linux-kernel - Re: [PATCH 1/2] drivers: base: power: main: Use built-in RCU list checking

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Date:   Sun, 1 Mar 2020 21:12:53 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     madhuparnabhowmik10@...il.com,
        Joel Fernandes <joel@...lfernandes.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        frextrite@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org, paulmck@...nel.org
Subject: Re: [PATCH 1/2] drivers: base: power: main: Use built-in RCU list checking

On Fri, Feb 28, 2020 at 6:47 PM <madhuparnabhowmik10@...il.com> wrote:
>
> From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
>
> This patch passes the cond argument to list_for_each_entry_rcu()
> to fix the following false-positive lockdep warnings:
>
> [  330.302784] =============================
> [  330.302789] WARNING: suspicious RCU usage
> [  330.302796] 5.6.0-rc1+ #5 Not tainted
> [  330.302801] -----------------------------
> [  330.302808] drivers/base/power/main.c:326 RCU-list traversed in non-reader section!!
>
> [  330.303303] =============================
> [  330.303307] WARNING: suspicious RCU usage
> [  330.303311] 5.6.0-rc1+ #5 Not tainted
> [  330.303315] -----------------------------
> [  330.303319] drivers/base/power/main.c:1698 RCU-list traversed in non-reader section!!
>
> [  331.934969] =============================
> [  331.934971] WARNING: suspicious RCU usage
> [  331.934973] 5.6.0-rc1+ #5 Not tainted
> [  331.934975] -----------------------------
> [  331.934977] drivers/base/power/main.c:1238 RCU-list traversed in non-reader section!!
>
> [  332.467772] WARNING: suspicious RCU usage
> [  332.467775] 5.6.0-rc1+ #5 Not tainted
> [  332.467775] -----------------------------
> [  332.467778] drivers/base/power/main.c:269 RCU-list traversed in non-reader section!!

I don't see these warnings in the kernels run locally here.

What do you do to get them?

Joel, any comments here?

>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> ---
>  drivers/base/power/main.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 0e99a760aebd..742c05f3c1e7 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -266,7 +266,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
>          * callbacks freeing the link objects for the links in the list we're
>          * walking.
>          */
> -       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
> +       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
> +                               device_links_read_lock_held())
>                 if (READ_ONCE(link->status) != DL_STATE_DORMANT)
>                         dpm_wait(link->supplier, async);
>
> @@ -323,7 +324,8 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
>          * continue instead of trying to continue in parallel with its
>          * unregistration).
>          */
> -       list_for_each_entry_rcu(link, &dev->links.consumers, s_node)
> +       list_for_each_entry_rcu(link, &dev->links.consumers, s_node,
> +                                device_links_read_lock_held())
>                 if (READ_ONCE(link->status) != DL_STATE_DORMANT)
>                         dpm_wait(link->consumer, async);
>
> @@ -1235,7 +1237,8 @@ static void dpm_superior_set_must_resume(struct device *dev)
>
>         idx = device_links_read_lock();
>
> -       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
> +       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
> +                                device_links_read_lock_held())
>                 link->supplier->power.must_resume = true;
>
>         device_links_read_unlock(idx);
> @@ -1695,7 +1698,8 @@ static void dpm_clear_superiors_direct_complete(struct device *dev)
>
>         idx = device_links_read_lock();
>
> -       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node) {
> +       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
> +                                device_links_read_lock_held()) {
>                 spin_lock_irq(&link->supplier->power.lock);
>                 link->supplier->power.direct_complete = false;
>                 spin_unlock_irq(&link->supplier->power.lock);
> --
> 2.17.1
>