From: Boqun Feng <boqun.feng@gmail.com>
To: Byungchul Park <byungchul.park@lge.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 09:03:00 +0800 [thread overview]
Message-ID: <20170811010300.x2vo5yenxzvgujoq@tardis> (raw)
In-Reply-To: <20170811004021.GF20323@X58A-UD3R>
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On Fri, Aug 11, 2017 at 09:40:21AM +0900, Byungchul Park wrote:
> On Thu, Aug 10, 2017 at 08:51:33PM +0800, Boqun Feng wrote:
> > > > > void crossrelease_hist_end(enum context_t c)
> > > > > {
> > > > > - if (current->xhlocks)
> > > > > - current->xhlock_idx = current->xhlock_idx_hist[c];
> > > > > + struct task_struct *cur = current;
> > > > > +
> > > > > + if (cur->xhlocks) {
> > > > > + unsigned int idx = cur->xhlock_idx_hist[c];
> > > > > + struct hist_lock *h = &xhlock(idx);
> > > > > +
> > > > > + cur->xhlock_idx = idx;
> > > > > +
> > > > > + /* Check if the ring was overwritten. */
> > > > > + if (h->hist_id != cur->hist_id_save[c])
> > > >
> > > > Could we use:
> > > >
> > > > if (h->hist_id != idx)
> > >
> > > No, we cannot.
> > >
> >
> > Hey, I'm not buying it. task_struct::hist_id and task_struct::xhlock_idx
> > are increased at the same place(in add_xhlock()), right?
>
> Right.
>
> > And, yes, xhlock_idx will get decreased when we do ring-buffer
>
> This is why we should keep both of them.
>
> > unwinding, but that's OK, because we need to throw away those recently
> > added items.
> >
> > And xhlock_idx always points to the most recently added valid item,
>
> No, it's not true in case that the ring buffer was wrapped like:
>
> ppppppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiii
> wrapped > iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii................
> ^
> xhlock_idx points here after unwinding,
> and it's not a valid one.
>
> where p represents an acquisition in process context,
> i represents an acquisition in irq context.
>
Yeah, but we can detect this with comparison between the
hist_lock::hist_id and the task_struct::xhlock_idx in
commit_xhlocks()(see my patch), no?
Regards,
Boqun
> > right? Any other item's idx must "before()" the most recently added
> > one's, right? So ::xhlock_idx acts just like a timestamp, doesn't it?
>
> Both of two answers are _no_.
>
> > Maybe I'm missing something subtle, but could you show me an example,
> > that could end up being a problem if we use xhlock_idx as the hist_id?
>
> See the example above. We cannot detect whether it was wrapped or not using
> xhlock_idx.
>
> >
> > > hist_id is a kind of timestamp and used to detect overwriting
> > > data into places of same indexes of the ring buffer. And idx is
> > > just an index. :) IOW, they mean different things.
> > >
> > > >
> > > > here, and
> > > >
> > > > > + invalidate_xhlock(h);
> > > > > + }
> > > > > }
> > > > >
> > > > > static int cross_lock(struct lockdep_map *lock)
> > > > > @@ -4826,6 +4851,7 @@ static inline int depend_after(struct held_lock
> > > > *hlock)
> > > > > * Check if the xhlock is valid, which would be false if,
> > > > > *
> > > > > * 1. Has not used after initializaion yet.
> > > > > + * 2. Got invalidated.
> > > > > *
> > > > > * Remind hist_lock is implemented as a ring buffer.
> > > > > */
> > > > > @@ -4857,6 +4883,7 @@ static void add_xhlock(struct held_lock *hlock)
> > > > >
> > > > > /* Initialize hist_lock's members */
> > > > > xhlock->hlock = *hlock;
> > > > > + xhlock->hist_id = current->hist_id++;
> >
> > Besides, is this code correct? Does this just make xhlock->hist_id
> > one-less-than the curr->hist_id, which cause the invalidation every time
> > you do ring buffer unwinding?
>
> Right. "save = hist_id++" should be "save = ++hist_id". Could you fix it?
>
> Thank you,
> Byungchul
>
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next prev parent reply other threads:[~2017-08-11 1:02 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
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 [this message]
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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