linux-kernel - Re: [PATCH v2] PM: sleep: annotate RCU list iterations

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Message-ID: <CAJZ5v0iOibiTMpzPGb27YtPRkKF0jdbE7TNOW_ceUk1Ov5abWg@mail.gmail.com>
Date: Tue, 26 Aug 2025 15:36:53 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Johannes Berg <johannes@...solutions.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>, Len Brown <lenb@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH v2] PM: sleep: annotate RCU list iterations

On Tue, Aug 26, 2025 at 1:43 PM Johannes Berg <johannes@...solutions.net> wrote:
>
> From: Johannes Berg <johannes.berg@...el.com>
>
> These iterations require the read lock, otherwise RCU
> lockdep will splat:
>
> =============================
> WARNING: suspicious RCU usage
> 6.17.0-rc3-00014-g31419c045d64 #6 Tainted: G           O
> -----------------------------
> drivers/base/power/main.c:1333 RCU-list traversed in non-reader section!!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> 5 locks held by rtcwake/547:
>  #0: 00000000643ab418 (sb_writers#6){.+.+}-{0:0}, at: file_start_write+0x2b/0x3a
>  #1: 0000000067a0ca88 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x181/0x24b
>  #2: 00000000631eac40 (kn->active#3){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x191/0x24b
>  #3: 00000000609a1308 (system_transition_mutex){+.+.}-{4:4}, at: pm_suspend+0xaf/0x30b
>  #4: 0000000060c0fdb0 (device_links_srcu){.+.+}-{0:0}, at: device_links_read_lock+0x75/0x98
>
> stack backtrace:
> CPU: 0 UID: 0 PID: 547 Comm: rtcwake Tainted: G           O        6.17.0-rc3-00014-g31419c045d64 #6 VOLUNTARY
> Tainted: [O]=OOT_MODULE
> Stack:
>  223721b3a80 6089eac6 00000001 00000001
>  ffffff00 6089eac6 00000535 6086e528
>  721b3ac0 6003c294 00000000 60031fc0
> Call Trace:
>  [<600407ed>] show_stack+0x10e/0x127
>  [<6003c294>] dump_stack_lvl+0x77/0xc6
>  [<6003c2fd>] dump_stack+0x1a/0x20
>  [<600bc2f8>] lockdep_rcu_suspicious+0x116/0x13e
>  [<603d8ea1>] dpm_async_suspend_superior+0x117/0x17e
>  [<603d980f>] device_suspend+0x528/0x541
>  [<603da24b>] dpm_suspend+0x1a2/0x267
>  [<603da837>] dpm_suspend_start+0x5d/0x72
>  [<600ca0c9>] suspend_devices_and_enter+0xab/0x736
>  [...]
>
> Add the fourth argument to the iteration to annotate
> this and avoid the splat.
>
> Fixes: 06799631d522 ("PM: sleep: Make async suspend handle suppliers like parents")
> Fixes: ed18738fff02 ("PM: sleep: Make async resume handle consumers like children")
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> ---
> v2: use list_for_each_entry_rcu_locked()
> ---
>  drivers/base/power/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index dbf5456cd891..2ea6e05e6ec9 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -675,7 +675,7 @@ static void dpm_async_resume_subordinate(struct device *dev, async_func_t func)
>         idx = device_links_read_lock();
>
>         /* Start processing the device's "async" consumers. */
> -       list_for_each_entry_rcu(link, &dev->links.consumers, s_node)
> +       list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
>                 if (READ_ONCE(link->status) != DL_STATE_DORMANT)
>                         dpm_async_with_cleanup(link->consumer, func);
>
> @@ -1330,7 +1330,7 @@ static void dpm_async_suspend_superior(struct device *dev, async_func_t func)
>         idx = device_links_read_lock();
>
>         /* Start processing the device's "async" suppliers. */
> -       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
> +       list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
>                 if (READ_ONCE(link->status) != DL_STATE_DORMANT)
>                         dpm_async_with_cleanup(link->supplier, func);
>
> --

Applied as 6.17-rc material, thanks!