[PATCH RFC v2] firmware_loader: Fix recursive lock in device_cache_fw_images()

["syzbot" <syzbot@kernel.org>]

A recursive locking deadlock can occur in the firmware loader's power
management notification handler.

During system suspend or hibernation preparation, fw_pm_notify() calls
device_cache_fw_images(). This function acquires fw_lock to set the
firmware cache state to FW_LOADER_START_CACHE and then iterates over
all devices using dpm_for_each_dev() while still holding the lock.

For each device, dev_cache_fw_image() schedules asynchronous work to
cache the firmware. If memory allocation for the async work entry fails
(e.g., in out-of-memory conditions), async_schedule_node_domain()
falls back to executing the work function synchronously in the current
thread.

The synchronous execution path (__async_dev_cache_fw_image() ->
cache_firmware() -> request_firmware() -> assign_fw()) attempts
to acquire fw_lock again. Since the current thread already holds
fw_lock, this results in a recursive locking deadlock.

Fix this by releasing fw_lock immediately after updating the cache
state and before calling dpm_for_each_dev(). The lock is only needed
to protect the state update. Concurrent firmware requests will correctly
see the FW_LOADER_START_CACHE state and use the piggyback mechanism,
which is independently protected by its own fwc->name_lock.

Fixes: ac39b3ea73aacde876d1d5ee1ca3e2719f771482 ("firmware loader: let caching firmware piggyback on loading firmware")
Assisted-by: Gemini:gemini-3.1-pro-preview Gemini:gemini-3-flash-preview
Reported-by: syzbot+e70e4c6f6eee43357ba7@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=e70e4c6f6eee43357ba7
Link: https://syzkaller.appspot.com/ai_job?id=8cbf9f7d-812d-4db3-89fa-0aaef3ce3a2f
To: <gregkh@linuxfoundation.org>
To: <linux-kernel@vger.kernel.org>
To: <rafael@kernel.org>
Cc: <dakr@kernel.org>
Cc: <driver-core@lists.linux.dev>
Cc: <mcgrof@kernel.org>
Cc: <russ.weight@linux.dev>

---
v2:
- Removed the empty comment after dpm_for_each_dev().

v1:
https://lore.kernel.org/all/7b8b3fbf-950b-4418-8cf1-772a4d639b14@mail.kernel.org/T/
---
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index a11b30dda..c96312ac2 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -1503,9 +1503,10 @@ static void device_cache_fw_images(void)
 
 	mutex_lock(&fw_lock);
 	fwc->state = FW_LOADER_START_CACHE;
-	dpm_for_each_dev(NULL, dev_cache_fw_image);
 	mutex_unlock(&fw_lock);
 
+	dpm_for_each_dev(NULL, dev_cache_fw_image);
+
 	/* wait for completion of caching firmware for all devices */
 	async_synchronize_full_domain(&fw_cache_domain);
 


base-commit: 7fd2df204f342fc17d1a0bfcd474b24232fb0f32
-- 
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