a quiescent state)
> > > 
> > > Of these, 05cc0fc9 (Precompute RCU_FAST_NO_HZ timer offsets) is likely
> > > to be the most relevant.  The -rcu tree may be found at:
> > > 
> > > 	git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> > > 
> > > Please let me know if you have any trouble pulling this series.
> > > 
> > The problem is gone with the series + enabling CONFIG_RCU_FAST_NO_HZ
> > back.
> 
> Very good!!!
> 
> Maybe I should be submitting this series to 3.5 rather than 3.6?
> 
As it stands now I cannot use kernels with CONFIG_RCU_FAST_NO_HZ
enabled. May be disabling it is a good enough workaround for poor souls
like me, but I doubt distros can enable it with known problems like
that.

Thanks you for your promptly response!

--
			Gleb.