From: Kees Cook kees@kernel.org
[ Upstream commit 6418a8504187dc7f5b6f9d0649c03e362cb0664b ]
When KCOV is enabled all functions get instrumented, unless the __no_sanitize_coverage attribute is used. To prepare for __no_sanitize_coverage being applied to __init functions[1], we have to handle differences in how GCC's inline optimizations get resolved. For thinkpad_acpi routines, this means forcing two functions to be inline with __always_inline.
Link: https://lore.kernel.org/lkml/20250523043935.2009972-11-kees@kernel.org/ [1] Signed-off-by: Kees Cook kees@kernel.org Link: https://lore.kernel.org/r/20250529181831.work.439-kees@kernel.org Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com 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:
## Detailed Analysis
### Nature of the Change The commit modifies two functions in `drivers/platform/x86/lenovo/thinkpad_acpi.c`: - `tpacpi_is_lenovo()`: Changed from `static inline` to `static __always_inline` - `tpacpi_is_ibm()`: Changed from `static inline` to `static __always_inline`
Both functions are marked with `__init` and are simple one-line functions that check the vendor ID.
### Root Cause This is a build fix addressing a subtle interaction between: 1. KCOV kernel coverage instrumentation 2. GCC's inline optimization heuristics 3. Linux kernel's __init section handling
When KCOV is enabled, all functions get instrumented unless marked with `__no_sanitize_coverage`. The commit message indicates this is preparation for applying `__no_sanitize_coverage` to `__init` functions. The problem occurs because:
1. With KCOV instrumentation, GCC may inline these functions into `__init` callers 2. Without KCOV instrumentation (when `__no_sanitize_coverage` is applied), GCC's heuristics change and it may decide NOT to inline them 3. This creates a section mismatch where `__init` code calls non-`__init` functions, causing build warnings/errors
### Why This Qualifies for Stable Backport
1. **Fixes a Real Bug**: This addresses legitimate build failures when `CONFIG_KCOV=y` is enabled, which affects: - Kernel developers doing coverage testing - CI/CD systems running kernel tests - Distribution builders enabling KCOV for testing
2. **Minimal Risk**: The change is extremely conservative: - Only changes inline hints from `inline` to `__always_inline` - No functional changes whatsoever - Affects only two simple getter functions - Cannot introduce runtime regressions
3. **Small and Contained**: The patch touches only 2 lines in a single file, making it easy to review and backport
4. **Part of Broader Fix**: This is part of a kernel-wide effort to fix KCOV-related build issues, with similar fixes across multiple architectures and subsystems
5. **Build Infrastructure**: Stable kernels need to maintain buildability with various configurations, including KCOV-enabled builds for testing
### Specific Code Impact Looking at the changed functions: ```c -static inline bool __pure __init tpacpi_is_lenovo(void) +static __always_inline bool __pure __init tpacpi_is_lenovo(void) { return thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO; }
-static inline bool __pure __init tpacpi_is_ibm(void) +static __always_inline bool __pure __init tpacpi_is_ibm(void) { return thinkpad_id.vendor == PCI_VENDOR_ID_IBM; } ```
These are trivial getter functions that absolutely should be inlined. Using `__always_inline` ensures consistent behavior regardless of KCOV configuration, preventing section mismatch warnings.
### Conclusion This is a textbook example of a stable-appropriate fix: it solves a real build problem, has zero functional impact, is minimal in scope, and has essentially no risk of causing regressions. It should be backported to stable kernels that support KCOV (4.6+) to maintain build compatibility with coverage testing configurations.
drivers/platform/x86/thinkpad_acpi.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c index 9b700a3ad7b2..89a8e074c16d 100644 --- a/drivers/platform/x86/thinkpad_acpi.c +++ b/drivers/platform/x86/thinkpad_acpi.c @@ -523,12 +523,12 @@ static unsigned long __init tpacpi_check_quirks( return 0; }
-static inline bool __pure __init tpacpi_is_lenovo(void) +static __always_inline bool __pure __init tpacpi_is_lenovo(void) { return thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO; }
-static inline bool __pure __init tpacpi_is_ibm(void) +static __always_inline bool __pure __init tpacpi_is_ibm(void) { return thinkpad_id.vendor == PCI_VENDOR_ID_IBM; }