diff options
| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2025-09-04 16:25:25 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2025-09-17 16:25:41 +0200 |
| commit | 3253cb49cbad4772389d6ef55be75db1f97da910 (patch) | |
| tree | 2c628c0f0f9dd8177184507a35c48f5b83a19912 /kernel/Kconfig.preempt | |
| parent | softirq: Provide a handshake for canceling tasklets via polling (diff) | |
| download | linux-3253cb49cbad4772389d6ef55be75db1f97da910.tar.gz linux-3253cb49cbad4772389d6ef55be75db1f97da910.zip | |
softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT
softirqs are preemptible on PREEMPT_RT. There is synchronisation between
individual sections which disable bottom halves. This in turn means that
a forced threaded interrupt cannot preempt another forced threaded
interrupt. Instead it will PI-boost the other handler and wait for its
completion.
This is required because code within a softirq section is assumed to be
non-preemptible and may expect exclusive access to per-CPU resources
such as variables or pinned timers.
Code with such expectation has been identified and updated to use
local_lock_nested_bh() for locking of the per-CPU resource. This means the
softirq lock can be removed.
Disable the softirq synchronization, but add a new config switch
CONFIG_PREEMPT_RT_NEEDS_BH_LOCK which allows to re-enable the synchronized
behavior in case that there are issues, which haven't been detected yet.
The softirq_ctrl.cnt accounting remains to let the NOHZ code know if
softirqs are currently handled.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/Kconfig.preempt')
| -rw-r--r-- | kernel/Kconfig.preempt | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 54ea59ff8fbe..da326800c1c9 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -103,6 +103,19 @@ config PREEMPT_RT Select this if you are building a kernel for systems which require real-time guarantees. +config PREEMPT_RT_NEEDS_BH_LOCK + bool "Enforce softirq synchronisation on PREEMPT_RT" + depends on PREEMPT_RT + help + Enforce synchronisation across the softirqs context. On PREEMPT_RT + the softirq is preemptible. This enforces the same per-CPU BLK + semantic non-PREEMPT_RT builds have. This should not be needed + because per-CPU locks were added to avoid the per-CPU BKL. + + This switch provides the old behaviour for testing reasons. Select + this if you suspect an error with preemptible softirq and want test + the old synchronized behaviour. + config PREEMPT_COUNT bool |