CONFIG_TASKS_TRACE_RCU_NO_MB: Override RCU Tasks Trace inclusion of read-side memory barriers

General informations

The Linux kernel configuration item CONFIG_TASKS_TRACE_RCU_NO_MB:

• prompt: Override RCU Tasks Trace inclusion of read-side memory barriers
• type: bool
• depends on: CONFIG_RCU_EXPERT && CONFIG_TASKS_TRACE_RCU
• defined in kernel/rcu/Kconfig
• found in Linux kernels: 7.0-rc+HEAD

Help text

This option prevents the use of read-side memory barriers in rcu_read_lock_tasks_trace() and rcu_read_unlock_tasks_trace() even in kernels built with ARCH_WANTS_NO_INSTR=n, that is, in kernels that do not have noinstr set up in entry/exit code. By setting this option, you are promising to carefully review use of ftrace, BPF, and friends to ensure that no tracing operation is attached to a function that runs in that portion of the entry/exit code that RCU does not watch, that is, where rcu_is_watching() returns false. Alternatively, you might choose to never remove traces except by rebooting.

Those wishing to disable read-side memory barriers for an entire architecture can select this Kconfig option, hence the polarity.

Say Y here if you need speed and will review use of tracing. Say N here for certain esoteric testing of RCU itself. Take the default if you are unsure.

Hardware

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