Am 10/7/2024 um 3:18 PM schrieb David Laight:
From: Jonas Oberhauser
Sent: 07 October 2024 12:55
Am 10/3/2024 um 3:23 PM schrieb Mathieu Desnoyers:
What _does_ work however are the following two approaches:
1) Perform the equality check on the original variables, creating
new versions (wit
On 2024-10-07 15:18, David Laight wrote:
From: Jonas Oberhauser
Sent: 07 October 2024 12:55
Am 10/3/2024 um 3:23 PM schrieb Mathieu Desnoyers:
What _does_ work however are the following two approaches:
1) Perform the equality check on the original variables, creating
new versions (with OPTIMI
From: Jonas Oberhauser
> Sent: 07 October 2024 12:55
>
> Am 10/3/2024 um 3:23 PM schrieb Mathieu Desnoyers:
> > What _does_ work however are the following two approaches:
> >
> > 1) Perform the equality check on the original variables, creating
> > new versions (with OPTIMIZER_HIDE_VAR) of both va
Am 10/3/2024 um 3:23 PM schrieb Mathieu Desnoyers:
What _does_ work however are the following two approaches:
1) Perform the equality check on the original variables, creating
new versions (with OPTIMIZER_HIDE_VAR) of both variables for the
rest of their use, therefore making sure the pointer
On 2024-10-03 19:07, David Laight wrote:
...
What _does_ work however are the following two approaches:
1) Perform the equality check on the original variables, creating
new versions (with OPTIMIZER_HIDE_VAR) of both variables for the
rest of their use, therefore making sure the pointer derefer
...
> What _does_ work however are the following two approaches:
>
> 1) Perform the equality check on the original variables, creating
> new versions (with OPTIMIZER_HIDE_VAR) of both variables for the
> rest of their use, therefore making sure the pointer dereference
> are not derived from versio
On 2024-10-03 03:50, 'Alan Stern' wrote:
On Wed, Oct 02, 2024 at 03:24:45PM +, David Laight wrote:
I think I know what you are trying to do, and you just fail.
Whether something can work is another matter, but that code
can't ever work.
Inside if (a == b) the compiler will always use the sa
On Wed, Oct 02, 2024 at 03:24:45PM +, David Laight wrote:
> I think I know what you are trying to do, and you just fail.
> Whether something can work is another matter, but that code
> can't ever work.
>
> Inside if (a == b) the compiler will always use the same register
> for references to a
From: 'Alan Stern'
> Sent: 02 October 2024 15:15
>
> On Wed, Oct 02, 2024 at 08:13:15AM +, David Laight wrote:
> > From: 'Alan Stern'
> > > Sent: 01 October 2024 23:57
> > >
> > > On Tue, Oct 01, 2024 at 05:11:05PM +, David Laight wrote:
> > > > From: Alan Stern
> > > > > Sent: 30 Septembe
On Wed, Oct 02, 2024 at 08:13:15AM +, David Laight wrote:
> From: 'Alan Stern'
> > Sent: 01 October 2024 23:57
> >
> > On Tue, Oct 01, 2024 at 05:11:05PM +, David Laight wrote:
> > > From: Alan Stern
> > > > Sent: 30 September 2024 19:53
> > > >
> > > > On Mon, Sep 30, 2024 at 07:05:06PM +
From: 'Alan Stern'
> Sent: 01 October 2024 23:57
>
> On Tue, Oct 01, 2024 at 05:11:05PM +, David Laight wrote:
> > From: Alan Stern
> > > Sent: 30 September 2024 19:53
> > >
> > > On Mon, Sep 30, 2024 at 07:05:06PM +0200, Jonas Oberhauser wrote:
> > > >
> > > >
> > > > Am 9/30/2024 um 6:43 PM
On Tue, Oct 01, 2024 at 05:11:05PM +, David Laight wrote:
> From: Alan Stern
> > Sent: 30 September 2024 19:53
> >
> > On Mon, Sep 30, 2024 at 07:05:06PM +0200, Jonas Oberhauser wrote:
> > >
> > >
> > > Am 9/30/2024 um 6:43 PM schrieb Alan Stern:
> > > > On Mon, Sep 30, 2024 at 01:26:53PM +020
From: Alan Stern
> Sent: 30 September 2024 19:53
>
> On Mon, Sep 30, 2024 at 07:05:06PM +0200, Jonas Oberhauser wrote:
> >
> >
> > Am 9/30/2024 um 6:43 PM schrieb Alan Stern:
> > > On Mon, Sep 30, 2024 at 01:26:53PM +0200, Jonas Oberhauser wrote:
> > > >
> > > >
> > > > Am 9/28/2024 um 4:49 PM sch
On Mon, Sep 30, 2024 at 07:05:06PM +0200, Jonas Oberhauser wrote:
>
>
> Am 9/30/2024 um 6:43 PM schrieb Alan Stern:
> > On Mon, Sep 30, 2024 at 01:26:53PM +0200, Jonas Oberhauser wrote:
> > >
> > >
> > > Am 9/28/2024 um 4:49 PM schrieb Alan Stern:
> > >
> > > I should also point out that it is
Am 9/30/2024 um 6:43 PM schrieb Alan Stern:
On Mon, Sep 30, 2024 at 01:26:53PM +0200, Jonas Oberhauser wrote:
Am 9/28/2024 um 4:49 PM schrieb Alan Stern:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
Compiler CSE and SSA GVN optimizations can cause the address depende
On Mon, Sep 30, 2024 at 01:26:53PM +0200, Jonas Oberhauser wrote:
>
>
> Am 9/28/2024 um 4:49 PM schrieb Alan Stern:
> > On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
> > > Compiler CSE and SSA GVN optimizations can cause the address dependency
> > > of addresses returned by r
On Mon, Sep 30, 2024 at 02:06:12PM +0200, Jonas Oberhauser wrote:
>
>
> Am 9/30/2024 um 1:04 PM schrieb Paul E. McKenney:
> > On Mon, Sep 30, 2024 at 11:42:11AM +0200, Jonas Oberhauser wrote:
> > >
> > >
> > > I also currently don't see any major difference between the constant and
> > > regist
Am 9/30/2024 um 1:04 PM schrieb Paul E. McKenney:
On Mon, Sep 30, 2024 at 11:42:11AM +0200, Jonas Oberhauser wrote:
I also currently don't see any major difference between the constant and
register case. The point is that the address is known before loading into b,
and hence the compiler +
Am 9/28/2024 um 4:49 PM schrieb Alan Stern:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
Compiler CSE and SSA GVN optimizations can cause the address dependency
of addresses returned by rcu_dereference to be lost when comparing those
pointers with either constants or pre
On Mon, Sep 30, 2024 at 11:42:11AM +0200, Jonas Oberhauser wrote:
>
>
> Am 9/28/2024 um 11:15 PM schrieb Alan Stern:
> > On Sat, Sep 28, 2024 at 11:55:22AM -0400, Mathieu Desnoyers wrote:
> > > On 2024-09-28 17:49, Alan Stern wrote:
> > > > Isn't it true that on strongly ordered CPUs, a compiler
On Sep 30, 2024, at 17:33, Jonas Oberhauser
wrote:
>
>
>
> Am 9/30/2024 um 11:27 AM schrieb Alan Huang:
>> 2024年9月30日 17:15，Alan Huang 写道：
>>>
>>> 2024年9月30日 16:57，Jonas Oberhauser 写道：
Am 9/29/2024 um 12:26 AM schrieb Alan Huang:
> 2024年9月28日 23:55，Mathieu Desnoye
Am 9/28/2024 um 11:15 PM schrieb Alan Stern:
On Sat, Sep 28, 2024 at 11:55:22AM -0400, Mathieu Desnoyers wrote:
On 2024-09-28 17:49, Alan Stern wrote:
Isn't it true that on strongly ordered CPUs, a compiler barrier is
sufficient to prevent the rcu_dereference() problem? So the whole idea
be
Am 9/30/2024 um 11:27 AM schrieb Alan Huang:
2024年9月30日 17:15，Alan Huang 写道：
2024年9月30日 16:57，Jonas Oberhauser 写道：
Am 9/29/2024 um 12:26 AM schrieb Alan Huang:
2024年9月28日 23:55，Mathieu Desnoyers wrote：
The motivation for introducing ptr_eq() is indeed because the
compiler barrier i
2024年9月30日 17:15，Alan Huang 写道：
>
> 2024年9月30日 16:57，Jonas Oberhauser 写道：
>>
>>
>>
>> Am 9/29/2024 um 12:26 AM schrieb Alan Huang:
>>> 2024年9月28日 23:55，Mathieu Desnoyers wrote：
On 2024-09-28 17:49, Alan Stern wrote:
> On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers
2024年9月30日 16:57，Jonas Oberhauser 写道：
>
>
>
> Am 9/29/2024 um 12:26 AM schrieb Alan Huang:
>> 2024年9月28日 23:55，Mathieu Desnoyers wrote：
>>>
>>> On 2024-09-28 17:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
> On 2024-09-28 16:49, Alan Stern
Am 9/29/2024 um 12:26 AM schrieb Alan Huang:
2024年9月28日 23:55，Mathieu Desnoyers wrote：
On 2024-09-28 17:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
On 2024-09-28 16:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoy
On 2024-09-29 01:24, Gary Guo wrote:
Cc: Nikita Popov
Cc: l...@lists.linux.dev
On Sat, 28 Sep 2024 09:51:27 -0400
Mathieu Desnoyers wrote:
Compiler CSE and SSA GVN optimizations can cause the address dependency
of addresses returned by rcu_dereference to be lost when comparing those
pointers
2024年9月29日 07:55，Boqun Feng wrote：
>
>
>
> On Sun, Sep 29, 2024, at 6:26 AM, Alan Huang wrote:
>> 2024年9月28日 23:55，Mathieu Desnoyers wrote：
>>>
>>> On 2024-09-28 17:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
> On 2024-09-28 16:49, Alan St
On Sun, Sep 29, 2024, at 6:26 AM, Alan Huang wrote:
> 2024年9月28日 23:55，Mathieu Desnoyers wrote：
>>
>> On 2024-09-28 17:49, Alan Stern wrote:
>>> On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
On 2024-09-28 16:49, Alan Stern wrote:
> On Sat, Sep 28, 2024 at 09:51:27
Cc: Nikita Popov
Cc: l...@lists.linux.dev
On Sat, 28 Sep 2024 09:51:27 -0400
Mathieu Desnoyers wrote:
> Compiler CSE and SSA GVN optimizations can cause the address dependency
> of addresses returned by rcu_dereference to be lost when comparing those
> pointers with either constants or previous
2024年9月28日 23:55，Mathieu Desnoyers wrote：
>
> On 2024-09-28 17:49, Alan Stern wrote:
>> On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
>>> On 2024-09-28 16:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
> equality, which does
On Sat, Sep 28, 2024 at 11:55:22AM -0400, Mathieu Desnoyers wrote:
> On 2024-09-28 17:49, Alan Stern wrote:
> > On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
> > > On 2024-09-28 16:49, Alan Stern wrote:
> > > > On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
On 2024-09-28 17:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
On 2024-09-28 16:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
equality, which does not preserve address dependencies and allows the
following mi
On Sat, Sep 28, 2024 at 11:32:18AM -0400, Mathieu Desnoyers wrote:
> On 2024-09-28 16:49, Alan Stern wrote:
> > On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
> > > equality, which does not preserve address dependencies and allows the
> > > following misordering speculations:
>
On 2024-09-28 16:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
Compiler CSE and SSA GVN optimizations can cause the address dependency
of addresses returned by rcu_dereference to be lost when comparing those
pointers with either constants or previously
On 2024-09-28 16:49, Alan Stern wrote:
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
[...]
+/*
+ * Compare two addresses while preserving the address dependencies for
+ * later use of the address. It should be used when comparing an address
+ * returned by rcu_dereference()
On Sat, Sep 28, 2024 at 09:51:27AM -0400, Mathieu Desnoyers wrote:
> Compiler CSE and SSA GVN optimizations can cause the address dependency
> of addresses returned by rcu_dereference to be lost when comparing those
> pointers with either constants or previously loaded pointers.
>
> Introduce ptr_
Compiler CSE and SSA GVN optimizations can cause the address dependency
of addresses returned by rcu_dereference to be lost when comparing those
pointers with either constants or previously loaded pointers.
Introduce ptr_eq() to compare two addresses while preserving the address
dependencies for l
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