Message-ID: <20251025160905.3857885-336-sashal@kernel.org>
Date: Sat, 25 Oct 2025 11:59:27 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Sasha Levin <sashal@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.17-5.4] extcon: adc-jack: Fix wakeup source leaks on device unbind

From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

[ Upstream commit 78b6a991eb6c6f19ed7d0ac91cda3b3b117fda8f ]

Device can be unbound, so driver must also release memory for the wakeup
source.  Do not use devm interface, because it would change the order of
cleanup.

Link: https://lore.kernel.org/lkml/20250501-device-wakeup-leak-extcon-v2-1-7af77802cbea@linaro.org/
Acked-by: MyungJoo Ham <myungjoo.ham@...sung.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---

LLM Generated explanations, may be completely bogus:

Now let me compile my comprehensive analysis:

## **BACKPORT RECOMMENDATION: YES (with critical caveat)**

### **Executive Summary**

This commit **SHOULD be backported** to stable kernel trees, **BUT it
MUST be backported together with its follow-up fix commit
92bac7d4de9c0** ("extcon: adc-jack: Cleanup wakeup source only if it was
enabled"). Backporting commit 78b6a991eb6c6 alone would fix a memory
leak but introduce a subtle correctness bug.

---

### **Detailed Technical Analysis**

#### **1. Nature of the Bug**

The commit fixes a **memory leak of wakeup_source structures** that
occurs when the adc-jack device is unbound:

**Root Cause:**
- In `adc_jack_probe()` (drivers/extcon/extcon-adc-jack.c:156-157), when
  `data->wakeup_source` is true, the driver calls
  `device_init_wakeup(&pdev->dev, 1)`
- This allocates a `wakeup_source` structure involving:
  - `kzalloc()` for the structure itself
  - `kstrdup_const()` for the name string
  - `ida_alloc()` for ID allocation
  - Registration in the global wakeup_sources list

**The Leak:**
- The original `adc_jack_remove()` function has NO corresponding cleanup
  call
- Without `device_init_wakeup(&pdev->dev, false)`, the allocated
  wakeup_source is never freed
- This memory leaks every time the device is unbound (manual unbind via
  sysfs, driver removal, module unload)

#### **2. The Fix (Commit 78b6a991eb6c6)**

**Code Change:**
```c
static void adc_jack_remove(struct platform_device *pdev)
{
    struct adc_jack_data *data = platform_get_drvdata(pdev);

+   device_init_wakeup(&pdev->dev, false);  // ← Added this line
    free_irq(data->irq, data);
    cancel_work_sync(&data->handler.work);
}
```

**What device_init_wakeup(dev, false) does:**
1. Calls `device_wakeup_disable(dev)` which:
   - Detaches the wakeup_source from the device
   - Calls `wakeup_source_unregister()` to remove it from the list
   - Calls `wakeup_source_destroy()` to free all allocated memory

2. Calls `device_set_wakeup_capable(dev, false)` to clear the capability
   flag

#### **3. Critical Issue: The Follow-up Fix is Required**

**Problem with 78b6a991eb6c6 alone:**
- The fix unconditionally calls `device_init_wakeup(&pdev->dev, false)`
- But probe only calls `device_init_wakeup(&pdev->dev, 1)` when
  `data->wakeup_source` is true
- Calling `device_init_wakeup(false)` when it was never initialized
  could:
  - Call `device_wakeup_disable()` on a NULL or uninitialized
    wakeup_source
  - While this might not crash (the function checks for NULL), it's
    technically incorrect behavior

**The Follow-up Fix (92bac7d4de9c0):**
Adds the conditional check that mirrors the probe logic:
```c
static void adc_jack_remove(struct platform_device *pdev)
{
    struct adc_jack_data *data = platform_get_drvdata(pdev);

- device_init_wakeup(&pdev->dev, false);
+   if (data->wakeup_source)
+       device_init_wakeup(&pdev->dev, false);
    free_irq(data->irq, data);
    cancel_work_sync(&data->handler.work);
}
```

This was reported by Christophe JAILLET 8 days after the original fix
(May 1 → May 9, 2025).

#### **4. Why Not Use devm_device_init_wakeup()?**

Other drivers in the same patch series (extcon-qcom-spmi-misc, extcon-
fsa9480) used the devm (device-managed) approach, which automatically
cleans up. However, adc-jack explicitly avoids this approach.

**Reason (from commit message):** "Do not use devm interface, because it
would change the order of cleanup."

**Cleanup Order Analysis:**
```
Current (with manual cleanup):
1. device_init_wakeup(false) - disable wakeup source
2. free_irq() - free interrupt
3. cancel_work_sync() - cancel pending work
4. (later) devm cleanup runs for other resources

With devm_device_init_wakeup:
1. free_irq() - free interrupt
2. cancel_work_sync() - cancel pending work
3. (later) devm cleanup runs, including wakeup disable

Problem: IRQ and work might still reference wakeup_source during cleanup
```

The manual approach ensures the wakeup source is disabled before other
related resources are freed, maintaining proper cleanup ordering.

#### **5. Pattern Analysis: Systematic Cleanup**

This is part of a **systematic cleanup series** by Krzysztof Kozlowski
(Linaro) fixing the same class of bug across multiple subsystems:

**Same Author, Same Pattern (partial list):**
- extcon: adc-jack, qcom-spmi-misc, fsa9480, axp288
- mfd: sprd-sc27xx, rt5033, max8925, max77705, max77541, max14577,
  as3722, 88pm886
- Bluetooth: btmtksdio, btmrvl_sdio
- iio: st_lsm6dsx, qcom-spmi-iadc, fxls8962af
- usb typec: tipd, tcpci
- power supply: gpio-charger, collie
- watchdog: stm32

This indicates a **project-wide audit** for this specific resource leak
pattern, lending credibility to the importance of the fix.

#### **6. Impact Assessment**

**Severity: Medium**
- Resource leak, but only triggered on device unbind
- Device unbind is relatively uncommon (manual unbind, rmmod, shutdown)
- Leak is small per occurrence (one wakeup_source structure ~100-200
  bytes)
- **But**: repeated bind/unbind cycles accumulate leaks
- **More important**: This is incorrect resource management that
  violates kernel coding practices

**Affected Users:**
- Users with ADC-based jack detection hardware (primarily Samsung
  devices)
- Systems that dynamically load/unload extcon modules
- Embedded systems with power management requirements
- kexec/kdump scenarios where driver cleanup matters

**Regression Risk: Very Low**
- Minimal, contained change (1-2 lines)
- Only affects remove path
- Mirrors the probe logic symmetrically
- Has been in mainline with no reported issues

#### **7. Stable Tree Backporting Criteria Analysis**

✅ **Fixes an important bug:** Resource leak violating kernel resource
management rules

✅ **Small and contained:** 1-line fix + 1-line follow-up (total 2 lines
across 2 commits)

✅ **Low regression risk:** Remove path only, symmetric to probe, minimal
code change

✅ **No architectural changes:** Pure resource management fix

✅ **Confined to subsystem:** Only affects extcon adc-jack driver

✅ **Clear and obvious fix:** The fix is straightforward and correct

⚠️ **Requires follow-up commit:** Must include 92bac7d4de9c0 for
correctness

❌ **No explicit stable tag:** Commit message lacks "Cc:
stable@...r.kernel.org" tag

#### **8. Comparison with Stable Tree Precedents**

Looking at similar commits in this cleanup series, many include explicit
stable tags. However, the absence of a stable tag doesn't preclude
backporting when the fix meets other criteria.

**Similar fixes that were backported (based on pattern):**
- Memory leaks on device unbind are consistently considered backport-
  worthy
- Resource management fixes are high priority for stable trees
- Small, contained fixes with clear benefits are typically backported

---

### **RECOMMENDATION**

**YES - This commit should be backported to stable kernel trees.**

**Critical Requirements:**
1. **MUST backport both commits together:**
   - 78b6a991eb6c6 ("extcon: adc-jack: Fix wakeup source leaks on device
     unbind")
   - 92bac7d4de9c0 ("extcon: adc-jack: Cleanup wakeup source only if it
     was enabled")

2. **Suggested stable trees:** All active stable trees where the adc-
   jack driver exists with wakeup_source support

3. **Rationale Summary:**
   - Fixes genuine resource leak
   - Part of systematic kernel-wide cleanup
   - Low risk, high correctness value
   - Minimal code change
   - Both commits required for complete, correct fix

**Implementation Note:** When submitting to stable, reference both
commits and explain that 92bac7d4de9c0 is a necessary correction to
78b6a991eb6c6.

 drivers/extcon/extcon-adc-jack.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/extcon/extcon-adc-jack.c b/drivers/extcon/extcon-adc-jack.c
index 46c40d85c2ac8..557930394abd2 100644
--- a/drivers/extcon/extcon-adc-jack.c
+++ b/drivers/extcon/extcon-adc-jack.c
@@ -164,6 +164,7 @@ static void adc_jack_remove(struct platform_device *pdev)
 {
 	struct adc_jack_data *data = platform_get_drvdata(pdev);
 
+	device_init_wakeup(&pdev->dev, false);
 	free_irq(data->irq, data);
 	cancel_work_sync(&data->handler.work);
 }
-- 
2.51.0

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