On Tue, 2019-09-17 at 16:50 +0200, Sebastian Andrzej Siewior wrote: > On 2019-09-17 09:36:22 [-0500], Scott Wood wrote: > > > On non-RT you can (but should not) use the counter part of the > > > function > > > in random order like: > > > local_bh_disable(); > > > local_irq_disable(); > > > local_bh_enable(); > > > local_irq_enable(); > > > > Actually even non-RT will assert if you do local_bh_enable() with IRQs > > disabled -- but the other combinations do work, and are used some places > > via > > spinlocks. If they are used via direct calls to preempt_disable() or > > local_irq_disable() (or via raw spinlocks), then that will not go away > > on RT > > and we'll have a problem. > > lockdep_assert_irqs_enabled() is a nop with CONFIG_PROVE_LOCKING=N and > RT breaks either way. Right, I meant a non-RT kernel with debug checks enabled. > > > Since you _can_ use it in random order Paul wants to test that the > > > random use of those function does not break RCU in any way. Since they > > > can not be used on RT in random order it has been agreed that we keep > > > the test for !RT but disable it on RT. > > > > For now, yes. Long term it would be good to keep track of when > > preemption/irqs would be disabled on RT, even when running a non-RT > > debug > > kernel, and assert when bad things are done with it (assuming an RT- > > capable > > arch). Besides detecting these fairly unusual patterns, it could also > > detect earlier the much more common problem of nesting a non-raw > > spinlock > > inside a raw spinlock or other RT-atomic context. > > you will be surprised but we have patches for that. We need first get > rid of other "false positives" before plugging this in. Nice! Are the "false positives" real issues from components that are currently blacklisted on RT, or something different? -Scott
