linux-kernel - Re: [PATCH rcu 10/18] srcutiny: Mark read-side data races

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YQJlbEgaAGJvx3iN@boqun-archlinux>
Date:   Thu, 29 Jul 2021 16:23:08 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org
Subject: Re: [PATCH rcu 10/18] srcutiny: Mark read-side data races

On Wed, Jul 21, 2021 at 01:21:18PM -0700, Paul E. McKenney wrote:
> This commit marks some interrupt-induced read-side data races in
> __srcu_read_lock(), __srcu_read_unlock(), and srcu_torture_stats_print().
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  include/linux/srcutiny.h | 8 ++++----
>  kernel/rcu/srcutiny.c    | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
> index 0e0cf4d6a72a0..6cfaa0a9a9b96 100644
> --- a/include/linux/srcutiny.h
> +++ b/include/linux/srcutiny.h
> @@ -61,7 +61,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
>  	int idx;
>  
>  	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> -	WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
> +	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
>  	return idx;
>  }
>  
> @@ -81,11 +81,11 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
>  {
>  	int idx;
>  
> -	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> +	idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;

This looks very weird, any explanation why we want to put data_race() on
a READ_ONCE()?

Regards,
Boqun

>  	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
>  		 tt, tf, idx,
> -		 READ_ONCE(ssp->srcu_lock_nesting[!idx]),
> -		 READ_ONCE(ssp->srcu_lock_nesting[idx]));
> +		 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
> +		 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
>  }
>  
>  #endif
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 26344dc6483b0..a0ba2ed49bc61 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -96,7 +96,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
>   */
>  void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
>  {
> -	int newval = ssp->srcu_lock_nesting[idx] - 1;
> +	int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
>  
>  	WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
>  	if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
> -- 
> 2.31.1.189.g2e36527f23
>