Hello! This RFC series provides the second version of an NMI-safe SRCU reader API in the guise of srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe(). A given srcu_struct structure must use either the traditional srcu_read_lock() and srcu_read_unlock() API or the new _nmisafe() API: Mixing and matching is not permitted. So much so that kernels built with CONFIG_PROVE_RCU=y will complain if you try it. The reason for this restriction is that I have yet to find a use case that is not a accident waiting to happen. And if free intermixing were permitted, it is pretty much a given that someone somewhere will get confused and use srcu_read_lock_nmisafe() within NMI handlers and srcu_read_lock() elsewhere, which will not (repeat, NOT) provide NMI safety. I do not expect to push this into the v6.1 merge window. However, if the printk() series that needs it goes in, then I will push it as a fix for the resulting regression. The series is as follows: 1. Convert ->srcu_lock_count and ->srcu_unlock_count to atomic. 2. Create an srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe(). 3. Check for consistent per-CPU per-srcu_struct NMI safety. 4. Check for consistent global per-srcu_struct NMI safety. 5. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. 6. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. 7. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. 8. Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option. Changes since v1 RFC: 1. Added enabling patches for arm64, loongarch, s390, and x86. These have what appear to me to be NMI-safe this_cpu_inc() implementations. 2. Fix a build error on !SMP kernels built without SRCU. 3. Fix a build error on !SMP kernels. Thanx, Paul ------------------------------------------------------------------------ b/arch/arm64/Kconfig | 1 b/arch/loongarch/Kconfig | 1 b/arch/s390/Kconfig | 1 b/arch/x86/Kconfig | 1 b/include/linux/srcu.h | 39 +++++++++++++++++++++ b/include/linux/srcutiny.h | 11 ++++++ b/include/linux/srcutree.h | 4 +- b/kernel/rcu/Kconfig | 3 + b/kernel/rcu/rcutorture.c | 11 ++++-- b/kernel/rcu/srcutree.c | 24 ++++++------- include/linux/srcu.h | 4 +- include/linux/srcutiny.h | 4 +- include/linux/srcutree.h | 12 +++++- kernel/rcu/srcutree.c | 82 +++++++++++++++++++++++++++++++++++++++------ 14 files changed, 166 insertions(+), 32 deletions(-)
