From: Jann Horn <jannh@google.com>
To: David Howells <dhowells@redhat.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
raven@themaw.net, linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
linux-block@vger.kernel.org, keyrings@vger.kernel.org,
linux-security-module <linux-security-module@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer
Date: Wed, 29 May 2019 19:46:54 +0200 [thread overview]
Message-ID: <CAG48ez0R-R3Xs+3Xg9T9qcV3Xv6r4pnx1Z2y=Ltx7RGOayte_w@mail.gmail.com> (raw)
In-Reply-To: <31936.1559146000@warthog.procyon.org.uk>
On Wed, May 29, 2019 at 6:07 PM David Howells <dhowells@redhat.com> wrote:
> Greg KH <gregkh@linuxfoundation.org> wrote:
> > everyone should use
> > it. It saves us having to audit the same pattern over and over again.
> > And, even nicer, it uses a refcount now, and as you are trying to
> > reference count an object, it is exactly what this was written for.
> >
> > So yes, I do think it should be used here, unless it is deemed to not
> > fit the pattern/usage model.
>
> kref_put() enforces a very specific destructor signature. I know of places
> where that doesn't work because the destructor takes more than one argument
> (granted that this is not the case here). So why does kref_put() exist at
> all? Why not kref_dec_and_test()?
>
> Why doesn't refcount_t get merged into kref, or vice versa? Having both would
> seem redundant.
>
> Mind you, I've been gradually reverting atomic_t-to-refcount_t conversions
> because it seems I'm not allowed refcount_inc/dec_return() and I want to get
> at the point refcount for tracing purposes.
Yeeech, that's horrible, please don't do that.
Does this mean that refcount_read() isn't sufficient for what you want
to do with tracing (because for some reason you actually need to know
the values atomically at the time of increment/decrement)?
WARNING: multiple messages have this Message-ID (diff)
From: Jann Horn <jannh@google.com>
To: David Howells <dhowells@redhat.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
raven@themaw.net, linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
linux-block@vger.kernel.org, keyrings@vger.kernel.org,
linux-security-module <linux-security-module@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer
Date: Wed, 29 May 2019 17:46:54 +0000 [thread overview]
Message-ID: <CAG48ez0R-R3Xs+3Xg9T9qcV3Xv6r4pnx1Z2y=Ltx7RGOayte_w@mail.gmail.com> (raw)
In-Reply-To: <31936.1559146000@warthog.procyon.org.uk>
On Wed, May 29, 2019 at 6:07 PM David Howells <dhowells@redhat.com> wrote:
> Greg KH <gregkh@linuxfoundation.org> wrote:
> > everyone should use
> > it. It saves us having to audit the same pattern over and over again.
> > And, even nicer, it uses a refcount now, and as you are trying to
> > reference count an object, it is exactly what this was written for.
> >
> > So yes, I do think it should be used here, unless it is deemed to not
> > fit the pattern/usage model.
>
> kref_put() enforces a very specific destructor signature. I know of places
> where that doesn't work because the destructor takes more than one argument
> (granted that this is not the case here). So why does kref_put() exist at
> all? Why not kref_dec_and_test()?
>
> Why doesn't refcount_t get merged into kref, or vice versa? Having both would
> seem redundant.
>
> Mind you, I've been gradually reverting atomic_t-to-refcount_t conversions
> because it seems I'm not allowed refcount_inc/dec_return() and I want to get
> at the point refcount for tracing purposes.
Yeeech, that's horrible, please don't do that.
Does this mean that refcount_read() isn't sufficient for what you want
to do with tracing (because for some reason you actually need to know
the values atomically at the time of increment/decrement)?
next prev parent reply other threads:[~2019-05-29 17:47 UTC|newest]
Thread overview: 131+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 16:01 [RFC][PATCH 0/7] Mount, FS, Block and Keyrings notifications David Howells
2019-05-28 16:01 ` David Howells
2019-05-28 16:01 ` [PATCH 1/7] General notification queue with user mmap()'able ring buffer David Howells
2019-05-28 16:01 ` David Howells
2019-05-28 16:26 ` Greg KH
2019-05-28 16:26 ` Greg KH
2019-05-28 17:30 ` David Howells
2019-05-28 17:30 ` David Howells
2019-05-28 23:12 ` Greg KH
2019-05-28 23:12 ` Greg KH
2019-05-29 16:06 ` David Howells
2019-05-29 16:06 ` David Howells
2019-05-29 17:46 ` Jann Horn [this message]
2019-05-29 17:46 ` Jann Horn
2019-05-29 21:02 ` David Howells
2019-05-29 21:02 ` David Howells
2019-05-31 11:14 ` Peter Zijlstra
2019-05-31 11:14 ` Peter Zijlstra
2019-05-31 12:02 ` David Howells
2019-05-31 12:02 ` David Howells
2019-05-31 13:26 ` Peter Zijlstra
2019-05-31 13:26 ` Peter Zijlstra
2019-05-31 14:20 ` David Howells
2019-05-31 14:20 ` David Howells
2019-05-31 16:44 ` Peter Zijlstra
2019-05-31 16:44 ` Peter Zijlstra
2019-05-31 17:12 ` David Howells
2019-05-31 17:12 ` David Howells
2019-06-17 16:24 ` Peter Zijlstra
2019-06-17 16:24 ` Peter Zijlstra
2019-05-29 23:09 ` Greg KH
2019-05-29 23:09 ` Greg KH
2019-05-29 23:11 ` Greg KH
2019-05-29 23:11 ` Greg KH
2019-05-30 9:50 ` Andrea Parri
2019-05-30 9:50 ` Andrea Parri
2019-05-31 8:35 ` Peter Zijlstra
2019-05-31 8:35 ` Peter Zijlstra
2019-05-31 8:47 ` Peter Zijlstra
2019-05-31 8:47 ` Peter Zijlstra
2019-05-31 12:42 ` David Howells
2019-05-31 12:42 ` David Howells
2019-05-31 14:55 ` David Howells
2019-05-31 14:55 ` David Howells
2019-05-28 19:14 ` Jann Horn
2019-05-28 19:14 ` Jann Horn
2019-05-28 22:28 ` David Howells
2019-05-28 22:28 ` David Howells
2019-05-28 23:16 ` Jann Horn
2019-05-28 23:16 ` Jann Horn
2019-05-28 16:02 ` [PATCH 2/7] keys: Add a notification facility David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 16:02 ` [PATCH 3/7] vfs: Add a mount-notification facility David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:06 ` Jann Horn
2019-05-28 20:06 ` Jann Horn
2019-05-28 23:04 ` David Howells
2019-05-28 23:04 ` David Howells
2019-05-28 23:23 ` Jann Horn
2019-05-28 23:23 ` Jann Horn
2019-05-29 11:16 ` David Howells
2019-05-29 11:16 ` David Howells
2019-05-28 23:08 ` David Howells
2019-05-28 23:08 ` David Howells
2019-05-29 10:55 ` David Howells
2019-05-29 10:55 ` David Howells
2019-05-29 11:00 ` David Howells
2019-05-29 11:00 ` David Howells
2019-05-29 15:53 ` Casey Schaufler
2019-05-29 15:53 ` Casey Schaufler
2019-05-29 16:12 ` Jann Horn
2019-05-29 16:12 ` Jann Horn
2019-05-29 17:04 ` Casey Schaufler
2019-05-29 17:04 ` Casey Schaufler
2019-06-03 16:30 ` David Howells
2019-06-03 16:30 ` David Howells
2019-05-29 17:13 ` Andy Lutomirski
2019-05-29 17:13 ` Andy Lutomirski
2019-05-29 17:46 ` Casey Schaufler
2019-05-29 17:46 ` Casey Schaufler
2019-05-29 18:11 ` Jann Horn
2019-05-29 18:11 ` Jann Horn
2019-05-29 19:28 ` Casey Schaufler
2019-05-29 19:28 ` Casey Schaufler
2019-05-29 19:47 ` Jann Horn
2019-05-29 19:47 ` Jann Horn
2019-05-29 20:50 ` Casey Schaufler
2019-05-29 20:50 ` Casey Schaufler
2019-05-29 23:12 ` Andy Lutomirski
2019-05-29 23:12 ` Andy Lutomirski
2019-05-29 23:56 ` Casey Schaufler
2019-05-29 23:56 ` Casey Schaufler
2019-05-28 16:02 ` [PATCH 4/7] vfs: Add superblock notifications David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:27 ` Jann Horn
2019-05-28 20:27 ` Jann Horn
2019-05-29 12:58 ` David Howells
2019-05-29 12:58 ` David Howells
2019-05-29 14:16 ` Jann Horn
2019-05-29 14:16 ` Jann Horn
2019-05-28 16:02 ` [PATCH 5/7] fsinfo: Export superblock notification counter David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 16:02 ` [PATCH 6/7] block: Add block layer notifications David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 20:37 ` Jann Horn
2019-05-28 20:37 ` Jann Horn
2019-05-28 16:02 ` [PATCH 7/7] Add sample notification program David Howells
2019-05-28 16:02 ` David Howells
2019-05-28 23:58 ` [RFC][PATCH 0/7] Mount, FS, Block and Keyrings notifications Greg KH
2019-05-28 23:58 ` Greg KH
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 6:33 ` Amir Goldstein
2019-05-29 14:25 ` Jan Kara
2019-05-29 14:25 ` Jan Kara
2019-05-29 15:10 ` Greg KH
2019-05-29 15:10 ` Greg KH
2019-05-29 15:53 ` Amir Goldstein
2019-05-29 15:53 ` Amir Goldstein
2019-05-30 11:00 ` Jan Kara
2019-05-30 11:00 ` Jan Kara
2019-06-04 12:33 ` David Howells
2019-06-04 12:33 ` David Howells
2019-05-29 6:45 ` David Howells
2019-05-29 6:45 ` David Howells
2019-05-29 7:40 ` Amir Goldstein
2019-05-29 7:40 ` Amir Goldstein
2019-05-29 9:09 ` David Howells
2019-05-29 9:09 ` David Howells
2019-05-29 15:41 ` Casey Schaufler
2019-05-29 15:41 ` Casey Schaufler
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