From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Alexander Gordeev <agordeev@redhat.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] rcu: Cleanup RCU tree initialization
Date: Mon, 9 Mar 2015 16:49:43 -0700 [thread overview]
Message-ID: <20150309234943.GA23932@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150309233947.GA16995@linux.vnet.ibm.com>
On Mon, Mar 09, 2015 at 04:39:47PM -0700, Paul E. McKenney wrote:
> On Mon, Mar 09, 2015 at 02:40:21PM -0700, Paul E. McKenney wrote:
> > On Mon, Mar 09, 2015 at 09:34:04AM +0100, Alexander Gordeev wrote:
> > > Hi Paul,
> > >
> > > Here is cleanup of RCU tree initialization rebased on linux-rcu rcu/next
> > > repo, as you requested. Please, note an extra patch #10 that was not
> > > present in the first post.
> > >
> > > The series successfully passes kernel build test with CONFIG_RCU_FANOUT
> > > and CONFIG_RCU_FANOUT_LEAF equal to 5.
> >
> > I queued up 1-9, as discussed and have started testing. I will let you
> > know how it goes.
>
> Initial testing went well except for the following warning:
>
> /home/paulmck/public_git/linux-rcu/kernel/rcu/tree.c: In function ‘rcu_init_one.isra.63’:
> /home/paulmck/public_git/linux-rcu/kernel/rcu/tree.c:3961:3: warning: ‘levelcnt[0]’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> for (j = 0; j < levelcnt[i]; j++, rnp++) {
>
> This warning looks like a false positive to me, given that the loop
> near the beginning of the function initializes levelcnt[0]. Am I
> missing something here, and either way, what is the best way to shut
> this warning up?
My suggestion is the following:
if (rcu_num_lvls <= 0)
panic("rcu_init_one: rcu_num_lvls underflow");
Just following the other panic() in rcu_init_one().
Thanx, Paul
> I am using gcc version 4.8.2.
>
> This warning only appears for some configurations.
> SRCU-N: Four CPUs, single rcu_node structure.
> SRCU-P: Eight CPUs, single rcu_node structure.
> TASKS01: Two CPUs, single rcu_node structure.
> TASKS03: Two CPUs, single rcu_node structure.
> TREE09: Single CPU, single rcu_node structure.
>
> All the other TREE0N configurations have multiple rcu_node structures.
>
> TASKS02 didn't warn either despite having only one CPU, but that is
> because it uses Tiny RCU instead of Tree RCU.
>
> So this warning shows up only in the case where the compiler knows
> that the rcu_node tree consists of only one rcu_node structure.
>
> Thanx, Paul
>
> > > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > >
> > >
> > > Alexander Gordeev (10):
> > > rcu: Panic if RCU tree can not accommodate all CPUs
> > > rcu: Remove superfluous local variable in rcu_init_geometry()
> > > rcu: Cleanup rcu_init_geometry() code and arithmetics
> > > rcu: Simplify rcu_init_geometry() capacity arithmetics
> > > rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items
> > > rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items
> > > rcu: Remove unnecessary fields from rcu_state structure
> > > rcu: Limit count of static data to the number of RCU levels
> > > rcu: Simplify arithmetic to calculate number of RCU nodes
> > > rcu: Remove unnecessary grpnum field from rcu_node structure
> > >
> > > kernel/rcu/tree.c | 102 ++++++++++++++++++++---------------------------
> > > kernel/rcu/tree.h | 35 ++++++++--------
> > > kernel/rcu/tree_plugin.h | 4 +-
> > > 3 files changed, 63 insertions(+), 78 deletions(-)
> > >
> > > --
> > > 1.8.3.1
> > >
next prev parent reply other threads:[~2015-03-09 23:49 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-09 8:34 [PATCH 00/10] rcu: Cleanup RCU tree initialization Alexander Gordeev
2015-03-09 8:34 ` [PATCH 01/10] rcu: Panic if RCU tree can not accommodate all CPUs Alexander Gordeev
2015-03-09 8:34 ` [PATCH 02/10] rcu: Remove superfluous local variable in rcu_init_geometry() Alexander Gordeev
2015-03-09 8:34 ` [PATCH 03/10] rcu: Cleanup rcu_init_geometry() code and arithmetics Alexander Gordeev
2015-03-09 8:34 ` [PATCH 04/10] rcu: Simplify rcu_init_geometry() capacity arithmetics Alexander Gordeev
2015-03-09 8:34 ` [PATCH 05/10] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items Alexander Gordeev
2015-03-09 8:34 ` [PATCH 06/10] rcu: Limit rcu_capacity[] size " Alexander Gordeev
2015-03-09 8:34 ` [PATCH 07/10] rcu: Remove unnecessary fields from rcu_state structure Alexander Gordeev
2015-03-09 8:34 ` [PATCH 08/10] rcu: Limit count of static data to the number of RCU levels Alexander Gordeev
2015-03-09 8:34 ` [PATCH 09/10] rcu: Simplify arithmetic to calculate number of RCU nodes Alexander Gordeev
2015-03-09 8:34 ` [PATCH 10/10] rcu: Remove unnecessary grpnum field from rcu_node structure Alexander Gordeev
2015-03-09 9:36 ` [PATCH 00/10] rcu: Cleanup RCU tree initialization Alexander Gordeev
2015-03-09 21:35 ` Paul E. McKenney
2015-03-10 14:33 ` Alexander Gordeev
2015-03-10 14:57 ` Paul E. McKenney
2015-03-09 21:40 ` Paul E. McKenney
2015-03-09 23:39 ` Paul E. McKenney
2015-03-09 23:49 ` Paul E. McKenney [this message]
2015-03-10 4:43 ` Paul E. McKenney
2015-03-10 14:39 ` Alexander Gordeev
2015-03-10 14:52 ` Paul E. McKenney
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