[PATCH] rcu/nocb: Fix uninitialized variable in nocb_gp_wait()

[PATCH] rcu/nocb: Fix uninitialized variable in nocb_gp_wait()

[Dan Carpenter]

We never set this to false.  This probably doesn't affect most people's
runtime because GCC will automatically initialize it to false at certain
common optimization levels.  But that behavior is related to a bug in
GCC and obviously should not be relied on.

Fixes: 5d6742b37727 ("rcu/nocb: Use rcu_segcblist for no-CBs CPUs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 2defc7fe74c3..fa08d55f7040 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1946,7 +1946,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	int __maybe_unused cpu = my_rdp->cpu;
 	unsigned long cur_gp_seq;
 	unsigned long flags;
-	bool gotcbs;
+	bool gotcbs = false;
 	unsigned long j = jiffies;
 	bool needwait_gp = false; // This prevents actual uninitialized use.
 	bool needwake;
-- 
2.20.1

Re: [PATCH] rcu/nocb: Fix uninitialized variable in nocb_gp_wait()

[Paul E. McKenney]

On Mon, Sep 23, 2019 at 05:26:34PM +0300, Dan Carpenter wrote:
> We never set this to false.  This probably doesn't affect most people's
> runtime because GCC will automatically initialize it to false at certain
> common optimization levels.  But that behavior is related to a bug in
> GCC and obviously should not be relied on.
> 
> Fixes: 5d6742b37727 ("rcu/nocb: Use rcu_segcblist for no-CBs CPUs")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Good catch!  Queued for v5.5, thank you!

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 2defc7fe74c3..fa08d55f7040 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1946,7 +1946,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
>  	int __maybe_unused cpu = my_rdp->cpu;
>  	unsigned long cur_gp_seq;
>  	unsigned long flags;
> -	bool gotcbs;
> +	bool gotcbs = false;
>  	unsigned long j = jiffies;
>  	bool needwait_gp = false; // This prevents actual uninitialized use.
>  	bool needwake;
> -- 
> 2.20.1
>