[PATCH AUTOSEL 6.17-6.12] ACPI: sysfs: Use ACPI_FREE() for freeing an ACPI object

[Sasha Levin <sashal@kernel.org>]

From: Kaushlendra Kumar <kaushlendra.kumar@intel.com>

[ Upstream commit 149139ddcb99583fdec8d1eaf7dada41e5896101 ]

Since str_obj is allocated by ACPICA in acpi_evaluate_object_typed(),
it should be free with ACPI_FREE() rather than with kfree(), so use
the former instead of the latter for freeing it.

Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Link: https://patch.msgid.link/20250822061946.472594-1-kaushlendra.kumar@intel.com
[ rjw: Subject and changelog rewrite ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my comprehensive investigation of this commit and the ACPICA
memory management infrastructure, here is my analysis:

## Analysis Summary

**Backport Status: YES** (with low priority - code correctness/cleanup
fix)

## Detailed Technical Analysis

### What This Commit Fixes

This commit changes one line in `drivers/acpi/device_sysfs.c:467`:
- **Before**: `kfree(str_obj);`
- **After**: `ACPI_FREE(str_obj);`

The `str_obj` is allocated by `acpi_evaluate_object_typed()` at line
447, which uses ACPICA's internal allocation mechanism.

### The Core Issue

In the Linux kernel's ACPICA implementation, there are two possible
memory management paths:

1. **Normal Linux kernel builds** (ACPI_DBG_TRACK_ALLOCATIONS disabled):
   - `ACPI_FREE()` expands to `acpi_os_free()`
   - `acpi_os_free()` is implemented as `kfree()` (see
     `include/acpi/platform/aclinuxex.h:62-65`)
   - **Functionally equivalent**: `ACPI_FREE()` == `kfree()`

2. **ACPI debugging builds** (ACPI_DBG_TRACK_ALLOCATIONS enabled, only
   for acpi_exec utility):
   - `ACPI_FREE()` expands to `acpi_ut_free_and_track()`
   - This tracks allocations for memory leak detection
   - Using `kfree()` directly **breaks allocation tracking**

### Is This a Real Bug?

**In production Linux kernels: NO** - The code is functionally correct
because `ACPI_FREE()` and `kfree()` are equivalent.

**For ACPICA coding standards: YES** - Memory allocated by ACPICA
functions (like `acpi_evaluate_object_typed()`) should be freed using
`ACPI_FREE()` to maintain consistency and support debugging builds.

### Pattern of Similar Fixes

Multiple commits have addressed this same issue:
- `c00901e98b1e9`: "ACPI: pfr_update: use ACPI_FREE() to free
  acpi_object"
- `ae3075b54fa8d`: "ACPI: pfr_telemetry: use ACPI_FREE() to free
  acpi_object"
- `252f006676d1b`: "net: wwan: iosm: use ACPI_FREE() but not kfree()"

All cite the same rationale: "we need to track the allocation of
acpi_object when ACPI_DBG_TRACK_ALLOCATIONS enabled"

### Why This Should Be Backported

1. **Code correctness**: Follows ACPICA conventions -
   allocation/deallocation should use matching functions
2. **Extremely low risk**: In the kernel, this is a no-op change since
   the functions are equivalent
3. **Consistency**: Part of a wider effort to fix this pattern across
   the kernel
4. **Debugging support**: Enables proper memory leak detection in ACPICA
   debugging tools
5. **Small, contained change**: Single line modification with no side
   effects
6. **Already backported**: This commit is itself a stable backport
   (upstream: `149139ddcb99`)

### Why This Has Low Priority

1. **No user-visible impact**: Does not fix crashes, data corruption, or
   functional bugs
2. **No security implications**: Not exploitable or security-related
3. **Cleanup/style fix**: Primarily about code correctness rather than
   fixing broken functionality

### Conclusion

This is a **low-priority correctness fix** suitable for backporting.
While it doesn't fix a critical bug affecting users, it:
- Maintains proper ACPICA coding standards
- Has zero risk of regression (equivalent functions)
- Aligns with a consistent pattern of similar fixes in stable trees
- Improves code maintainability and debugging capability

The commit follows stable kernel rules by being a small, safe
improvement with clear benefits and no downsides.

 drivers/acpi/device_sysfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
index 3961fc47152c0..cd199fbe4dc90 100644
--- a/drivers/acpi/device_sysfs.c
+++ b/drivers/acpi/device_sysfs.c
@@ -464,7 +464,7 @@ static ssize_t description_show(struct device *dev,
 
 	buf[result++] = '\n';
 
-	kfree(str_obj);
+	ACPI_FREE(str_obj);
 
 	return result;
 }
-- 
2.51.0