From: Boqun Feng <boqun.feng@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, tglx@linutronix.de, walken@google.com,
kirill@shutemov.name, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, iamjoonsoo.kim@lge.com,
akpm@linux-foundation.org, npiggin@gmail.com
Subject: Re: [PATCH v4 07/15] lockdep: Implement crossrelease feature
Date: Tue, 17 Jan 2017 14:24:08 +0800 [thread overview]
Message-ID: <20170117062408.GE15084@tardis.cn.ibm.com> (raw)
In-Reply-To: <20170117023341.GG3326@X58A-UD3R>
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On Tue, Jan 17, 2017 at 11:33:41AM +0900, Byungchul Park wrote:
> On Mon, Jan 16, 2017 at 04:13:19PM +0100, Peter Zijlstra wrote:
> > On Fri, Dec 09, 2016 at 02:12:03PM +0900, Byungchul Park wrote:
> > > + /*
> > > + * We assign class_idx here redundantly even though following
> > > + * memcpy will cover it, in order to ensure a rcu reader can
> > > + * access the class_idx atomically without lock.
> > > + *
> > > + * Here we assume setting a word-sized variable is atomic.
> >
> > which one, where?
>
> I meant xlock_class(xlock) in check_add_plock().
>
> I was not sure about the following two.
>
> 1. Is it ordered between following a and b?
> a. memcpy -> list_add_tail_rcu
> b. list_for_each_entry_rcu -> load class_idx (xlock_class)
> I assumed that it's not ordered.
> 2. Does memcpy guarantee atomic store for each word?
> I assumed that it doesn't.
>
> But I think I was wrong.. The first might be ordered. I will remove
> the following redundant statement. It'd be orderd, right?
>
Yes, a and b are ordered, IOW, they could be paired, meaning when we
got the item in a list_for_each_entry_rcu() loop, all memory operations
before the corresponding list_add_tail_rcu() should be observed by us.
Regards,
Boqun
> >
> > > + */
> > > + xlock->hlock.class_idx = hlock->class_idx;
> > > + gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
> > > + WRITE_ONCE(xlock->gen_id, gen_id);
> > > + memcpy(&xlock->hlock, hlock, sizeof(struct held_lock));
> > > + INIT_LIST_HEAD(&xlock->xlock_entry);
> > > + list_add_tail_rcu(&xlock->xlock_entry, &xlocks_head);
> >
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next prev parent reply other threads:[~2017-01-17 6:23 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-09 5:11 [PATCH v4 00/15] " Byungchul Park
2016-12-09 5:11 ` [PATCH v4 01/15] x86/dumpstack: Optimize save_stack_trace Byungchul Park
2016-12-09 5:11 ` [PATCH v4 02/15] x86/dumpstack: Add save_stack_trace()_fast() Byungchul Park
2016-12-09 5:11 ` [PATCH v4 03/15] lockdep: Refactor lookup_chain_cache() Byungchul Park
2016-12-09 5:12 ` [PATCH v4 04/15] lockdep: Add a function building a chain between two classes Byungchul Park
2017-01-10 21:00 ` Peter Zijlstra
2017-01-12 1:41 ` Byungchul Park
2016-12-09 5:12 ` [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate stack_trace Byungchul Park
2017-01-12 16:16 ` Peter Zijlstra
2017-01-13 2:45 ` Byungchul Park
2017-01-13 10:11 ` Byungchul Park
2017-01-17 15:54 ` Peter Zijlstra
2017-01-18 2:04 ` Byungchul Park
2017-01-18 15:10 ` Peter Zijlstra
2017-01-19 2:47 ` Byungchul Park
2016-12-09 5:12 ` [PATCH v4 06/15] lockdep: Make save_trace can skip stack tracing of the current Byungchul Park
2017-01-12 16:37 ` Peter Zijlstra
2017-01-13 0:18 ` Byungchul Park
2016-12-09 5:12 ` [PATCH v4 07/15] lockdep: Implement crossrelease feature Byungchul Park
2017-01-13 4:39 ` Lai Jiangshan
2017-01-13 5:02 ` Byungchul Park
2017-01-16 15:10 ` Peter Zijlstra
2017-01-17 2:05 ` Byungchul Park
2017-01-17 7:12 ` Peter Zijlstra
2017-01-17 7:49 ` Byungchul Park
2017-01-17 7:14 ` Peter Zijlstra
2017-01-17 7:45 ` Byungchul Park
2017-01-16 15:13 ` Peter Zijlstra
2017-01-17 2:33 ` Byungchul Park
2017-01-17 6:24 ` Boqun Feng [this message]
2017-01-17 7:43 ` Byungchul Park
2016-12-09 5:12 ` [PATCH v4 08/15] lockdep: Make crossrelease use save_stack_trace_fast() Byungchul Park
2016-12-09 5:12 ` [PATCH v4 09/15] lockdep: Make print_circular_bug() crosslock-aware Byungchul Park
2016-12-09 5:12 ` [PATCH v4 10/15] lockdep: Apply crossrelease to completion operation Byungchul Park
2016-12-09 5:12 ` [PATCH v4 11/15] pagemap.h: Remove trailing white space Byungchul Park
2016-12-09 5:12 ` [PATCH v4 12/15] lockdep: Apply crossrelease to PG_locked lock Byungchul Park
2016-12-09 5:12 ` [PATCH v4 13/15] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2016-12-09 5:12 ` [PATCH v4 14/15] lockdep: Move data used in CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2016-12-09 5:12 ` [PATCH v4 15/15] lockdep: Crossrelease feature documentation Byungchul Park
2017-01-10 20:08 ` Peter Zijlstra
2017-01-11 1:29 ` Byungchul Park
2017-01-18 6:42 ` Boqun Feng
2017-01-18 10:53 ` Byungchul Park
2017-01-18 11:03 ` Peter Zijlstra
2017-01-18 11:54 ` Byungchul Park
2017-01-18 12:07 ` Peter Zijlstra
2017-01-18 12:14 ` byungchul.park
2017-01-18 14:12 ` Peter Zijlstra
2017-01-19 1:54 ` Byungchul Park
2017-01-18 12:49 ` byungchul.park
2016-12-09 5:21 ` [FYI] Output of 'cat /proc/lockdep' after applying crossrelease Byungchul Park
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