Hi Greg,
On 8/3/25 6:30 오전, Greg Kroah-Hartman wrote:
On Sat, Aug 02, 2025 at 02:26:49PM +0000, Yunseong Kim wrote:
The KCOV subsystem currently utilizes standard spinlock_t and local_lock_t for synchronization. In PREEMPT_RT configurations, these locks can be implemented via rtmutexes and may therefore sleep. This behavior is problematic as kcov locks are sometimes used in atomic contexts or protect data accessed during critical instrumentation paths where sleeping is not permissible.
Address these issues to make kcov PREEMPT_RT friendly:
Convert kcov->lock and kcov_remote_lock from spinlock_t to raw_spinlock_t. This ensures they remain true, non-sleeping spinlocks even on PREEMPT_RT kernels.
Refactor the KCOV_REMOTE_ENABLE path to move memory allocations out of the critical section. All necessary struct kcov_remote structures are now pre-allocated individually in kcov_ioctl() using GFP_KERNEL (allowing sleep) before acquiring the raw spinlocks.
Modify the ioctl handling logic to utilize these pre-allocated structures within the critical section. kcov_remote_add() is modified to accept a pre-allocated structure instead of allocating one internally.
Remove the local_lock_t protection for kcov_percpu_data in kcov_remote_start/stop(). Since local_lock_t can also sleep under RT, and the required protection is against local interrupts when accessing per-CPU data, it is replaced with explicit local_irq_save/restore().
why isn't this 4 different patches?
Thank you for your feedback on the patch. I’ll split it into four separate patches for v3 to improve clarity.
Best regards, Yunseong Kim