[bionic][PATCH 2/2] srcu: Lock srcu_data structure in srcu_gp_start()

[Marcelo Henrique Cerri]

My mistake. I used the patches that went into linux-azure to prepare it.

I will update it and re-submit it first thing in the morning.

On Wed, Feb 27, 2019 at 10:38:23AM +0100, Stefan Bader wrote:
> On 21.02.19 00:28, Marcelo Henrique Cerri wrote:
> > From: Dennis Krein <Dennis.Krein at netapp.com>
> > 
> > BugLink: http://bugs.launchpad.net/bugs/1802021
> > 
> > The srcu_gp_start() function is called with the srcu_struct structure's
> > ->lock held, but not with the srcu_data structure's ->lock.  This is
> > problematic because this function accesses and updates the srcu_data
> > structure's ->srcu_cblist, which is protected by that lock.  Failing to
> > hold this lock can result in corruption of the SRCU callback lists,
> > which in turn can result in arbitrarily bad results.
> > 
> > This commit therefore makes srcu_gp_start() acquire the srcu_data
> > structure's ->lock across the calls to rcu_segcblist_advance() and
> > rcu_segcblist_accelerate(), thus preventing this corruption.
> > 
> > Reported-by: Bart Van Assche <bvanassche at acm.org>
> > Reported-by: Christoph Hellwig <hch at infradead.org>
> > Reported-by: Sebastian Kuzminsky <seb.kuzminsky at gmail.com>
> > Signed-off-by: Dennis Krein <Dennis.Krein at netapp.com>
> > Signed-off-by: Paul E. McKenney <paulmck at linux.ibm.com>
> > Tested-by: Dennis Krein <Dennis.Krein at netapp.com>
> > Cc: <stable at vger.kernel.org> # 4.16.x
> > (cherry picked from commit eb4c2382272ae7ae5d81fdfa5b7a6c86146eaaa4)
> > Acked-by: Stefan Bader <stefan.bader at canonical.com>
> > Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> > Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
> > ---
> 
> Cannot remember having acked this yet...
> 
> >  kernel/rcu/srcutree.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index d5cea81378cc..b3e5e9873582 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -441,10 +441,12 @@ static void srcu_gp_start(struct srcu_struct *sp)
> >  
> >  	lockdep_assert_held(&sp->lock);
> >  	WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed));
> > +	spin_lock_rcu_node(sdp);  /* Interrupts already disabled. */
> >  	rcu_segcblist_advance(&sdp->srcu_cblist,
> >  			      rcu_seq_current(&sp->srcu_gp_seq));
> >  	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
> >  				       rcu_seq_snap(&sp->srcu_gp_seq));
> > +	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */
> >  	smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
> >  	rcu_seq_start(&sp->srcu_gp_seq);
> >  	state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));
> > 
> 
> 




-- 
Regards,
Marcelo

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