[PATCH v2] eal: fix thread race in control thread creation

[PATCH v2] eal: fix thread race in control thread creation

[Tyler Retzlaff]

When ctrl_thread_init transitions params->ctrl_thread_status from
CTRL_THREAD_LAUNCHING the creating thread and new thread may run
concurrently leading to unsynchronized access to params.

This permits races for both the failure and success paths after
ctrl_thread_status is stored.
  * params->ret may be loaded in ctrl_thread_init failure path
  * params->arg may be loaded in ctrl_thread_start or
    control_thread_start when calling start_routine.

For ctrl_thread_init remove the params->ret load and just return 1 since
it is only interpreted as a indicator of success / failure of
ctrl_thread_init.

For {ctrl,control}_thread_start store param->arg in stack allocated
storage prior to calling ctrl_thread_init and use the copy when calling
start_routine.

For control_thread_start if ctrl_thread_init fails just return 0 instead
of loading params->ret, since the value returned is unused when
ctrl_thread_status is set to CTRL_THREAD_ERROR when ctrl_thread_init
fails.

Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")

Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
---
 lib/eal/common/eal_common_thread.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
index edb9d4e..079a385 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
 	if (params->ret != 0) {
 		__atomic_store_n(&params->ctrl_thread_status,
 			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
-		return params->ret;
+		return 1;
 	}
 
 	__atomic_store_n(&params->ctrl_thread_status,
@@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)
 static void *ctrl_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
 		return NULL;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 static uint32_t control_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	rte_thread_func start_routine = params->u.control_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
-		return params->ret;
+		return 0;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 int
-- 
1.8.3.1

Re: [PATCH v2] eal: fix thread race in control thread creation

[David Marchand]

On Wed, Mar 1, 2023 at 10:09 PM Tyler Retzlaff
<roretzla@linux.microsoft.com> wrote:
>
> When ctrl_thread_init transitions params->ctrl_thread_status from
> CTRL_THREAD_LAUNCHING the creating thread and new thread may run
> concurrently leading to unsynchronized access to params.
>
> This permits races for both the failure and success paths after
> ctrl_thread_status is stored.
>   * params->ret may be loaded in ctrl_thread_init failure path
>   * params->arg may be loaded in ctrl_thread_start or
>     control_thread_start when calling start_routine.
>
> For ctrl_thread_init remove the params->ret load and just return 1 since
> it is only interpreted as a indicator of success / failure of
> ctrl_thread_init.
>
> For {ctrl,control}_thread_start store param->arg in stack allocated
> storage prior to calling ctrl_thread_init and use the copy when calling
> start_routine.
>
> For control_thread_start if ctrl_thread_init fails just return 0 instead
> of loading params->ret, since the value returned is unused when
> ctrl_thread_status is set to CTRL_THREAD_ERROR when ctrl_thread_init
> fails.
>
> Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")
>
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> Reviewed-by: David Marchand <david.marchand@redhat.com>

Honnappa reached out offlist and proposed to send the discussed rework
as a followup patch.
So I'll take this fix as is for now.

Applied, thanks Tyler.


-- 
David Marchand

Re: [PATCH v2] eal: fix thread race in control thread creation

[Tyler Retzlaff]

On Tue, Mar 07, 2023 at 02:53:34PM +0100, David Marchand wrote:
> On Thu, Mar 2, 2023 at 5:18 AM Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com> wrote:
> > > > >   if (ctrl_thread_init(arg) != 0)
> > > > >           return NULL;
> > > > >
> > > > > - return start_routine(params->arg);
> > > > > + return start_routine(start_arg);
> > > > We can free 'params' here after 'start_routine' returns.
> > >
> > > I guess it doesn't matter if the allocation is retained for the duration of
> > > start_routine() which could be ~long.
> > Yes, that's what I thought, it is a small size.
> >
> > >
> > > David/Honnappah let me know what you decide. if you'd prefer to change to
> > > honnappah's suggestion i'll put a new version up.
> 
> Hum, how would it look like?
> - the parent thread would free params if the child thread fails to set affinity,
> - the child thread would free params otherwise,
> 
> Is this what you propose?
> 
> This works, but we have to be extra careful if any change is done in
> this part later.

i think the fix i've already put up is kind of trivially verifiable as
correct, if we just need a fix then it works.

> 
> 
> -- 
> David Marchand

Re: [PATCH v2] eal: fix thread race in control thread creation

[David Marchand]

On Thu, Mar 2, 2023 at 5:18 AM Honnappa Nagarahalli
<Honnappa.Nagarahalli@arm.com> wrote:
> > > >   if (ctrl_thread_init(arg) != 0)
> > > >           return NULL;
> > > >
> > > > - return start_routine(params->arg);
> > > > + return start_routine(start_arg);
> > > We can free 'params' here after 'start_routine' returns.
> >
> > I guess it doesn't matter if the allocation is retained for the duration of
> > start_routine() which could be ~long.
> Yes, that's what I thought, it is a small size.
>
> >
> > David/Honnappah let me know what you decide. if you'd prefer to change to
> > honnappah's suggestion i'll put a new version up.

Hum, how would it look like?
- the parent thread would free params if the child thread fails to set affinity,
- the child thread would free params otherwise,

Is this what you propose?

This works, but we have to be extra careful if any change is done in
this part later.


-- 
David Marchand

RE: [PATCH v2] eal: fix thread race in control thread creation

[Honnappa Nagarahalli]

<snip>

> > >
> > > When ctrl_thread_init transitions params->ctrl_thread_status from
> > > CTRL_THREAD_LAUNCHING the creating thread and new thread may run
> > > concurrently leading to unsynchronized access to params.
> > IMO, the code will be simpler if we did not free 'params' in
> 'rte_thread_create_control'/'rte_ctrl_thread_create'. We could avoid creating
> the local copies of start_routine and the arg.
> 
> You mean in the success case i assume? it still has to be free'd if
> rte_thread_create fails.
Yes

> 
> > See more comments below.
> >
> > >
> > > This permits races for both the failure and success paths after
> > > ctrl_thread_status is stored.
> > >   * params->ret may be loaded in ctrl_thread_init failure path
> > >   * params->arg may be loaded in ctrl_thread_start or
> > >     control_thread_start when calling start_routine.
> > >
> > > For ctrl_thread_init remove the params->ret load and just return 1
> > > since it is only interpreted as a indicator of success / failure of
> ctrl_thread_init.
> > >
> > > For {ctrl,control}_thread_start store param->arg in stack allocated
> > > storage prior to calling ctrl_thread_init and use the copy when calling
> start_routine.
> > >
> > > For control_thread_start if ctrl_thread_init fails just return 0
> > > instead of loading
> > > params->ret, since the value returned is unused when
> > > params->ctrl_thread_status is set
> > > to CTRL_THREAD_ERROR when ctrl_thread_init fails.
> > >
> > > Fixes: 878b7468eacb ("eal: add platform agnostic control thread
> > > API")
> > >
> > > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > Reviewed-by: David Marchand <david.marchand@redhat.com>
> > > ---
> > >  lib/eal/common/eal_common_thread.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/lib/eal/common/eal_common_thread.c
> > > b/lib/eal/common/eal_common_thread.c
> > > index edb9d4e..079a385 100644
> > > --- a/lib/eal/common/eal_common_thread.c
> > > +++ b/lib/eal/common/eal_common_thread.c
> > > @@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
> > >  	if (params->ret != 0) {
> > >  		__atomic_store_n(&params->ctrl_thread_status,
> > >  			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
> > > -		return params->ret;
> > > +		return 1;
> > >  	}
> > >
> > >  	__atomic_store_n(&params->ctrl_thread_status,
> > > @@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)  static
> > > void *ctrl_thread_start(void *arg)  {
> > >  	struct rte_thread_ctrl_params *params = arg;
> > > +	void *start_arg = params->arg;
> > >  	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
> > These copies can be avoided, code will be much simpler
> >
> > >
> > >  	if (ctrl_thread_init(arg) != 0)
> > >  		return NULL;
> > >
> > > -	return start_routine(params->arg);
> > > +	return start_routine(start_arg);
> > We can free 'params' here after 'start_routine' returns.
> 
> I guess it doesn't matter if the allocation is retained for the duration of
> start_routine() which could be ~long.
Yes, that's what I thought, it is a small size.

> 
> David/Honnappah let me know what you decide. if you'd prefer to change to
> honnappah's suggestion i'll put a new version up.
> 
> >
> > >  }
> > >
> > >  static uint32_t control_thread_start(void *arg)  {
> > >  	struct rte_thread_ctrl_params *params = arg;
> > > +	void *start_arg = params->arg;
> > >  	rte_thread_func start_routine = params->u.control_start_routine;
> > >
> > >  	if (ctrl_thread_init(arg) != 0)
> > > -		return params->ret;
> > > +		return 0;
> > >
> > > -	return start_routine(params->arg);
> > > +	return start_routine(start_arg);
> > >  }
> > >
> > >  int
> > > --
> > > 1.8.3.1

Re: [PATCH v2] eal: fix thread race in control thread creation

[Tyler Retzlaff]

On Thu, Mar 02, 2023 at 01:30:13AM +0000, Honnappa Nagarahalli wrote:
> 
> 
> > -----Original Message-----
> > From: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Sent: Wednesday, March 1, 2023 3:10 PM
> > To: dev@dpdk.org; david.marchand@redhat.com
> > Cc: thomas@monjalon.net; Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Subject: [PATCH v2] eal: fix thread race in control thread creation
> > 
> > When ctrl_thread_init transitions params->ctrl_thread_status from
> > CTRL_THREAD_LAUNCHING the creating thread and new thread may run
> > concurrently leading to unsynchronized access to params.
> IMO, the code will be simpler if we did not free 'params' in 'rte_thread_create_control'/'rte_ctrl_thread_create'. We could avoid creating the local copies of start_routine and the arg.

You mean in the success case i assume? it still has to be free'd if
rte_thread_create fails.

> See more comments below.
> 
> > 
> > This permits races for both the failure and success paths after ctrl_thread_status
> > is stored.
> >   * params->ret may be loaded in ctrl_thread_init failure path
> >   * params->arg may be loaded in ctrl_thread_start or
> >     control_thread_start when calling start_routine.
> > 
> > For ctrl_thread_init remove the params->ret load and just return 1 since it is
> > only interpreted as a indicator of success / failure of ctrl_thread_init.
> > 
> > For {ctrl,control}_thread_start store param->arg in stack allocated storage prior
> > to calling ctrl_thread_init and use the copy when calling start_routine.
> > 
> > For control_thread_start if ctrl_thread_init fails just return 0 instead of loading
> > params->ret, since the value returned is unused when ctrl_thread_status is set
> > to CTRL_THREAD_ERROR when ctrl_thread_init fails.
> > 
> > Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")
> > 
> > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Reviewed-by: David Marchand <david.marchand@redhat.com>
> > ---
> >  lib/eal/common/eal_common_thread.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/eal/common/eal_common_thread.c
> > b/lib/eal/common/eal_common_thread.c
> > index edb9d4e..079a385 100644
> > --- a/lib/eal/common/eal_common_thread.c
> > +++ b/lib/eal/common/eal_common_thread.c
> > @@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
> >  	if (params->ret != 0) {
> >  		__atomic_store_n(&params->ctrl_thread_status,
> >  			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
> > -		return params->ret;
> > +		return 1;
> >  	}
> > 
> >  	__atomic_store_n(&params->ctrl_thread_status,
> > @@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)  static void
> > *ctrl_thread_start(void *arg)  {
> >  	struct rte_thread_ctrl_params *params = arg;
> > +	void *start_arg = params->arg;
> >  	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
> These copies can be avoided, code will be much simpler
> 
> > 
> >  	if (ctrl_thread_init(arg) != 0)
> >  		return NULL;
> > 
> > -	return start_routine(params->arg);
> > +	return start_routine(start_arg);
> We can free 'params' here after 'start_routine' returns.

I guess it doesn't matter if the allocation is retained for the duration
of start_routine() which could be ~long.

David/Honnappah let me know what you decide. if you'd prefer to change
to honnappah's suggestion i'll put a new version up.

> 
> >  }
> > 
> >  static uint32_t control_thread_start(void *arg)  {
> >  	struct rte_thread_ctrl_params *params = arg;
> > +	void *start_arg = params->arg;
> >  	rte_thread_func start_routine = params->u.control_start_routine;
> > 
> >  	if (ctrl_thread_init(arg) != 0)
> > -		return params->ret;
> > +		return 0;
> > 
> > -	return start_routine(params->arg);
> > +	return start_routine(start_arg);
> >  }
> > 
> >  int
> > --
> > 1.8.3.1

RE: [PATCH v2] eal: fix thread race in control thread creation

[Honnappa Nagarahalli]

> -----Original Message-----
> From: Tyler Retzlaff <roretzla@linux.microsoft.com>
> Sent: Wednesday, March 1, 2023 3:10 PM
> To: dev@dpdk.org; david.marchand@redhat.com
> Cc: thomas@monjalon.net; Tyler Retzlaff <roretzla@linux.microsoft.com>
> Subject: [PATCH v2] eal: fix thread race in control thread creation
> 
> When ctrl_thread_init transitions params->ctrl_thread_status from
> CTRL_THREAD_LAUNCHING the creating thread and new thread may run
> concurrently leading to unsynchronized access to params.
IMO, the code will be simpler if we did not free 'params' in 'rte_thread_create_control'/'rte_ctrl_thread_create'. We could avoid creating the local copies of start_routine and the arg.
See more comments below.

> 
> This permits races for both the failure and success paths after ctrl_thread_status
> is stored.
>   * params->ret may be loaded in ctrl_thread_init failure path
>   * params->arg may be loaded in ctrl_thread_start or
>     control_thread_start when calling start_routine.
> 
> For ctrl_thread_init remove the params->ret load and just return 1 since it is
> only interpreted as a indicator of success / failure of ctrl_thread_init.
> 
> For {ctrl,control}_thread_start store param->arg in stack allocated storage prior
> to calling ctrl_thread_init and use the copy when calling start_routine.
> 
> For control_thread_start if ctrl_thread_init fails just return 0 instead of loading
> params->ret, since the value returned is unused when ctrl_thread_status is set
> to CTRL_THREAD_ERROR when ctrl_thread_init fails.
> 
> Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")
> 
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> Reviewed-by: David Marchand <david.marchand@redhat.com>
> ---
>  lib/eal/common/eal_common_thread.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/eal/common/eal_common_thread.c
> b/lib/eal/common/eal_common_thread.c
> index edb9d4e..079a385 100644
> --- a/lib/eal/common/eal_common_thread.c
> +++ b/lib/eal/common/eal_common_thread.c
> @@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
>  	if (params->ret != 0) {
>  		__atomic_store_n(&params->ctrl_thread_status,
>  			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
> -		return params->ret;
> +		return 1;
>  	}
> 
>  	__atomic_store_n(&params->ctrl_thread_status,
> @@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)  static void
> *ctrl_thread_start(void *arg)  {
>  	struct rte_thread_ctrl_params *params = arg;
> +	void *start_arg = params->arg;
>  	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
These copies can be avoided, code will be much simpler

> 
>  	if (ctrl_thread_init(arg) != 0)
>  		return NULL;
> 
> -	return start_routine(params->arg);
> +	return start_routine(start_arg);
We can free 'params' here after 'start_routine' returns.

>  }
> 
>  static uint32_t control_thread_start(void *arg)  {
>  	struct rte_thread_ctrl_params *params = arg;
> +	void *start_arg = params->arg;
>  	rte_thread_func start_routine = params->u.control_start_routine;
> 
>  	if (ctrl_thread_init(arg) != 0)
> -		return params->ret;
> +		return 0;
> 
> -	return start_routine(params->arg);
> +	return start_routine(start_arg);
>  }
> 
>  int
> --
> 1.8.3.1

[PATCH v2] eal: fix thread race in control thread creation

[Tyler Retzlaff]

When ctrl_thread_init transitions params->ctrl_thread_status from
CTRL_THREAD_LAUNCHING the creating thread and new thread may run
concurrently leading to unsynchronized access to params.

This permits races for both the failure and success paths after
ctrl_thread_status is stored.
  * params->ret may be loaded in ctrl_thread_init failure path
  * params->arg may be loaded in ctrl_thread_start or
    control_thread_start when calling start_routine.

For ctrl_thread_init remove the params->ret load and just return 1 since
it is only interpreted as a indicator of success / failure of
ctrl_thread_init.

For {ctrl,control}_thread_start store param->arg in stack allocated
storage prior to calling ctrl_thread_init and use the copy when calling
start_routine.

For control_thread_start if ctrl_thread_init fails just return 0 instead
of loading params->ret, since the value returned is unused when
ctrl_thread_status is set to CTRL_THREAD_ERROR when ctrl_thread_init
fails.

Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")

Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
---
 lib/eal/common/eal_common_thread.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
index edb9d4e..079a385 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
 	if (params->ret != 0) {
 		__atomic_store_n(&params->ctrl_thread_status,
 			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
-		return params->ret;
+		return 1;
 	}
 
 	__atomic_store_n(&params->ctrl_thread_status,
@@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)
 static void *ctrl_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
 		return NULL;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 static uint32_t control_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	rte_thread_func start_routine = params->u.control_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
-		return params->ret;
+		return 0;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 int
-- 
1.8.3.1