From: Byungchul Park <byungchul.park@lge.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: peterz@infradead.org, mingo@kernel.org, tglx@linutronix.de,
walken@google.com, kirill@shutemov.name,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, willy@infradead.org,
npiggin@gmail.com, kernel-team@lge.com
Subject: Re: [PATCH v8 06/14] lockdep: Detect and handle hist_lock ring buffer overwrite
Date: Fri, 11 Aug 2017 18:44:48 +0900 [thread overview]
Message-ID: <20170811094448.GJ20323@X58A-UD3R> (raw)
In-Reply-To: <20170811085201.GI20323@X58A-UD3R>
On Fri, Aug 11, 2017 at 05:52:02PM +0900, Byungchul Park wrote:
> On Fri, Aug 11, 2017 at 04:03:29PM +0800, Boqun Feng wrote:
> > Thanks for taking a look at it ;-)
>
> I rather appriciate it.
>
> > > > @@ -5005,7 +5003,7 @@ static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
> > > > static void commit_xhlocks(struct cross_lock *xlock)
> > > > {
> > > > unsigned int cur = current->xhlock_idx;
> > > > - unsigned int prev_hist_id = xhlock(cur).hist_id;
> > > > + unsigned int prev_hist_id = cur + 1;
> > >
> > > I should have named it another. Could you suggest a better one?
> > >
> >
> > I think "prev" is fine, because I thought the "previous" means the
> > xhlock item we visit _previously_.
> >
> > > > unsigned int i;
> > > >
> > > > if (!graph_lock())
> > > > @@ -5030,7 +5028,7 @@ static void commit_xhlocks(struct cross_lock *xlock)
> > > > * hist_id than the following one, which is impossible
> > > > * otherwise.
> > >
> > > Or we need to modify the comment so that the word 'prev' does not make
> > > readers confused. It was my mistake.
> > >
> >
> > I think the comment needs some help, but before you do it, could you
> > have another look at what Peter proposed previously? Note you have a
> > same_context_xhlock() check in the commit_xhlocks(), so the your
> > previous overwrite case actually could be detected, I think.
>
> What is the previous overwrite case?
>
> ppppppppppwwwwwwwwwwwwiiiiiiiii
> iiiiiiiiiiiiiii................
>
> Do you mean this one? I missed the check of same_context_xhlock(). Yes,
> peterz's suggestion also seems to work.
>
> > However, one thing may not be detected is this case:
> >
> > ppppppppppppppppppppppppppppppppppwwwwwwww
> > wrapped > wwwwwww
>
> To be honest, I think your suggestion is more natual, with which this
> case would be also covered.
>
> >
> > where p: process and w: worker.
> >
> > , because p and w are in the same task_irq_context(). I discussed this
> > with Peter yesterday, and he has a good idea: unconditionally do a reset
> > on the ring buffer whenever we do a crossrelease_hist_end(XHLOCK_PROC).
Ah, ok. You meant 'whenever _process_ context exit'.
I need more time to be sure, but anyway for now it seems to work with
giving up some chances for remaining xhlocks.
But, I am not sure if it's still true even in future and the code can be
maintained easily. I think your approach is natural and neat enough for
that purpose. What problem exists with yours?
> > Basically it means we empty the lock history whenever we finished a
> > worker function in a worker thread or we are about to return to
> > userspace after we finish the syscall. This could further save some
> > memory and so I think this may be better than my approach.
>
> Do you mean reset _whenever_ hard irq exit, soft irq exit or work exit?
> Why should we give up chances to check dependencies of remaining xhlocks
> whenever each exit? Am I understanding correctly?
>
> I am just curious. Does your approach have some problems?
>
> Thanks,
> Byungchul
next prev parent reply other threads:[~2017-08-11 9:46 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 7:12 [PATCH v8 00/14] lockdep: Implement crossrelease feature Byungchul Park
2017-08-07 7:12 ` [PATCH v8 01/14] lockdep: Refactor lookup_chain_cache() Byungchul Park
2017-08-10 12:18 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 02/14] lockdep: Add a function building a chain between two classes Byungchul Park
2017-08-10 12:18 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 03/14] lockdep: Change the meaning of check_prev_add()'s return value Byungchul Park
2017-08-10 12:19 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 04/14] lockdep: Make check_prev_add() able to handle external stack_trace Byungchul Park
2017-08-10 12:19 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 05/14] lockdep: Implement crossrelease feature Byungchul Park
2017-08-09 14:05 ` Peter Zijlstra
2017-08-10 1:30 ` Byungchul Park
2017-08-10 9:21 ` Peter Zijlstra
2017-08-10 12:19 ` [tip:locking/core] locking/lockdep: Implement the 'crossrelease' feature tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 06/14] lockdep: Detect and handle hist_lock ring buffer overwrite Byungchul Park
2017-08-09 14:16 ` Peter Zijlstra
2017-08-10 1:32 ` Byungchul Park
2017-08-10 9:22 ` Peter Zijlstra
2017-08-10 10:32 ` Byungchul Park
2017-08-10 11:59 ` Boqun Feng
2017-08-10 12:11 ` Byungchul Park
2017-08-10 12:51 ` Boqun Feng
2017-08-10 13:17 ` Boqun Feng
2017-08-11 0:44 ` Byungchul Park
2017-08-11 3:43 ` Byungchul Park
2017-08-11 8:03 ` Boqun Feng
2017-08-11 8:52 ` Byungchul Park
2017-08-11 9:44 ` Byungchul Park [this message]
2017-08-11 13:06 ` Byungchul Park
2017-08-14 7:05 ` Boqun Feng
2017-08-14 7:22 ` Byungchul Park
2017-08-14 7:29 ` Byungchul Park
2017-08-11 0:40 ` Byungchul Park
2017-08-11 1:03 ` Boqun Feng
2017-08-10 12:20 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 07/14] lockdep: Handle non(or multi)-acquisition of a crosslock Byungchul Park
2017-08-10 12:20 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 08/14] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park
2017-08-10 12:21 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-07 7:12 ` [PATCH v8 09/14] lockdep: Apply crossrelease to completions Byungchul Park
2017-08-07 10:20 ` kbuild test robot
2017-08-07 11:45 ` kbuild test robot
2017-08-09 9:51 ` Peter Zijlstra
2017-08-09 10:24 ` Peter Zijlstra
2017-08-10 1:24 ` Byungchul Park
2017-08-10 12:21 ` [tip:locking/core] locking/lockdep: " tip-bot for Byungchul Park
2017-08-14 8:50 ` [PATCH v8 09/14] lockdep: " Arnd Bergmann
2017-08-18 23:43 ` Boqun Feng
2017-08-19 12:51 ` Arnd Bergmann
2017-08-19 13:34 ` Arnd Bergmann
2017-08-23 14:43 ` Boqun Feng
2017-08-20 3:18 ` Boqun Feng
2017-08-07 7:12 ` [PATCH v8 10/14] pagemap.h: Remove trailing white space Byungchul Park
2017-08-07 7:12 ` [PATCH v8 11/14] lockdep: Apply crossrelease to PG_locked locks Byungchul Park
2017-08-07 10:36 ` kbuild test robot
2017-08-10 1:35 ` Byungchul Park
2017-08-10 9:25 ` Peter Zijlstra
2017-09-05 1:03 ` Byungchul Park
2017-08-07 7:12 ` [PATCH v8 12/14] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2017-08-07 7:13 ` [PATCH v8 13/14] lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2017-08-07 10:43 ` kbuild test robot
2017-08-07 7:13 ` [PATCH v8 14/14] lockdep: Crossrelease feature documentation Byungchul Park
2017-08-07 15:58 ` kbuild test robot
2017-08-10 12:22 ` [tip:locking/core] locking/lockdep: Add 'crossrelease' " tip-bot for Byungchul Park
2017-08-09 15:50 ` [PATCH v8 00/14] lockdep: Implement crossrelease feature Peter Zijlstra
2017-08-10 0:55 ` Byungchul Park
2017-08-10 3:47 ` Byungchul Park
2017-08-10 10:52 ` Byungchul Park
2017-08-10 9:37 ` Byungchul Park
2017-08-10 10:52 ` Peter Zijlstra
2017-08-10 11:10 ` Ingo Molnar
2017-08-10 11:45 ` Byungchul Park
2017-08-14 10:57 ` Ingo Molnar
2017-08-14 11:10 ` Byungchul Park
2017-08-15 8:20 ` Ingo Molnar
2017-08-16 0:16 ` Byungchul Park
2017-08-16 4:05 ` Boqun Feng
2017-08-16 4:37 ` Byungchul Park
2017-08-16 5:40 ` Boqun Feng
2017-08-16 6:37 ` Byungchul Park
2017-08-16 5:05 ` Byungchul Park
2017-08-16 5:58 ` Boqun Feng
2017-08-16 7:14 ` Byungchul Park
2017-08-16 8:06 ` Byungchul Park
2017-08-16 9:38 ` Byungchul Park
2017-08-17 7:48 ` Ingo Molnar
2017-08-17 8:04 ` Boqun Feng
2017-08-17 8:12 ` Ingo Molnar
2017-08-17 8:33 ` Boqun Feng
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