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

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Message-ID: <20250826125541.7143e172c124.I9ecf55da46ccf33778f2c018a82e1819d815b348@changeid>
Date: Tue, 26 Aug 2025 12:55:31 +0200
From: Johannes Berg <johannes@...solutions.net>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: 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: [PATCH] PM: sleep: annotate RCU list iterations

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>
---
Honestly, not sure, maybe this should just be without _rcu?
---
 drivers/base/power/main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index dbf5456cd891..e80175486be7 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -675,7 +675,8 @@ 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(link, &dev->links.consumers, s_node,
+				device_links_read_lock_held())
 		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
 			dpm_async_with_cleanup(link->consumer, func);
 
@@ -1330,7 +1331,8 @@ 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(link, &dev->links.suppliers, c_node,
+				device_links_read_lock_held())
 		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
 			dpm_async_with_cleanup(link->supplier, func);
 
-- 
2.51.0