Messages in this thread | | | From | Xiongwei Song <> | Date | Mon, 12 Jul 2021 17:21:43 +0800 | Subject | Re: [RFC PATCH v1 1/3] locking/lockdep: Fix false warning of check_wait_context() |
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On Mon, Jul 12, 2021 at 4:52 PM Boqun Feng <boqun.feng@gmail.com> wrote: > > On Mon, Jul 12, 2021 at 04:18:36PM +0800, Xiongwei Song wrote: > > On Mon, Jul 12, 2021 at 12:43 AM Waiman Long <llong@redhat.com> wrote: > > > > > > On 7/11/21 10:14 AM, Xiongwei Song wrote: > > > > From: Xiongwei Song <sxwjean@gmail.com> > > > > > > > > We now always get a "Invalid wait context" warning with > > > > CONFIG_PROVE_RAW_LOCK_NESTING=y, see the full warning below: > > > > > > > > [ 0.705900] ============================= > > > > [ 0.706002] [ BUG: Invalid wait context ] > > > > [ 0.706180] 5.13.0+ #4 Not tainted > > > > [ 0.706349] ----------------------------- > > > > > > I believe the purpose of CONFIG_PROVE_RAW_LOCK_NESTING is experimental > > > and it is turned off by default. Turning it on can cause problem as > > > shown in your lockdep splat. Limiting it to just PREEMPT_RT will defeat > > > its purpose to find potential spinlock nesting problem in non-PREEMPT_RT > > > kernel. > > As far as I know, a spinlock can nest another spinlock. In > > non-PREEMPT_RT kernel > > spin_lock and raw_spin_lock are same , so here acquiring a spin_lock in hardirq > > context is acceptable, the warning is not needed. My knowledge on this > > is not enough, > > Will dig into this. > > > > You may find this useful: https://lwn.net/Articles/146861/ ;-) > > The thing is that most of the irq handlers will run in process contexts > in PREEMPT_RT kernel (threaded irq), while the rest continues to run in > hardirq contexts. spinlock_t is allowed int threaded irqs but not in > hardirq contexts for PREEMPT_RT, because spinlock_t will become > sleeplable locks. Exactly. I think I have known why the fix is incorrect.
Regards, Xiongwei > > Regards, > Boqun > > > > The point is to fix the issue found, > > Agree. I thought there was a spinlock usage issue, but by checking > > deactivate_slab context, > > looks like the spinlock usage is well. Maybe I'm missing something? > > > > > not hiding it from appearing. > > I'm not trying to hiding it, according to the code context, the fix is > > reasonable from my point of > > view. Let me check again. > > > > Thank you for the comments. > > > > Regards, > > Xiongwei > > > > > > Cheers, > > > Longman > > >
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