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From: Waiman Long <longman@redhat.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>, Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	linux-mm@kvack.org, Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Tejun Heo <tj@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC PATCH 00/12] locking/lockdep: Add a new class of terminal locks
Date: Mon, 12 Nov 2018 14:56:09 -0800	[thread overview]
Message-ID: <74a54ce2-e71c-d64a-af46-83eb840b96b8@redhat.com> (raw)
In-Reply-To: <20181112222250.h37hkrj6warqewkd@treble>

On 11/12/2018 02:22 PM, Josh Poimboeuf wrote:
> On Mon, Nov 12, 2018 at 07:30:50AM +0100, Ingo Molnar wrote:
>> * Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>>
>>> On Mon, Nov 12, 2018 at 06:10:33AM +0100, Ingo Molnar wrote:
>>>> * Waiman Long <longman@redhat.com> wrote:
>>>>
>>>>> On 11/10/2018 09:10 AM, Peter Zijlstra wrote:
>>>>>> On Fri, Nov 09, 2018 at 09:04:12AM +0100, Ingo Molnar wrote:
>>>>>>> BTW., if you are interested in more radical approaches to optimize 
>>>>>>> lockdep, we could also add a static checker via objtool driven call graph 
>>>>>>> analysis, and mark those locks terminal that we can prove are terminal.
>>>>>>>
>>>>>>> This would require the unified call graph of the kernel image and of all 
>>>>>>> modules to be examined in a final pass, but that's within the principal 
>>>>>>> scope of objtool. (This 'final pass' could also be done during bootup, at 
>>>>>>> least in initial versions.)
>>>>>> Something like this is needed for objtool LTO support as well. I just
>>>>>> dread the build time 'regressions' this will introduce :/
>>>>>>
>>>>>> The final link pass is already by far the most expensive part (as
>>>>>> measured in wall-time) of building a kernel, adding more work there
>>>>>> would really suck :/
>>>>> I think the idea is to make objtool have the capability to do that. It
>>>>> doesn't mean we need to turn it on by default in every build.
>>>> Yeah.
>>>>
>>>> Also note that much of the objtool legwork would be on a per file basis 
>>>> which is reasonably parallelized already. On x86 it's also already done 
>>>> for every ORC build i.e. every distro build and the incremental overhead 
>>>> from also extracting locking dependencies should be reasonably small.
>>>>
>>>> The final search of the global graph would be serialized but still 
>>>> reasonably fast as these are all 'class' level dependencies which are 
>>>> much less numerous than runtime dependencies.
>>>>
>>>> I.e. I think we are talking about tens of thousands of dependencies, not 
>>>> tens of millions.
>>>>
>>>> At least in theory. ;-)
>>> Generating a unified call graph sounds very expensive (and very far
>>> beyond what objtool can do today).
>> Well, objtool already goes through the instruction stream and recognizes 
>> function calls - so it can in effect generate a stream of "function x 
>> called by function y" data, correct?
> Yeah, though it would be quite simple to get the same data with a simple
> awk script at link time.
>
>>>  Also, what about function pointers?
>> So maybe it's possible to enumerate all potential values for function 
>> pointers with a reasonably simple compiler plugin and work from there?
> I think this would be somewhere between very difficult and impossible to
> do properly.  I can't even imagine how this would be implemented in a
> compiler plugin.  But I'd love to be proven wrong on that.

I would say we have to assume for the worst when a function pointer is
being called while holding a lock unless we are able to find out all its
possible targets.

Cheers,
Longman

      reply	other threads:[~2018-11-12 22:56 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-08 20:34 Waiman Long
2018-11-08 20:34 ` [RFC PATCH 01/12] locking/lockdep: Rework lockdep_set_novalidate_class() Waiman Long
2018-11-10 14:14   ` Peter Zijlstra
2018-11-11  0:26     ` Waiman Long
2018-11-11  1:28       ` Peter Zijlstra
2018-11-08 20:34 ` [RFC PATCH 02/12] locking/lockdep: Add a new terminal lock type Waiman Long
2018-11-10 14:17   ` Peter Zijlstra
2018-11-11  0:28     ` Waiman Long
2018-11-08 20:34 ` [RFC PATCH 03/12] locking/lockdep: Add DEFINE_TERMINAL_SPINLOCK() and related macros Waiman Long
2018-11-08 20:34 ` [RFC PATCH 04/12] printk: Make logbuf_lock a terminal lock Waiman Long
2018-11-08 20:34 ` [RFC PATCH 05/12] debugobjects: Mark pool_lock as " Waiman Long
2018-11-08 20:34 ` [RFC PATCH 06/12] debugobjects: Move printk out of db lock critical sections Waiman Long
2018-11-08 20:34 ` [RFC PATCH 07/12] locking/lockdep: Add support for nested terminal locks Waiman Long
2018-11-10 14:20   ` Peter Zijlstra
2018-11-11  0:30     ` Waiman Long
2018-11-11  1:30       ` Peter Zijlstra
2018-11-08 20:34 ` [RFC PATCH 08/12] debugobjects: Make object hash locks " Waiman Long
2018-11-08 20:34 ` [RFC PATCH 09/12] lib/stackdepot: Make depot_lock a terminal spinlock Waiman Long
2018-11-08 20:34 ` [RFC PATCH 10/12] locking/rwsem: Mark rwsem.wait_lock as a terminal lock Waiman Long
2018-11-08 20:34 ` [RFC PATCH 11/12] cgroup: Mark the rstat percpu lock as terminal Waiman Long
2018-11-08 20:34 ` [RFC PATCH 12/12] mm/kasan: Make quarantine_lock a terminal lock Waiman Long
2018-11-09  8:04 ` [RFC PATCH 00/12] locking/lockdep: Add a new class of terminal locks Ingo Molnar
2018-11-09 15:48   ` Waiman Long
2018-11-12  5:15     ` Ingo Molnar
2018-11-10 14:10   ` Peter Zijlstra
2018-11-10 23:35     ` Waiman Long
2018-11-12  5:10       ` Ingo Molnar
2018-11-12  5:53         ` Josh Poimboeuf
2018-11-12  6:30           ` Ingo Molnar
2018-11-12 22:22             ` Josh Poimboeuf
2018-11-12 22:56               ` Waiman Long [this message]

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