Messages in this thread | | | Subject | Re: [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred_qs() | From | Lai Jiangshan <> | Date | Tue, 12 Nov 2019 09:28:37 +0800 |
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On 2019/11/11 10:32 下午, Paul E. McKenney wrote: > On Mon, Nov 04, 2019 at 11:19:11PM -0800, Paul E. McKenney wrote: >> On Tue, Nov 05, 2019 at 10:09:15AM +0800, Lai Jiangshan wrote: >>> On 2019/11/4 10:55 下午, Paul E. McKenney wrote: >>>> On Sun, Nov 03, 2019 at 01:01:21PM +0800, Lai Jiangshan wrote: >>>>> >>>>> >>>>> On 2019/11/3 10:01 上午, Boqun Feng wrote: >>>>>> Hi Jiangshan, >>>>>> >>>>>> >>>>>> I haven't checked the correctness of this patch carefully, but.. >>>>>> >>>>>> >>>>>> On Sat, Nov 02, 2019 at 12:45:54PM +0000, Lai Jiangshan wrote: >>>>>>> Don't need to set ->rcu_read_lock_nesting negative, irq-protected >>>>>>> rcu_preempt_deferred_qs_irqrestore() doesn't expect >>>>>>> ->rcu_read_lock_nesting to be negative to work, it even >>>>>>> doesn't access to ->rcu_read_lock_nesting any more. >>>>>> >>>>>> rcu_preempt_deferred_qs_irqrestore() will report RCU qs, and may >>>>>> eventually call swake_up() or its friends to wake up, say, the gp >>>>>> kthread, and the wake up functions could go into the scheduler code >>>>>> path which might have RCU read-side critical section in it, IOW, >>>>>> accessing ->rcu_read_lock_nesting. >>>>> >>>>> Sure, thank you for pointing it out. >>>>> >>>>> I should rewrite the changelog in next round. Like this: >>>>> >>>>> rcu: cleanup rcu_preempt_deferred_qs() >>>>> >>>>> IRQ-protected rcu_preempt_deferred_qs_irqrestore() itself doesn't >>>>> expect ->rcu_read_lock_nesting to be negative to work. >>>>> >>>>> There might be RCU read-side critical section in it (from wakeup() >>>>> or so), 1711d15bf5ef(rcu: Clear ->rcu_read_unlock_special only once) >>>>> will ensure that ->rcu_read_unlock_special is zero and these RCU >>>>> read-side critical sections will not call rcu_read_unlock_special(). >>>>> >>>>> Thanks >>>>> Lai >>>>> >>>>> === >>>>> PS: Were 1711d15bf5ef(rcu: Clear ->rcu_read_unlock_special only once) >>>>> not applied earlier, it will be protected by previous patch (patch1) >>>>> in this series >>>>> "rcu: use preempt_count to test whether scheduler locks is held" >>>>> when rcu_read_unlock_special() is called. >>>> >>>> This one in -rcu, you mean? >>>> >>>> 5c5d9065e4eb ("rcu: Clear ->rcu_read_unlock_special only once") >>> >>> Yes, but the commit ID is floating in the tree. >> >> Indeed, that part of -rcu is subject to rebase, and will continue >> to be until about v5.5-rc5 or thereabouts. >> >> https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html >> >> My testing of your full stack should be complete by this coming Sunday >> morning, Pacific Time. > > And you will be happy to hear that it ran the full time without errors. > > Good show!!! > > My next step is to look much more carefully at the remaining patches, > checking my first impressions. This will take a few days. >
Hi, All
I'm still asking for more comments.
By now, I have received some precious comments, mainly due to my stupid naming mistakes and a misleading changelog. I should have updated all these with a new series patches. But I hope I can polish more in the new patchset with more suggestions from valuable comments, especially in x86,scheduler,percpu and rcu areas.
I'm very obliged to hear anything.
Thanks Lai
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