diff mbox series

[v4,7/8] net-device: Use new helpers from overflow.h in netdevice APIs

Message ID 20240228204919.3680786-8-andriy.shevchenko@linux.intel.com (mailing list archive)
State New, archived
Headers show
Series iio: core: New macros and making use of them | expand

Commit Message

Andy Shevchenko Feb. 28, 2024, 8:41 p.m. UTC
We have two new helpers struct_size_with_data() and struct_data_pointer()
that we can utilize in alloc_netdev_mqs() and netdev_priv(). Do it so.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 include/linux/netdevice.h |  3 ++-
 net/core/dev.c            | 10 +++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

Comments

Kees Cook Feb. 28, 2024, 9:46 p.m. UTC | #1
On Wed, Feb 28, 2024 at 10:41:37PM +0200, Andy Shevchenko wrote:
> We have two new helpers struct_size_with_data() and struct_data_pointer()
> that we can utilize in alloc_netdev_mqs() and netdev_priv(). Do it so.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  include/linux/netdevice.h |  3 ++-
>  net/core/dev.c            | 10 +++++-----
>  2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index c41019f34179..d046dca18854 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -25,6 +25,7 @@
>  #include <linux/bug.h>
>  #include <linux/delay.h>
>  #include <linux/atomic.h>
> +#include <linux/overflow.h>
>  #include <linux/prefetch.h>
>  #include <asm/cache.h>
>  #include <asm/byteorder.h>
> @@ -2668,7 +2669,7 @@ void dev_net_set(struct net_device *dev, struct net *net)
>   */
>  static inline void *netdev_priv(const struct net_device *dev)
>  {
> -	return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
> +	return struct_data_pointer(dev, NETDEV_ALIGN);
>  }

I really don't like hiding these trailing allocations from the compiler.
Why can't something like this be done (totally untested):


diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 118c40258d07..dae6df4fb177 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2475,6 +2475,8 @@ struct net_device {
 	/** @page_pools: page pools created for this netdevice */
 	struct hlist_head	page_pools;
 #endif
+	u32			priv_size;
+	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
 };
 #define to_net_dev(d) container_of(d, struct net_device, dev)
 
@@ -2665,7 +2667,7 @@ void dev_net_set(struct net_device *dev, struct net *net)
  */
 static inline void *netdev_priv(const struct net_device *dev)
 {
-	return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
+	return dev->priv_data;
 }
 
 /* Set the sysfs physical device reference for the network logical device
diff --git a/net/core/dev.c b/net/core/dev.c
index cb2dab0feee0..afaaa3224656 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10814,18 +10814,14 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 		return NULL;
 	}
 
-	alloc_size = sizeof(struct net_device);
-	if (sizeof_priv) {
-		/* ensure 32-byte alignment of private area */
-		alloc_size = ALIGN(alloc_size, NETDEV_ALIGN);
-		alloc_size += sizeof_priv;
-	}
+	alloc_size = struct_size(p, priv_data, sizeof_priv);
 	/* ensure 32-byte alignment of whole construct */
 	alloc_size += NETDEV_ALIGN - 1;
 
 	p = kvzalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL);
 	if (!p)
 		return NULL;
+	p->priv_size = sizeof_priv;
 
 	dev = PTR_ALIGN(p, NETDEV_ALIGN);
 	dev->padded = (char *)dev - (char *)p;
Andy Shevchenko Feb. 28, 2024, 9:53 p.m. UTC | #2
On Wed, Feb 28, 2024 at 01:46:10PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 10:41:37PM +0200, Andy Shevchenko wrote:

...

> >  static inline void *netdev_priv(const struct net_device *dev)
> >  {
> > -	return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
> > +	return struct_data_pointer(dev, NETDEV_ALIGN);
> >  }
> 
> I really don't like hiding these trailing allocations from the compiler.
> Why can't something like this be done (totally untested):

Below is interesting idea, now at least I started understanding your previous
comments.
Jakub Kicinski Feb. 28, 2024, 10:41 p.m. UTC | #3
On Wed, 28 Feb 2024 13:46:10 -0800 Kees Cook wrote:
> I really don't like hiding these trailing allocations from the compiler.
> Why can't something like this be done (totally untested):
> 
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 118c40258d07..dae6df4fb177 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2475,6 +2475,8 @@ struct net_device {
>  	/** @page_pools: page pools created for this netdevice */
>  	struct hlist_head	page_pools;
>  #endif
> +	u32			priv_size;
> +	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);

I like, FWIW, please submit! :)
Kees Cook Feb. 29, 2024, 12:01 a.m. UTC | #4
On Wed, Feb 28, 2024 at 02:41:48PM -0800, Jakub Kicinski wrote:
> On Wed, 28 Feb 2024 13:46:10 -0800 Kees Cook wrote:
> > I really don't like hiding these trailing allocations from the compiler.
> > Why can't something like this be done (totally untested):
> > 
> > 
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 118c40258d07..dae6df4fb177 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -2475,6 +2475,8 @@ struct net_device {
> >  	/** @page_pools: page pools created for this netdevice */
> >  	struct hlist_head	page_pools;
> >  #endif
> > +	u32			priv_size;
> > +	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> 
> I like, FWIW, please submit! :)

So, I found several cases where struct net_device is included in the
middle of another structure, which makes my proposal more awkward. But I
also don't understand why it's in the _middle_. Shouldn't it always be
at the beginning (with priv stuff following it?)
Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'

struct rtw89_dev
struct ath10k
etc.

Some even have two included (?)

But I still like the idea -- Gustavo has been solving these cases with
having two structs, e.g.:

struct net_device {
	...unchanged...
};

struct net_device_alloc {
	struct net_device	dev;
	u32			priv_size;
	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
};

And internals can use struct net_device_alloc...

-Kees
Gustavo A. R. Silva Feb. 29, 2024, 12:49 a.m. UTC | #5
On 2/28/24 18:01, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 02:41:48PM -0800, Jakub Kicinski wrote:
>> On Wed, 28 Feb 2024 13:46:10 -0800 Kees Cook wrote:
>>> I really don't like hiding these trailing allocations from the compiler.
>>> Why can't something like this be done (totally untested):
>>>
>>>
>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>> index 118c40258d07..dae6df4fb177 100644
>>> --- a/include/linux/netdevice.h
>>> +++ b/include/linux/netdevice.h
>>> @@ -2475,6 +2475,8 @@ struct net_device {
>>>   	/** @page_pools: page pools created for this netdevice */
>>>   	struct hlist_head	page_pools;
>>>   #endif
>>> +	u32			priv_size;
>>> +	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
>>
>> I like, FWIW, please submit! :)
> 
> So, I found several cases where struct net_device is included in the
> middle of another structure, which makes my proposal more awkward. But I
> also don't understand why it's in the _middle_. Shouldn't it always be
> at the beginning (with priv stuff following it?)
> Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'
> 
> struct rtw89_dev
> struct ath10k
> etc.
> 
> Some even have two included (?)
> 
> But I still like the idea -- Gustavo has been solving these cases with
> having two structs, e.g.:
> 
> struct net_device {
> 	...unchanged...
> };
> 
> struct net_device_alloc {
> 	struct net_device	dev;
> 	u32			priv_size;
> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> };
> 
> And internals can use struct net_device_alloc...

Yep, we should really consider going with the above, otherwise we would
have to do something like the following, to avoid having the flexible-array
member nested in the middle of other structs:

struct net_device {
	struct_group_tagged(net_device_hdr, hdr,
		...
		u32			priv_size;
	);
	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
}

We are grouping together the members in `struct net_device`, except the
flexible-array member, into a tagged `struct net_device_hdr`. This allows
us to exclude the flex array from its inclusion in any other struct
that contains `struct net_device` as a member without having to create
a completely separate struct definition.

And let's take as example `struct hfi1_netdev_rx`, where `struct net_device` is
included in the beginning:

drivers/infiniband/hw/hfi1/netdev.h:
struct hfi1_netdev_rx {

-	struct net_device rx_napi;
+       struct net_device_hdr rx_napi;


         struct hfi1_devdata *dd;
         struct hfi1_netdev_rxq *rxq;
         int num_rx_q;
         int rmt_start;
         struct xarray dev_tbl;
         /* count of enabled napi polls */
         atomic_t enabled;
         /* count of netdevs on top */
         atomic_t netdevs;
};

Of course we would also have to update the code that access `struct net_device`
members through `rx_napi` in `struct hfi1_netdev_rx`.

I'm currently working on the above solution for all the cases where having two
separate structs is not currently feasible. And with that we are looking to enable
`-Wflex-array-member-not-at-end`

So, if we can prevent this from the beginning it'd be really great. :)

--
Gustavo
Jakub Kicinski Feb. 29, 2024, 12:56 a.m. UTC | #6
On Wed, 28 Feb 2024 16:01:49 -0800 Kees Cook wrote:
> So, I found several cases where struct net_device is included in the
> middle of another structure, which makes my proposal more awkward. But I
> also don't understand why it's in the _middle_. Shouldn't it always be
> at the beginning (with priv stuff following it?)
> Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'
> 
> struct rtw89_dev
> struct ath10k
> etc.

Ugh, yes, the (ab)use of NAPI.

> Some even have two included (?)

And some seem to be cargo-culted from out-of-tree code and are unused :S

> But I still like the idea -- Gustavo has been solving these cases with
> having two structs, e.g.:
> 
> struct net_device {
> 	...unchanged...
> };
> 
> struct net_device_alloc {
> 	struct net_device	dev;
> 	u32			priv_size;
> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> };
> 
> And internals can use struct net_device_alloc...

That's... less pretty. I'd rather push the ugly into the questionable
users. Make them either allocate the netdev dynamically and store 
a pointer, or move the netdev to the end of the struct.

But yeah, that's a bit of a cleanup :(
Jakub Kicinski Feb. 29, 2024, 12:57 a.m. UTC | #7
On Wed, 28 Feb 2024 18:49:25 -0600 Gustavo A. R. Silva wrote:
> struct net_device {
> 	struct_group_tagged(net_device_hdr, hdr,
> 		...
> 		u32			priv_size;
> 	);
> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> }

No, no, that's not happening.
Gustavo A. R. Silva Feb. 29, 2024, 1:03 a.m. UTC | #8
On 2/28/24 18:57, Jakub Kicinski wrote:
> On Wed, 28 Feb 2024 18:49:25 -0600 Gustavo A. R. Silva wrote:
>> struct net_device {
>> 	struct_group_tagged(net_device_hdr, hdr,
>> 		...
>> 		u32			priv_size;
>> 	);
>> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
>> }
> 
> No, no, that's not happening.

Thanks, one less flex-struct to change. :)
Jakub Kicinski Feb. 29, 2024, 1:15 a.m. UTC | #9
On Wed, 28 Feb 2024 19:03:12 -0600 Gustavo A. R. Silva wrote:
> On 2/28/24 18:57, Jakub Kicinski wrote:
> > On Wed, 28 Feb 2024 18:49:25 -0600 Gustavo A. R. Silva wrote:  
> >> struct net_device {
> >> 	struct_group_tagged(net_device_hdr, hdr,
> >> 		...
> >> 		u32			priv_size;
> >> 	);
> >> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> >> }  
> > 
> > No, no, that's not happening.  
> 
> Thanks, one less flex-struct to change. :)

I like the flex struct.
I don't like struct group around a 360LoC declaration just to avoid
having to fix up a handful of users.
Gustavo A. R. Silva Feb. 29, 2024, 1:36 a.m. UTC | #10
On 2/28/24 19:15, Jakub Kicinski wrote:
> On Wed, 28 Feb 2024 19:03:12 -0600 Gustavo A. R. Silva wrote:
>> On 2/28/24 18:57, Jakub Kicinski wrote:
>>> On Wed, 28 Feb 2024 18:49:25 -0600 Gustavo A. R. Silva wrote:
>>>> struct net_device {
>>>> 	struct_group_tagged(net_device_hdr, hdr,
>>>> 		...
>>>> 		u32			priv_size;
>>>> 	);
>>>> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
>>>> }
>>>
>>> No, no, that's not happening.
>>
>> Thanks, one less flex-struct to change. :)
> 
> I like the flex struct.
> I don't like struct group around a 360LoC declaration just to avoid
> having to fix up a handful of users.

That's what I mean. If we can prevent the flex array ending up in the
middle of a struct by any means, then I wouldn't have to change the
flex struct.

--
Gustavo
Andy Shevchenko Feb. 29, 2024, 10:54 a.m. UTC | #11
On Wed, Feb 28, 2024 at 04:01:49PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 02:41:48PM -0800, Jakub Kicinski wrote:
> > On Wed, 28 Feb 2024 13:46:10 -0800 Kees Cook wrote:

...

> But I still like the idea -- Gustavo has been solving these cases with
> having two structs, e.g.:
> 
> struct net_device {
> 	...unchanged...
> };
> 
> struct net_device_alloc {
> 	struct net_device	dev;
> 	u32			priv_size;
> 	u8			priv_data[] __counted_by(priv_size) __aligned(NETDEV_ALIGN);
> };
> 
> And internals can use struct net_device_alloc...

I just realized that I made same approach in 

f6d7f050e258 ("spi: Don't use flexible array in struct spi_message definition")
75e308ffc4f0 ("spi: Use struct_size() helper")
Kees Cook Feb. 29, 2024, 7:08 p.m. UTC | #12
On Wed, Feb 28, 2024 at 04:56:09PM -0800, Jakub Kicinski wrote:
> On Wed, 28 Feb 2024 16:01:49 -0800 Kees Cook wrote:
> > So, I found several cases where struct net_device is included in the
> > middle of another structure, which makes my proposal more awkward. But I
> > also don't understand why it's in the _middle_. Shouldn't it always be
> > at the beginning (with priv stuff following it?)
> > Quick search and examined manually: git grep 'struct net_device [a-z0-9_]*;'
> > 
> > struct rtw89_dev
> > struct ath10k
> > etc.
> 
> Ugh, yes, the (ab)use of NAPI.
> 
> > Some even have two included (?)
> 
> And some seem to be cargo-culted from out-of-tree code and are unused :S

Ah, which can I remove?

> That's... less pretty. I'd rather push the ugly into the questionable
> users. Make them either allocate the netdev dynamically and store 
> a pointer, or move the netdev to the end of the struct.
> 
> But yeah, that's a bit of a cleanup :(

So far, it's not too bad. I'm doing some test builds now.


As a further aside, this code:

        struct net_device *dev;
	...
        struct net_device *p;
	...
        /* ensure 32-byte alignment of whole construct */
        alloc_size += NETDEV_ALIGN - 1;
        p = kvzalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL);
	...
        dev = PTR_ALIGN(p, NETDEV_ALIGN);

Really screams for a dynamic-sized (bucketed) kmem_cache_alloc
API. Alignment constraints can be described in a regular kmem_cache
allocator (rather than this open-coded version). I've been intending to
build that for struct msg_msg for a while now, and here's another user. :)

-Kees
Jakub Kicinski Feb. 29, 2024, 7:37 p.m. UTC | #13
On Thu, 29 Feb 2024 11:08:58 -0800 Kees Cook wrote:
> > And some seem to be cargo-culted from out-of-tree code and are unused :S  
> 
> Ah, which can I remove?

The one in igc.h does not seem to be referenced by anything in the igc
directory. Pretty sure it's unused.

> As a further aside, this code:
> 
>         struct net_device *dev;
> 	...
>         struct net_device *p;
> 	...
>         /* ensure 32-byte alignment of whole construct */
>         alloc_size += NETDEV_ALIGN - 1;
>         p = kvzalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL);
> 	...
>         dev = PTR_ALIGN(p, NETDEV_ALIGN);
> 
> Really screams for a dynamic-sized (bucketed) kmem_cache_alloc
> API. Alignment constraints can be described in a regular kmem_cache
> allocator (rather than this open-coded version). I've been intending to
> build that for struct msg_msg for a while now, and here's another user. :)

TBH I'm not sure why we align it :S
NETDEV_ALIGN is 32B so maybe some old cache aligning thing?
Kees Cook Feb. 29, 2024, 9:31 p.m. UTC | #14
On Thu, Feb 29, 2024 at 11:37:06AM -0800, Jakub Kicinski wrote:
> On Thu, 29 Feb 2024 11:08:58 -0800 Kees Cook wrote:
> > > And some seem to be cargo-culted from out-of-tree code and are unused :S  
> > 
> > Ah, which can I remove?
> 
> The one in igc.h does not seem to be referenced by anything in the igc
> directory. Pretty sure it's unused.

I'll double check. After trying to do a few conversions I really hit
stuff I didn't like, so I took a slightly different approach in the
patch I sent.
diff mbox series

Patch

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c41019f34179..d046dca18854 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -25,6 +25,7 @@ 
 #include <linux/bug.h>
 #include <linux/delay.h>
 #include <linux/atomic.h>
+#include <linux/overflow.h>
 #include <linux/prefetch.h>
 #include <asm/cache.h>
 #include <asm/byteorder.h>
@@ -2668,7 +2669,7 @@  void dev_net_set(struct net_device *dev, struct net *net)
  */
 static inline void *netdev_priv(const struct net_device *dev)
 {
-	return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
+	return struct_data_pointer(dev, NETDEV_ALIGN);
 }
 
 /* Set the sysfs physical device reference for the network logical device
diff --git a/net/core/dev.c b/net/core/dev.c
index 69c3e3613372..80b765bb8ba2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10859,12 +10859,12 @@  struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 		return NULL;
 	}
 
-	alloc_size = sizeof(struct net_device);
-	if (sizeof_priv) {
+	if (sizeof_priv)
 		/* ensure 32-byte alignment of private area */
-		alloc_size = ALIGN(alloc_size, NETDEV_ALIGN);
-		alloc_size += sizeof_priv;
-	}
+		alloc_size = struct_size_with_data(p, NETDEV_ALIGN, sizeof_priv);
+	else
+		alloc_size = sizeof(struct net_device);
+
 	/* ensure 32-byte alignment of whole construct */
 	alloc_size += NETDEV_ALIGN - 1;