From: Ulf Hansson ulf.hansson@linaro.org
[ Upstream commit 47a255f7d2eabee06cfbf5b1c2379749442fd01d ]
In the error path of sd_set_power_mode() we don't update host->power_mode, which could lead to an imbalance of the runtime PM usage count. Fix this by always updating host->power_mode.
Reviewed-by: Avri Altman avri.altman@sandisk.com Signed-off-by: Ulf Hansson ulf.hansson@linaro.org Acked-by: Ricky Wu ricky_wu@realtek.com Link: https://lore.kernel.org/r/20250610111633.504366-2-ulf.hansson@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**YES**
This commit should be backported to stable kernel trees. Here's my extensive analysis:
## Bug Analysis
The commit fixes a **runtime PM reference counting bug** in the `sd_set_power_mode()` function. The issue is in the error handling path:
### Original Code Problem: ```c if (power_mode == MMC_POWER_OFF) { err = sd_power_off(host); pm_runtime_put_noidle(sdmmc_dev(host)); } else { pm_runtime_get_noresume(sdmmc_dev(host)); err = sd_power_on(host); }
if (!err) host->power_mode = power_mode; // Only updated on success ```
### The Bug: 1. When transitioning to `MMC_POWER_OFF`, the code calls `pm_runtime_put_noidle()` **regardless** of whether `sd_power_off()` succeeded 2. When transitioning to `MMC_POWER_ON`, the code calls `pm_runtime_get_noresume()` **before** calling `sd_power_on()` 3. However, `host->power_mode` is only updated if there's no error
This creates a **runtime PM reference count imbalance** because: - If `sd_power_off()` fails, the runtime PM reference is still decremented, but `host->power_mode` remains at its previous value (likely `MMC_POWER_ON`) - If `sd_power_on()` fails, the runtime PM reference is still incremented, but `host->power_mode` remains at its previous value (likely `MMC_POWER_OFF`) - The early return check `if (power_mode == host->power_mode)` at the beginning of the function will prevent future attempts to fix the power state, leaving the runtime PM count permanently imbalanced
## Why This Is Suitable for Stable:
1. **Fixes a real bug**: Runtime PM reference count imbalances can lead to: - Device staying powered when it should be suspended - Device being suspended when it should be active - Power management failures - Potential system hangs or crashes
2. **Minimal change**: The fix is a simple one-liner that always updates `host->power_mode` regardless of error status
3. **Low regression risk**: - The change doesn't introduce new functionality - It doesn't alter the control flow - It simply ensures state consistency
4. **Clear bug fix**: This is not a feature addition or optimization - it's fixing incorrect error handling that violates runtime PM rules
5. **Affects users**: This bug can manifest in real-world scenarios when SD card power operations fail, particularly with flaky hardware or during system stress
6. **Subsystem contained**: The fix is limited to a single MMC host driver and doesn't affect core kernel infrastructure
The commit follows stable kernel rules by being a minimal, targeted fix for a real bug that can affect system stability and power management.
drivers/mmc/host/rtsx_usb_sdmmc.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c index d229c2b83ea9..8c35cb85a9c0 100644 --- a/drivers/mmc/host/rtsx_usb_sdmmc.c +++ b/drivers/mmc/host/rtsx_usb_sdmmc.c @@ -1029,9 +1029,7 @@ static int sd_set_power_mode(struct rtsx_usb_sdmmc *host, err = sd_power_on(host); }
- if (!err) - host->power_mode = power_mode; - + host->power_mode = power_mode; return err; }