[PATCH] md: raid10: remove VLAIS

[PATCH] md: raid10: remove VLAIS

[Matthias Kaehlcke]

The raid10 driver can't be built with clang since it uses a variable
length array in a structure (VLAIS):

drivers/md/raid10.c:4583:17: error: fields must have a constant size:
  'variable length array in structure' extension will never be supported

Allocate the r10bio struct with kmalloc instead of using the VLAIS
construct.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 drivers/md/raid10.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 374df5796649..9616163eaf8c 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
 	/* Use sync reads to get the blocks from somewhere else */
 	int sectors = r10_bio->sectors;
 	struct r10conf *conf = mddev->private;
-	struct {
-		struct r10bio r10_bio;
-		struct r10dev devs[conf->copies];
-	} on_stack;
-	struct r10bio *r10b = &on_stack.r10_bio;
+	struct r10bio *r10b;
 	int slot = 0;
 	int idx = 0;
 	struct page **pages;
 
+	r10b = kmalloc(sizeof(*r10b) +
+	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
+	if (!r10b)
+		return -ENOMEM;
+
 	/* reshape IOs share pages from .devs[0].bio */
 	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
 
@@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
 			/* couldn't read this block, must give up */
 			set_bit(MD_RECOVERY_INTR,
 				&mddev->recovery);
+			kfree(r10b);
 			return -EIO;
 		}
 		sectors -= s;
 		idx++;
 	}
+	kfree(r10b);
 	return 0;
 }
 
-- 
2.14.2.920.gcf0c67979c-goog

Re: [PATCH] md: raid10: remove VLAIS

[Guenter Roeck]

On Thu, Oct 5, 2017 at 11:28 AM, Matthias Kaehlcke <mka@chromium.org> wrote:
> The raid10 driver can't be built with clang since it uses a variable
> length array in a structure (VLAIS):
>
> drivers/md/raid10.c:4583:17: error: fields must have a constant size:
>   'variable length array in structure' extension will never be supported
>
> Allocate the r10bio struct with kmalloc instead of using the VLAIS
> construct.
>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Reviewed-by: Guenter Roeck <groeck@chromium.org>

> ---
>  drivers/md/raid10.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 374df5796649..9616163eaf8c 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
>         /* Use sync reads to get the blocks from somewhere else */
>         int sectors = r10_bio->sectors;
>         struct r10conf *conf = mddev->private;
> -       struct {
> -               struct r10bio r10_bio;
> -               struct r10dev devs[conf->copies];
> -       } on_stack;
> -       struct r10bio *r10b = &on_stack.r10_bio;
> +       struct r10bio *r10b;
>         int slot = 0;
>         int idx = 0;
>         struct page **pages;
>
> +       r10b = kmalloc(sizeof(*r10b) +
> +              sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
> +       if (!r10b)
> +               return -ENOMEM;
> +
>         /* reshape IOs share pages from .devs[0].bio */
>         pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
>
> @@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
>                         /* couldn't read this block, must give up */
>                         set_bit(MD_RECOVERY_INTR,
>                                 &mddev->recovery);
> +                       kfree(r10b);
>                         return -EIO;
>                 }
>                 sectors -= s;
>                 idx++;
>         }
> +       kfree(r10b);
>         return 0;
>  }
>
> --
> 2.14.2.920.gcf0c67979c-goog
>

Re: [PATCH] md: raid10: remove VLAIS

[Shaohua Li]

On Thu, Oct 05, 2017 at 11:28:47AM -0700, Matthias Kaehlcke wrote:
> The raid10 driver can't be built with clang since it uses a variable
> length array in a structure (VLAIS):
> 
> drivers/md/raid10.c:4583:17: error: fields must have a constant size:
>   'variable length array in structure' extension will never be supported
> 
> Allocate the r10bio struct with kmalloc instead of using the VLAIS
> construct.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  drivers/md/raid10.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 374df5796649..9616163eaf8c 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
>  	/* Use sync reads to get the blocks from somewhere else */
>  	int sectors = r10_bio->sectors;
>  	struct r10conf *conf = mddev->private;
> -	struct {
> -		struct r10bio r10_bio;
> -		struct r10dev devs[conf->copies];
> -	} on_stack;
> -	struct r10bio *r10b = &on_stack.r10_bio;
> +	struct r10bio *r10b;
>  	int slot = 0;
>  	int idx = 0;
>  	struct page **pages;
>  
> +	r10b = kmalloc(sizeof(*r10b) +
> +	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
> +	if (!r10b)
> +		return -ENOMEM;

I'll apply this patch with 'set_bit(MD_RECOVERY_INTR, &mddev->recovery);' added here, thanks!

> +
>  	/* reshape IOs share pages from .devs[0].bio */
>  	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
>  
> @@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
>  			/* couldn't read this block, must give up */
>  			set_bit(MD_RECOVERY_INTR,
>  				&mddev->recovery);
> +			kfree(r10b);
>  			return -EIO;
>  		}
>  		sectors -= s;
>  		idx++;
>  	}
> +	kfree(r10b);
>  	return 0;
>  }
>  
> -- 
> 2.14.2.920.gcf0c67979c-goog
> 

Re: [PATCH] md: raid10: remove VLAIS

[NeilBrown]

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On Thu, Oct 05 2017, Matthias Kaehlcke wrote:

> The raid10 driver can't be built with clang since it uses a variable
> length array in a structure (VLAIS):
>
> drivers/md/raid10.c:4583:17: error: fields must have a constant size:
>   'variable length array in structure' extension will never be supported
>
> Allocate the r10bio struct with kmalloc instead of using the VLAIS
> construct.
>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  drivers/md/raid10.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 374df5796649..9616163eaf8c 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
>  	/* Use sync reads to get the blocks from somewhere else */
>  	int sectors = r10_bio->sectors;
>  	struct r10conf *conf = mddev->private;
> -	struct {
> -		struct r10bio r10_bio;
> -		struct r10dev devs[conf->copies];
> -	} on_stack;
> -	struct r10bio *r10b = &on_stack.r10_bio;
> +	struct r10bio *r10b;
>  	int slot = 0;
>  	int idx = 0;
>  	struct page **pages;
>  
> +	r10b = kmalloc(sizeof(*r10b) +
> +	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);

GFP_KERNEL isn't a good idea here.
This could wait for writeback, and if writeback tries to write to the
region of the array which is being reshaped, it might deadlock.

GFP_NOIO is safer.

given that conf->copies is almost always 2 it might be nicer to
have

	struct {
		struct r10bio r10_bio;
		struct r10dev devs[2];
	} on_stack;

        struct r10bio *r10b;

	if (conf->copies <= ARRAY_SIZE(on_stack.devs))
        	r10b = &on_stack.r10_bio;
        else
        	r10b = kmalloc(sizeof(*r10b) +
			       sizeof(struct r10dev) * conf->copies, GFP_NOIO);


Thanks,
NeilBrown


> +	if (!r10b)
> +		return -ENOMEM;
> +
>  	/* reshape IOs share pages from .devs[0].bio */
>  	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
>  
> @@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
>  			/* couldn't read this block, must give up */
>  			set_bit(MD_RECOVERY_INTR,
>  				&mddev->recovery);
> +			kfree(r10b);
>  			return -EIO;
>  		}
>  		sectors -= s;
>  		idx++;
>  	}
> +	kfree(r10b);
>  	return 0;
>  }
>  
> -- 
> 2.14.2.920.gcf0c67979c-goog

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Re: [PATCH] md: raid10: remove VLAIS

[Matthias Kaehlcke]

Hi Neil,

El Fri, Oct 06, 2017 at 10:58:59AM +1100 NeilBrown ha dit:

> On Thu, Oct 05 2017, Matthias Kaehlcke wrote:
> 
> > The raid10 driver can't be built with clang since it uses a variable
> > length array in a structure (VLAIS):
> >
> > drivers/md/raid10.c:4583:17: error: fields must have a constant size:
> >   'variable length array in structure' extension will never be supported
> >
> > Allocate the r10bio struct with kmalloc instead of using the VLAIS
> > construct.
> >
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> >  drivers/md/raid10.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index 374df5796649..9616163eaf8c 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
> >  	/* Use sync reads to get the blocks from somewhere else */
> >  	int sectors = r10_bio->sectors;
> >  	struct r10conf *conf = mddev->private;
> > -	struct {
> > -		struct r10bio r10_bio;
> > -		struct r10dev devs[conf->copies];
> > -	} on_stack;
> > -	struct r10bio *r10b = &on_stack.r10_bio;
> > +	struct r10bio *r10b;
> >  	int slot = 0;
> >  	int idx = 0;
> >  	struct page **pages;
> >  
> > +	r10b = kmalloc(sizeof(*r10b) +
> > +	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
> 
> GFP_KERNEL isn't a good idea here.
> This could wait for writeback, and if writeback tries to write to the
> region of the array which is being reshaped, it might deadlock.
> 
> GFP_NOIO is safer.

Good point, thanks!

> given that conf->copies is almost always 2 it might be nicer to
> have
> 
> 	struct {
> 		struct r10bio r10_bio;
> 		struct r10dev devs[2];
> 	} on_stack;
> 
>         struct r10bio *r10b;
> 
> 	if (conf->copies <= ARRAY_SIZE(on_stack.devs))
>         	r10b = &on_stack.r10_bio;
>         else
>         	r10b = kmalloc(sizeof(*r10b) +
> 			       sizeof(struct r10dev) * conf->copies, GFP_NOIO);

It would add also add an extra condition to determine if r10b needs to
be freed or not.

Given that array reshaping is a rare operation and an error during
this operation is an exceptional condition I think the simpler code
with always dynamic allocation is preferable. That said I'm fine with
reworking the patch according to your suggestion if you or Shaohua
prefer it.

Matthias

> > +	if (!r10b)
> > +		return -ENOMEM;
> > +
> >  	/* reshape IOs share pages from .devs[0].bio */
> >  	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
> >  
> > @@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
> >  			/* couldn't read this block, must give up */
> >  			set_bit(MD_RECOVERY_INTR,
> >  				&mddev->recovery);
> > +			kfree(r10b);
> >  			return -EIO;
> >  		}
> >  		sectors -= s;
> >  		idx++;
> >  	}
> > +	kfree(r10b);
> >  	return 0;
> >  }
> >  

Re: [PATCH] md: raid10: remove VLAIS

[NeilBrown]

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On Thu, Oct 05 2017, Matthias Kaehlcke wrote:

> Hi Neil,
>
> El Fri, Oct 06, 2017 at 10:58:59AM +1100 NeilBrown ha dit:
>
>> On Thu, Oct 05 2017, Matthias Kaehlcke wrote:
>> 
>> > The raid10 driver can't be built with clang since it uses a variable
>> > length array in a structure (VLAIS):
>> >
>> > drivers/md/raid10.c:4583:17: error: fields must have a constant size:
>> >   'variable length array in structure' extension will never be supported
>> >
>> > Allocate the r10bio struct with kmalloc instead of using the VLAIS
>> > construct.
>> >
>> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
>> > ---
>> >  drivers/md/raid10.c | 13 ++++++++-----
>> >  1 file changed, 8 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>> > index 374df5796649..9616163eaf8c 100644
>> > --- a/drivers/md/raid10.c
>> > +++ b/drivers/md/raid10.c
>> > @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
>> >  	/* Use sync reads to get the blocks from somewhere else */
>> >  	int sectors = r10_bio->sectors;
>> >  	struct r10conf *conf = mddev->private;
>> > -	struct {
>> > -		struct r10bio r10_bio;
>> > -		struct r10dev devs[conf->copies];
>> > -	} on_stack;
>> > -	struct r10bio *r10b = &on_stack.r10_bio;
>> > +	struct r10bio *r10b;
>> >  	int slot = 0;
>> >  	int idx = 0;
>> >  	struct page **pages;
>> >  
>> > +	r10b = kmalloc(sizeof(*r10b) +
>> > +	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
>> 
>> GFP_KERNEL isn't a good idea here.
>> This could wait for writeback, and if writeback tries to write to the
>> region of the array which is being reshaped, it might deadlock.
>> 
>> GFP_NOIO is safer.
>
> Good point, thanks!
>
>> given that conf->copies is almost always 2 it might be nicer to
>> have
>> 
>> 	struct {
>> 		struct r10bio r10_bio;
>> 		struct r10dev devs[2];
>> 	} on_stack;
>> 
>>         struct r10bio *r10b;
>> 
>> 	if (conf->copies <= ARRAY_SIZE(on_stack.devs))
>>         	r10b = &on_stack.r10_bio;
>>         else
>>         	r10b = kmalloc(sizeof(*r10b) +
>> 			       sizeof(struct r10dev) * conf->copies, GFP_NOIO);
>
> It would add also add an extra condition to determine if r10b needs to
> be freed or not.

True.

>
> Given that array reshaping is a rare operation and an error during
> this operation is an exceptional condition I think the simpler code
> with always dynamic allocation is preferable. That said I'm fine with
> reworking the patch according to your suggestion if you or Shaohua
> prefer it.

I don't feel strongly about it.  As long as the GFP_KERNEL->GFP_NOIO
change happens I'm OK with this patch.

Thanks,
NeilBrown

>
> Matthias
>
>> > +	if (!r10b)
>> > +		return -ENOMEM;
>> > +
>> >  	/* reshape IOs share pages from .devs[0].bio */
>> >  	pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
>> >  
>> > @@ -4635,11 +4636,13 @@ static int handle_reshape_read_error(struct mddev *mddev,
>> >  			/* couldn't read this block, must give up */
>> >  			set_bit(MD_RECOVERY_INTR,
>> >  				&mddev->recovery);
>> > +			kfree(r10b);
>> >  			return -EIO;
>> >  		}
>> >  		sectors -= s;
>> >  		idx++;
>> >  	}
>> > +	kfree(r10b);
>> >  	return 0;
>> >  }
>> >  

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Re: [PATCH] md: raid10: remove VLAIS

[Shaohua Li]

On Fri, Oct 06, 2017 at 01:22:12PM +1100, Neil Brown wrote:
> On Thu, Oct 05 2017, Matthias Kaehlcke wrote:
> 
> > Hi Neil,
> >
> > El Fri, Oct 06, 2017 at 10:58:59AM +1100 NeilBrown ha dit:
> >
> >> On Thu, Oct 05 2017, Matthias Kaehlcke wrote:
> >> 
> >> > The raid10 driver can't be built with clang since it uses a variable
> >> > length array in a structure (VLAIS):
> >> >
> >> > drivers/md/raid10.c:4583:17: error: fields must have a constant size:
> >> >   'variable length array in structure' extension will never be supported
> >> >
> >> > Allocate the r10bio struct with kmalloc instead of using the VLAIS
> >> > construct.
> >> >
> >> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> >> > ---
> >> >  drivers/md/raid10.c | 13 ++++++++-----
> >> >  1 file changed, 8 insertions(+), 5 deletions(-)
> >> >
> >> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> >> > index 374df5796649..9616163eaf8c 100644
> >> > --- a/drivers/md/raid10.c
> >> > +++ b/drivers/md/raid10.c
> >> > @@ -4578,15 +4578,16 @@ static int handle_reshape_read_error(struct mddev *mddev,
> >> >  	/* Use sync reads to get the blocks from somewhere else */
> >> >  	int sectors = r10_bio->sectors;
> >> >  	struct r10conf *conf = mddev->private;
> >> > -	struct {
> >> > -		struct r10bio r10_bio;
> >> > -		struct r10dev devs[conf->copies];
> >> > -	} on_stack;
> >> > -	struct r10bio *r10b = &on_stack.r10_bio;
> >> > +	struct r10bio *r10b;
> >> >  	int slot = 0;
> >> >  	int idx = 0;
> >> >  	struct page **pages;
> >> >  
> >> > +	r10b = kmalloc(sizeof(*r10b) +
> >> > +	       sizeof(struct r10dev) * conf->copies, GFP_KERNEL);
> >> 
> >> GFP_KERNEL isn't a good idea here.
> >> This could wait for writeback, and if writeback tries to write to the
> >> region of the array which is being reshaped, it might deadlock.
> >> 
> >> GFP_NOIO is safer.
> >
> > Good point, thanks!
> >
> >> given that conf->copies is almost always 2 it might be nicer to
> >> have
> >> 
> >> 	struct {
> >> 		struct r10bio r10_bio;
> >> 		struct r10dev devs[2];
> >> 	} on_stack;
> >> 
> >>         struct r10bio *r10b;
> >> 
> >> 	if (conf->copies <= ARRAY_SIZE(on_stack.devs))
> >>         	r10b = &on_stack.r10_bio;
> >>         else
> >>         	r10b = kmalloc(sizeof(*r10b) +
> >> 			       sizeof(struct r10dev) * conf->copies, GFP_NOIO);
> >
> > It would add also add an extra condition to determine if r10b needs to
> > be freed or not.
> 
> True.
> 
> >
> > Given that array reshaping is a rare operation and an error during
> > this operation is an exceptional condition I think the simpler code
> > with always dynamic allocation is preferable. That said I'm fine with
> > reworking the patch according to your suggestion if you or Shaohua
> > prefer it.
> 
> I don't feel strongly about it.  As long as the GFP_KERNEL->GFP_NOIO
> change happens I'm OK with this patch.

Let's use GFP_NOIO then, should not be big deal. I updated the patch.

Thanks,
Shaohua