[RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Alexey Kardashevskiy]

As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
memory. If there is a bug in memory release, the loop in
tce_iommu_release() becomes infinite; this actually happened to me.

This makes the loop finite and prints a warning on every failure to make
the code more bug prone.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index b1a8ab3..ece0651 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
 {
 	struct tce_container *container = iommu_data;
 	struct tce_iommu_group *tcegrp;
+	struct tce_iommu_prereg *tcemem, *tmtmp;
 	long i;
 
 	while (tce_groups_attached(container)) {
@@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
 		tce_iommu_free_table(container, tbl);
 	}
 
-	while (!list_empty(&container->prereg_list)) {
-		struct tce_iommu_prereg *tcemem;
-
-		tcemem = list_first_entry(&container->prereg_list,
-				struct tce_iommu_prereg, next);
-		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
-	}
+	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
+		WARN_ON(tce_iommu_prereg_free(container, tcemem));
 
 	tce_iommu_disable(container);
 	if (container->mm)
-- 
2.11.0

Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[David Gibson]

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On Tue, Oct 02, 2018 at 01:22:31PM +1000, Alexey Kardashevskiy wrote:
> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

It does improve the current behaviour.  I do suspect, however, that
leaving the failed regions in the list will probably cause another
failure later on.

> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index b1a8ab3..ece0651 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
>  {
>  	struct tce_container *container = iommu_data;
>  	struct tce_iommu_group *tcegrp;
> +	struct tce_iommu_prereg *tcemem, *tmtmp;
>  	long i;
>  
>  	while (tce_groups_attached(container)) {
> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(container, tbl);
>  	}
>  
> -	while (!list_empty(&container->prereg_list)) {
> -		struct tce_iommu_prereg *tcemem;
> -
> -		tcemem = list_first_entry(&container->prereg_list,
> -				struct tce_iommu_prereg, next);
> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
> -	}
> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>  
>  	tce_iommu_disable(container);
>  	if (container->mm)

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Alex Williamson]

On Tue,  2 Oct 2018 13:22:31 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)

Should this have a stable/fixes tag?  Looks like it's relevant to:

4b6fad7097f8 powerpc/mm/iommu, vfio/spapr: Put pages on VFIO container shutdown

Also, not sure who you're wanting to take this since it was sent to ppc
lists.  If it's me, let me know, otherwise

Acked-by: Alex Williamson <alex.williamson@redhat.com>

Thanks,
Alex

> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index b1a8ab3..ece0651 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
>  {
>  	struct tce_container *container = iommu_data;
>  	struct tce_iommu_group *tcegrp;
> +	struct tce_iommu_prereg *tcemem, *tmtmp;
>  	long i;
>  
>  	while (tce_groups_attached(container)) {
> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(container, tbl);
>  	}
>  
> -	while (!list_empty(&container->prereg_list)) {
> -		struct tce_iommu_prereg *tcemem;
> -
> -		tcemem = list_first_entry(&container->prereg_list,
> -				struct tce_iommu_prereg, next);
> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
> -	}
> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>  
>  	tce_iommu_disable(container);
>  	if (container->mm)

Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Serhii Popovych]

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Alexey Kardashevskiy wrote:
> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index b1a8ab3..ece0651 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -371,6 +371,7 @@ static void tce_iommu_release(void *iommu_data)
>  {
>  	struct tce_container *container = iommu_data;
>  	struct tce_iommu_group *tcegrp;
> +	struct tce_iommu_prereg *tcemem, *tmtmp;
>  	long i;
>  
>  	while (tce_groups_attached(container)) {
> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>  		tce_iommu_free_table(container, tbl);
>  	}
>  
> -	while (!list_empty(&container->prereg_list)) {
> -		struct tce_iommu_prereg *tcemem;
> -
> -		tcemem = list_first_entry(&container->prereg_list,
> -				struct tce_iommu_prereg, next);
> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
> -	}
> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));

I'm not sure that tce_iommu_prereg_free() call under WARN_ON() is good
idea because WARN_ON() is a preprocessor macro:

  if CONFIG_WARN=n is added by the analogy with CONFIG_BUG=n defining
  WARN_ON() as empty we will loose call to tce_iommu_prereg_free()
  leaking resources.

There is no problem at the moment: WARN_ON() defined for PPC in
arch/powerpc/include/asm/bug.h unconditionally.

So your first version with intermediate variable looks better to me.

>  
>  	tce_iommu_disable(container);
>  	if (container->mm)
> 


-- 
Thanks,
Serhii


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Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Michael Ellerman]

Serhii Popovych <spopovyc@redhat.com> writes:
> Alexey Kardashevskiy wrote:
>> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
>> memory. If there is a bug in memory release, the loop in
>> tce_iommu_release() becomes infinite; this actually happened to me.
>> 
>> This makes the loop finite and prints a warning on every failure to make
>> the code more bug prone.
>> 
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>>  1 file changed, 3 insertions(+), 7 deletions(-)
>> 
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index b1a8ab3..ece0651 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>>  		tce_iommu_free_table(container, tbl);
>>  	}
>>  
>> -	while (!list_empty(&container->prereg_list)) {
>> -		struct tce_iommu_prereg *tcemem;
>> -
>> -		tcemem = list_first_entry(&container->prereg_list,
>> -				struct tce_iommu_prereg, next);
>> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
>> -	}
>> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
>> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>
> I'm not sure that tce_iommu_prereg_free() call under WARN_ON() is good
> idea because WARN_ON() is a preprocessor macro:
>
>   if CONFIG_WARN=n is added by the analogy with CONFIG_BUG=n defining
>   WARN_ON() as empty we will loose call to tce_iommu_prereg_free()
>   leaking resources.

I don't think that's likely to ever happen though, we have a large
number of uses that would need to be checked one-by-one:

  $ git grep "if (WARN_ON(" | wc -l
  2853


So if we ever did add CONFIG_WARN, I think it would still need to
evaluate the condition, just not emit a warning.

cheers

Re: [RFC PATCH kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Alexey Kardashevskiy]

On 08/10/2018 21:18, Michael Ellerman wrote:
> Serhii Popovych <spopovyc@redhat.com> writes:
>> Alexey Kardashevskiy wrote:
>>> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
>>> memory. If there is a bug in memory release, the loop in
>>> tce_iommu_release() becomes infinite; this actually happened to me.
>>>
>>> This makes the loop finite and prints a warning on every failure to make
>>> the code more bug prone.
>>>
>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>> ---
>>>  drivers/vfio/vfio_iommu_spapr_tce.c | 10 +++-------
>>>  1 file changed, 3 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>>> index b1a8ab3..ece0651 100644
>>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>>> @@ -393,13 +394,8 @@ static void tce_iommu_release(void *iommu_data)
>>>  		tce_iommu_free_table(container, tbl);
>>>  	}
>>>  
>>> -	while (!list_empty(&container->prereg_list)) {
>>> -		struct tce_iommu_prereg *tcemem;
>>> -
>>> -		tcemem = list_first_entry(&container->prereg_list,
>>> -				struct tce_iommu_prereg, next);
>>> -		WARN_ON_ONCE(tce_iommu_prereg_free(container, tcemem));
>>> -	}
>>> +	list_for_each_entry_safe(tcemem, tmtmp, &container->prereg_list, next)
>>> +		WARN_ON(tce_iommu_prereg_free(container, tcemem));
>>
>> I'm not sure that tce_iommu_prereg_free() call under WARN_ON() is good
>> idea because WARN_ON() is a preprocessor macro:
>>
>>   if CONFIG_WARN=n is added by the analogy with CONFIG_BUG=n defining
>>   WARN_ON() as empty we will loose call to tce_iommu_prereg_free()
>>   leaking resources.
> 
> I don't think that's likely to ever happen though, we have a large
> number of uses that would need to be checked one-by-one:
> 
>   $ git grep "if (WARN_ON(" | wc -l
>   2853
> 
> 
> So if we ever did add CONFIG_WARN, I think it would still need to
> evaluate the condition, just not emit a warning.

Is anyone taking this?


-- 
Alexey

Re: [RFC,kernel] vfio/spapr_tce: Get rid of possible infinite loop

[Michael Ellerman]

On Tue, 2018-10-02 at 03:22:31 UTC, Alexey Kardashevskiy wrote:
> As a part of cleanup, the SPAPR TCE IOMMU subdriver releases preregistered
> memory. If there is a bug in memory release, the loop in
> tce_iommu_release() becomes infinite; this actually happened to me.
> 
> This makes the loop finite and prints a warning on every failure to make
> the code more bug prone.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> Acked-by: Alex Williamson <alex.williamson@redhat.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/517ad4ae8aa93dccdb9a88c27257ec

cheers