From: Peter Zijlstra <peterz@infradead.org>
To: Michel Lespinasse <walken@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Laurent Dufour <ldufour@linux.ibm.com>,
Vlastimil Babka <vbabka@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
Liam Howlett <Liam.Howlett@oracle.com>,
Jerome Glisse <jglisse@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
David Rientjes <rientjes@google.com>,
Hugh Dickins <hughd@google.com>, Ying Han <yinghan@google.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Markus Elfring <Markus.Elfring@web.de>
Subject: Re: [PATCH v3 06/10] mmap locking API: convert nested write lock sites
Date: Mon, 6 Apr 2020 17:58:34 +0200 [thread overview]
Message-ID: <20200406155834.GR20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CANN689H1VjW4aC8HuLEtb8YrVyAJ0t6OVM6w2_o1+P2=9Mt6Gw@mail.gmail.com>
On Mon, Apr 06, 2020 at 08:35:03AM -0700, Michel Lespinasse wrote:
> On Wed, Apr 1, 2020 at 6:42 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Mar 27, 2020 at 03:50:58PM -0700, Michel Lespinasse wrote:
> >
> > > @@ -26,6 +31,12 @@ static inline void mmap_write_unlock(struct mm_struct *mm)
> > > up_write(&mm->mmap_sem);
> > > }
> > >
> > > +/* Pairs with mmap_write_lock_nested() */
> > > +static inline void mmap_write_unlock_nested(struct mm_struct *mm)
> > > +{
> > > + up_write(&mm->mmap_sem);
> > > +}
> > > +
> > > static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
> > > {
> > > downgrade_write(&mm->mmap_sem);
> >
> > Why does unlock_nested() make sense ?
>
> I thought it would make things more explicit to match the nested lock
> with the corresponding unlock site; however this information is not
> used at the moment (i.e. the nested unlock is implemented identically
> to the regular unlock).
>
> Having the matching sites explicitly identified may help when
> implementing lock instrumentation, or when changing the lock type
> (another patchset I am working on needs to pass an explicit lock range
> to the nested lock and unlock sites).
>
> I'll admit this is not a super strong argument, and can be deferred to
> when an actual need shows up in the future.
The thing is, lock-acquisition order matters _a_lot_, lock-release order
is irrelevant. ISTR there was a thread about this some 14 years ago, but
please don't ask me to go find it :/
next prev parent reply other threads:[~2020-04-06 15:58 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 22:50 [PATCH v3 00/10] Add a new mmap locking API wrapping mmap_sem calls Michel Lespinasse
2020-03-27 22:50 ` [PATCH v3 01/10] mmap locking API: initial implementation as rwsem wrappers Michel Lespinasse
2020-03-28 8:57 ` [PATCH v3 01/10] mmap locking API: initial implementation as rwsem wrappers (Michel Lespinasse) SeongJae Park
2020-03-27 22:50 ` [PATCH v3 02/10] MMU notifier: use the new mmap locking API Michel Lespinasse
2020-03-27 22:50 ` [PATCH v3 03/10] DMA reservations: " Michel Lespinasse
2020-03-27 22:50 ` [PATCH v3 04/10] mmap locking API: use coccinelle to convert mmap_sem rwsem call sites Michel Lespinasse
2020-03-27 22:50 ` [PATCH v3 05/10] mmap locking API: convert mmap_sem call sites missed by coccinelle Michel Lespinasse
2020-03-28 7:36 ` Markus Elfring
2020-03-28 7:47 ` Michel Lespinasse
2020-03-28 8:39 ` [v3 " Markus Elfring
2020-03-28 8:53 ` Michel Lespinasse
2020-03-28 9:01 ` Markus Elfring
2020-03-28 13:20 ` [v3 05/10] mmap locking API: Checking the Coccinelle software Markus Elfring
2020-03-28 13:42 ` [Cocci] " Julia Lawall
2020-03-28 13:52 ` Markus Elfring
2020-03-28 13:53 ` Julia Lawall
2020-03-28 14:00 ` Julia Lawall
2020-03-28 14:16 ` Markus Elfring
2020-03-30 6:10 ` [v3 05/10] mmap locking API: Improving " Markus Elfring
2020-03-30 8:47 ` [Cocci] " Julia Lawall
2020-03-30 10:15 ` Markus Elfring
2020-03-30 10:20 ` Julia Lawall
2020-03-30 10:42 ` Markus Elfring
2020-04-13 17:06 ` [PATCH v3 05/10] mmap locking API: convert mmap_sem call sites missed by coccinelle Daniel Jordan
2020-03-27 22:50 ` [PATCH v3 06/10] mmap locking API: convert nested write lock sites Michel Lespinasse
2020-04-01 13:42 ` Peter Zijlstra
2020-04-06 15:35 ` Michel Lespinasse
2020-04-06 15:58 ` Peter Zijlstra [this message]
2020-03-27 22:50 ` [PATCH v3 07/10] mmap locking API: add mmap_read_release() and mmap_read_unlock_non_owner() Michel Lespinasse
2020-04-01 13:46 ` Peter Zijlstra
2020-04-06 15:39 ` Michel Lespinasse
2020-03-27 22:51 ` [PATCH v3 08/10] mmap locking API: add MMAP_LOCK_INITIALIZER Michel Lespinasse
2020-03-27 22:51 ` [PATCH v3 09/10] mmap locking API: use lockdep_assert_held Michel Lespinasse
2020-03-27 22:51 ` [PATCH v3 10/10] mmap locking API: rename mmap_sem to mmap_lock Michel Lespinasse
2020-04-01 13:48 ` Peter Zijlstra
2020-04-06 15:49 ` Michel Lespinasse
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