From: Michel Lespinasse <walken@google.com>
To: Michel Lespinasse <walken@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.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>,
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 v2 07/10] mmap locking API: add mmap_read_release() and mmap_read_unlock_non_owner()
Date: Thu, 26 Mar 2020 22:09:09 -0700 [thread overview]
Message-ID: <CANN689Hr972e_0+kujGxXPbCVTd7xnpBPZXDk2T3dwARnWENVQ@mail.gmail.com> (raw)
In-Reply-To: <20200327044647.wgfsmjy37n72dixe@linux-p48b>
On Thu, Mar 26, 2020 at 9:48 PM Davidlohr Bueso <dave@stgolabs.net> wrote:
>
> On Thu, 26 Mar 2020, Michel Lespinasse wrote:
>
> >Add a couple APIs to allow splitting mmap_read_unlock() into two calls:
> >- mmap_read_release(), called by the task that had taken the mmap lock;
> >- mmap_read_unlock_non_owner(), called from a work queue.
> >
> >These apis are used by kernel/bpf/stackmap.c only.
>
> I'm not crazy about the idea generalizing such calls into an mm api.
> We try to stay away from non-owner semantics in locking - granted
> the IS_ENABLED(CONFIG_PREEMPT_RT) warning, but still.
>
> Could this give future users the wrong impression? What about just
> using rwsem calls directly in bpf?
I see what you mean and I certainly don't want to encourage any new
non-owner call sites to appear.... This bpf stackmap site is a small
pain point in my larger range locking patchset too.
I am not sure what is the proper response to it; the opposite side of
your argument could be that using a direct rwsem call there hides the
issue and makes it less likely for someone to fix it ? I don't have a
very strong opinion on this, as I think it can be argued either way...
But at a minimum, I think it'd be worth adding a comment asking people
not to add new call sites to the mmap_read_release() and
mmap_read_unlock_non_owner() APIs ?
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
next prev parent reply other threads:[~2020-03-27 5:09 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 2:10 [PATCH v2 00/10] Add a new mmap locking API wrapping mmap_sem calls Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 01/10] mmap locking API: initial implementation as rwsem wrappers Michel Lespinasse
2020-03-27 12:16 ` Jason Gunthorpe
2020-03-27 21:52 ` Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 02/10] MMU notifier: use the new mmap locking API Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 03/10] DMA reservations: " Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 04/10] mmap locking API: use coccinelle to convert mmap_sem rwsem call sites Michel Lespinasse
2020-03-27 7:22 ` Markus Elfring
2020-03-27 7:44 ` Michel Lespinasse
2020-03-27 8:00 ` [v2 " Markus Elfring
2020-03-27 8:08 ` Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 05/10] mmap locking API: convert mmap_sem call sites missed by coccinelle Michel Lespinasse
2020-03-27 8:21 ` Markus Elfring
2020-03-27 2:10 ` [PATCH v2 06/10] mmap locking API: convert nested write lock sites Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 07/10] mmap locking API: add mmap_read_release() and mmap_read_unlock_non_owner() Michel Lespinasse
2020-03-27 4:46 ` Davidlohr Bueso
2020-03-27 5:09 ` Michel Lespinasse [this message]
2020-03-27 2:10 ` [PATCH v2 08/10] mmap locking API: add MMAP_LOCK_INITIALIZER Michel Lespinasse
2020-03-27 2:10 ` [PATCH v2 09/10] mmap locking API: use lockdep_assert_held Michel Lespinasse
2020-03-27 4:48 ` Davidlohr Bueso
2020-03-27 2:10 ` [PATCH v2 10/10] mmap locking API: rename mmap_sem to mmap_lock Michel Lespinasse
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