[PATCH v5 0/5] phy: qcom: Fix possible NULL-deref and runtime PM race conditions

* [PATCH v5 0/5] phy: qcom: Fix possible NULL-deref and runtime PM race conditions
@ 2026-07-21 13:05 ` Loic Poulain
  0 siblings, 0 replies; 18+ messages in thread
From: Loic Poulain @ 2026-07-21 13:05 UTC (permalink / raw)
  To: Vinod Koul, Neil Armstrong, Dmitry Baryshkov, Wesley Cheng
  Cc: linux-arm-msm, linux-phy, linux-kernel, Dmitry Baryshkov,
	Abel Vesa, Konrad Dybcio, Loic Poulain

Address potential NULL pointer dereferences and race conditions related
to runtime PM in several Qualcomm PHY drivers. In all cases, enabling
runtime PM before the PHY instance is fully initialized can lead to
crashes during early runtime suspend callbacks.

- Attach driver data before enabling runtime PM.
- Introduce initialization flags where needed to avoid dereferencing
uninitialized pointers.
- Reorder pm_runtime_enable() and pm_runtime_forbid() calls to prevent
unnecessary suspend/resume cycles during driver probe.
- Use devres-managed PM runtime helpers for proper cleanup.

Why it happens?

The PHY is a supplier of the USB device. A USB device cannot be probed
until all its suppliers are ready. As long as the PHY is not ready, the
device core keeps retrying the probe, which fails with -EPROBE_DEFER.

At some point the PHY probe finally runs, but the device core may still be
attempting to probe the USB device concurrently.

Inside __driver_probe_device(), we have:

    ret = really_probe(dev, drv);
    pm_request_idle(dev);

    if (dev->parent)
        pm_runtime_put(dev->parent);

    pm_runtime_put_suppliers(dev);
    return ret;

This means that whenever a USB probe attempt completes, whether with an
error or not, its suppliers are released via pm_runtime_put_suppliers().
Releasing suppliers may in turn trigger a runtime suspend.

In our case, since the PHY is a supplier of the USB device, the USB core
keeps 'looping' in __driver_probe_device() returning -EPROBE_DEFER until
the PHY becomes ready. As a result, pm_runtime_put_suppliers() may run
concurrently with the PHY's probe function. If this happens after
runtime PM has been enabled for the PHY, but before the driver has
forbidden suspend or taken a PM reference, the PHY may end up being
runtime-suspended 'unexpectedly'

---
Changes in v5:
- Re-introduce phy: qcom: qmp-usb-legacy: Fix possible NULL-deref (sashiko)
- Link to v4: https://lore.kernel.org/r/20260720-qcom-usb-phy-fix-null-v4-0-4d2a0f06d53a@oss.qualcomm.com

Changes in V4:
- Instead of moving pm/forbid, increment the pm usage counter before
  enabling runtime pm and decrement it after the PHY has been created. (Johan)
- Drop now unnecessary dev_set_drvdata() move in snps-femto-v2
- Drop 4/5 (qmp-usb-legacy: Prevent unnecessary PM runtime suspend at boot)
  which is not required anymore. 
- Rebase
- Link to v3: https://lore.kernel.org/all/20260205160240.748371-1-loic.poulain@oss.qualcomm.com/

Changes in v3:
Rebase on next and remove 2/6 (obsolete)

Changes in v2:
Split patches 2/4 and 3/4 so that the null‑pointer dereference fix and
the runtime‑PM enable/forbid reordering are logically separated.

Loic Poulain (4):
  phy: qcom: qmp-combo: Prevent unnecessary PM runtime suspend at boot
  phy: qcom: qmp-usbc: Prevent unnecessary PM runtime suspend at boot
  phy: qcom: qmp-usb-legacy: Fix possible NULL-deref on early runtime
    suspend
  phy: qcom: snps-femto-v2: Fix possible NULL-deref on early runtime
    suspend

 drivers/phy/qualcomm/phy-qcom-qmp-combo.c     | 10 ++++-----
 .../phy/qualcomm/phy-qcom-qmp-usb-legacy.c    | 21 ++++++++++++-------
 drivers/phy/qualcomm/phy-qcom-qmp-usbc.c      | 10 ++++-----
 drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c | 15 ++++++-------
 4 files changed, 32 insertions(+), 24 deletions(-)

--
2.34.1

To: Vinod Koul <vkoul@kernel.org>
To: Neil Armstrong <neil.armstrong@linaro.org>
To: Dmitry Baryshkov <lumag@kernel.org>
To: Wesley Cheng <quic_wcheng@quicinc.com>
Cc: linux-arm-msm@vger.kernel.org
Cc: linux-phy@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

---
Loic Poulain (5):
      phy: qcom: qmp-combo: Prevent unnecessary PM runtime suspend at boot
      phy: qcom: qmp-usbc: Prevent unnecessary PM runtime suspend at boot
      phy: qcom: qmp-usb-legacy: Fix possible NULL-deref on early runtime suspend
      phy: qcom: qmp-usb-legacy: Prevent unnecessary PM runtime suspend at boot
      phy: qcom: snps-femto-v2: Fix possible NULL-deref on early runtime suspend

 drivers/phy/qualcomm/phy-qcom-qmp-combo.c      | 19 ++++++++++++-----
 drivers/phy/qualcomm/phy-qcom-qmp-usb-legacy.c | 28 +++++++++++++++++++++-----
 drivers/phy/qualcomm/phy-qcom-qmp-usbc.c       | 18 +++++++++++++----
 drivers/phy/qualcomm/phy-qcom-snps-femto-v2.c  | 17 +++++++++++++---
 4 files changed, 65 insertions(+), 17 deletions(-)
---
base-commit: 910b828b22b7b91054b3bd4be676a017444b0e00
change-id: 20260720-qcom-usb-phy-fix-null-ff097f56d1e4

Best regards,
-- 
Loic Poulain <loic.poulain@oss.qualcomm.com>

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