From: "Rafael J. Wysocki" rafael.j.wysocki@intel.com
[ Upstream commit 89d9cec3b1e9c49bae9375a2db6dc49bc7468af0 ]
Clear power.needs_force_resume in pm_runtime_reinit() in case it has been set by pm_runtime_force_suspend() invoked from a driver remove callback.
Suggested-by: Ulf Hansson ulf.hansson@linaro.org Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Reviewed-by: Ulf Hansson ulf.hansson@linaro.org Link: https://patch.msgid.link/9495163.CDJkKcVGEf@rjwysocki.net Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**Backport Status: YES**
This commit is a clear bugfix that should be backported to stable kernel trees for the following reasons:
1. **It fixes a real bug**: The commit addresses a specific issue where `power.needs_force_resume` flag is not cleared in `pm_runtime_reinit()` when a device is removed. If a driver calls `pm_runtime_force_suspend()` from its remove callback (which sets `needs_force_resume = 1`), this flag remains set even after the device is removed and potentially re-probed.
2. **The fix is minimal and contained**: The change adds just 5 lines of code (including comments) to clear a single flag. The modification is: ```c dev->power.needs_force_resume = false; ``` This is a very low-risk change that only affects the specific condition being fixed.
3. **It prevents state leakage**: Looking at the code flow: - `pm_runtime_force_suspend()` sets `dev->power.needs_force_resume = 1` (line in runtime.c) - When a driver is removed, `pm_runtime_remove()` calls `pm_runtime_reinit()` - Without this fix, if the device is re-probed, it would still have `needs_force_resume = 1` from the previous instance - This could lead to incorrect PM runtime behavior where `pm_runtime_force_resume()` would incorrectly think it needs to resume a device that was never suspended in the current probe cycle
4. **Related to previous stable fixes**: The git history shows a previous commit `c745253e2a69` ("PM: runtime: Fix unpaired parent child_count for force_resume") was already marked for stable (4.16+), indicating that issues with the `needs_force_resume` flag have been problematic enough to warrant stable backports.
5. **Clear bug scenario**: The commit message describes a specific scenario where this happens - when `pm_runtime_force_suspend()` is called from a driver remove callback. This is a legitimate use case where drivers want to ensure devices are suspended before removal.
6. **No architectural changes**: This is purely a bugfix that clears a flag that should have been cleared during reinitialization. It doesn't introduce new features or change any APIs.
The fix ensures proper PM runtime state management across device removal and re-probing cycles, which is important for system stability and correct power management behavior.
drivers/base/power/runtime.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index 0d43bf5b6cec..d89439e3605a 100644 --- a/drivers/base/power/runtime.c +++ b/drivers/base/power/runtime.c @@ -1754,6 +1754,11 @@ void pm_runtime_reinit(struct device *dev) pm_runtime_put(dev->parent); } } + /* + * Clear power.needs_force_resume in case it has been set by + * pm_runtime_force_suspend() invoked from a driver remove callback. + */ + dev->power.needs_force_resume = false; }
/**