'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES = 4 as a maximum. So there
is no real point to allocate the 'entries' pointers array with a dedicate
memory allocation.
Using a flexible array for struct udp_tunnel_nic->entries avoids the
overhead of an additional memory allocation.
This also saves an indirection when the array is accessed.
Finally, __counted_by() can be used for run-time bounds checking if
configured and supported by the compiler.
Signed-off-by: Christophe JAILLET <[email protected]>
---
net/ipv4/udp_tunnel_nic.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
index 029219749785..b6d2d16189c0 100644
--- a/net/ipv4/udp_tunnel_nic.c
+++ b/net/ipv4/udp_tunnel_nic.c
@@ -47,7 +47,7 @@ struct udp_tunnel_nic {
unsigned int n_tables;
unsigned long missed;
- struct udp_tunnel_nic_table_entry **entries;
+ struct udp_tunnel_nic_table_entry *entries[] __counted_by(n_tables);
};
/* We ensure all work structs are done using driver state, but not the code.
@@ -725,16 +725,12 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
struct udp_tunnel_nic *utn;
unsigned int i;
- utn = kzalloc(sizeof(*utn), GFP_KERNEL);
+ utn = kzalloc(struct_size(utn, entries, n_tables), GFP_KERNEL);
if (!utn)
return NULL;
utn->n_tables = n_tables;
INIT_WORK(&utn->work, udp_tunnel_nic_device_sync_work);
- utn->entries = kmalloc_array(n_tables, sizeof(void *), GFP_KERNEL);
- if (!utn->entries)
- goto err_free_utn;
-
for (i = 0; i < n_tables; i++) {
utn->entries[i] = kcalloc(info->tables[i].n_entries,
sizeof(*utn->entries[i]), GFP_KERNEL);
@@ -747,8 +743,6 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
err_free_prev_entries:
while (i--)
kfree(utn->entries[i]);
- kfree(utn->entries);
-err_free_utn:
kfree(utn);
return NULL;
}
@@ -759,7 +753,6 @@ static void udp_tunnel_nic_free(struct udp_tunnel_nic *utn)
for (i = 0; i < utn->n_tables; i++)
kfree(utn->entries[i]);
- kfree(utn->entries);
kfree(utn);
}
--
2.34.1
Christophe JAILLET wrote:
> 'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES = 4 as a maximum. So there
> is no real point to allocate the 'entries' pointers array with a dedicate
> memory allocation.
>
> Using a flexible array for struct udp_tunnel_nic->entries avoids the
> overhead of an additional memory allocation.
>
> This also saves an indirection when the array is accessed.
>
> Finally, __counted_by() can be used for run-time bounds checking if
> configured and supported by the compiler.
>
> Signed-off-by: Christophe JAILLET <[email protected]>
> ---
> net/ipv4/udp_tunnel_nic.c | 11 ++---------
> 1 file changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
> index 029219749785..b6d2d16189c0 100644
> --- a/net/ipv4/udp_tunnel_nic.c
> +++ b/net/ipv4/udp_tunnel_nic.c
> @@ -47,7 +47,7 @@ struct udp_tunnel_nic {
>
> unsigned int n_tables;
> unsigned long missed;
> - struct udp_tunnel_nic_table_entry **entries;
> + struct udp_tunnel_nic_table_entry *entries[] __counted_by(n_tables);
> };
>
> /* We ensure all work structs are done using driver state, but not the code.
> @@ -725,16 +725,12 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
> struct udp_tunnel_nic *utn;
> unsigned int i;
>
> - utn = kzalloc(sizeof(*utn), GFP_KERNEL);
> + utn = kzalloc(struct_size(utn, entries, n_tables), GFP_KERNEL);
> if (!utn)
> return NULL;
> utn->n_tables = n_tables;
Should utn->n_tables be initialized before first use of
struct_size(utn, entries, n_tables)?
Le 24/09/2023 à 18:00, Willem de Bruijn a écrit :
> Christophe JAILLET wrote:
>> 'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES = 4 as a maximum. So there
>> is no real point to allocate the 'entries' pointers array with a dedicate
>> memory allocation.
>>
>> Using a flexible array for struct udp_tunnel_nic->entries avoids the
>> overhead of an additional memory allocation.
>>
>> This also saves an indirection when the array is accessed.
>>
>> Finally, __counted_by() can be used for run-time bounds checking if
>> configured and supported by the compiler.
>>
>> Signed-off-by: Christophe JAILLET <[email protected]>
>> ---
>> net/ipv4/udp_tunnel_nic.c | 11 ++---------
>> 1 file changed, 2 insertions(+), 9 deletions(-)
>>
>> diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
>> index 029219749785..b6d2d16189c0 100644
>> --- a/net/ipv4/udp_tunnel_nic.c
>> +++ b/net/ipv4/udp_tunnel_nic.c
>> @@ -47,7 +47,7 @@ struct udp_tunnel_nic {
>>
>> unsigned int n_tables;
>> unsigned long missed;
>> - struct udp_tunnel_nic_table_entry **entries;
>> + struct udp_tunnel_nic_table_entry *entries[] __counted_by(n_tables);
>> };
>>
>> /* We ensure all work structs are done using driver state, but not the code.
>> @@ -725,16 +725,12 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
>> struct udp_tunnel_nic *utn;
>> unsigned int i;
>>
>> - utn = kzalloc(sizeof(*utn), GFP_KERNEL);
>> + utn = kzalloc(struct_size(utn, entries, n_tables), GFP_KERNEL);
>> if (!utn)
>> return NULL;
>> utn->n_tables = n_tables;
>
> Should utn->n_tables be initialized before first use of
> struct_size(utn, entries, n_tables)?
>
It can't be.
struct_size() is used to compute the memory size to allocate.
Before the kzalloc() call, utn does not exist, so we can't write
anything to utn->n_tables. It is undefined at this point.
It is initialized the line just after, after the allocation, but before
any use.
CJ
On Mon, Sep 25, 2023 at 6:26 PM Christophe JAILLET
<[email protected]> wrote:
>
> Le 24/09/2023 à 18:00, Willem de Bruijn a écrit :
> > Christophe JAILLET wrote:
> >> 'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES = 4 as a maximum. So there
> >> is no real point to allocate the 'entries' pointers array with a dedicate
> >> memory allocation.
> >>
> >> Using a flexible array for struct udp_tunnel_nic->entries avoids the
> >> overhead of an additional memory allocation.
> >>
> >> This also saves an indirection when the array is accessed.
> >>
> >> Finally, __counted_by() can be used for run-time bounds checking if
> >> configured and supported by the compiler.
> >>
> >> Signed-off-by: Christophe JAILLET <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
> >> ---
> >> net/ipv4/udp_tunnel_nic.c | 11 ++---------
> >> 1 file changed, 2 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
> >> index 029219749785..b6d2d16189c0 100644
> >> --- a/net/ipv4/udp_tunnel_nic.c
> >> +++ b/net/ipv4/udp_tunnel_nic.c
> >> @@ -47,7 +47,7 @@ struct udp_tunnel_nic {
> >>
> >> unsigned int n_tables;
> >> unsigned long missed;
> >> - struct udp_tunnel_nic_table_entry **entries;
> >> + struct udp_tunnel_nic_table_entry *entries[] __counted_by(n_tables);
> >> };
> >>
> >> /* We ensure all work structs are done using driver state, but not the code.
> >> @@ -725,16 +725,12 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
> >> struct udp_tunnel_nic *utn;
> >> unsigned int i;
> >>
> >> - utn = kzalloc(sizeof(*utn), GFP_KERNEL);
> >> + utn = kzalloc(struct_size(utn, entries, n_tables), GFP_KERNEL);
> >> if (!utn)
> >> return NULL;
> >> utn->n_tables = n_tables;
> >
> > Should utn->n_tables be initialized before first use of
> > struct_size(utn, entries, n_tables)?
> >
>
> It can't be.
> struct_size() is used to compute the memory size to allocate.
>
> Before the kzalloc() call, utn does not exist, so we can't write
> anything to utn->n_tables. It is undefined at this point.
>
> It is initialized the line just after, after the allocation, but before
> any use.
Of course, sorry. I confused __counted_by's reference to a field
member in the struct, with the normal argument passing of struct_size
and flex_array_size.
Hello:
This patch was applied to netdev/net-next.git (main)
by Paolo Abeni <[email protected]>:
On Sun, 24 Sep 2023 10:03:07 +0200 you wrote:
> 'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES = 4 as a maximum. So there
> is no real point to allocate the 'entries' pointers array with a dedicate
> memory allocation.
>
> Using a flexible array for struct udp_tunnel_nic->entries avoids the
> overhead of an additional memory allocation.
>
> [...]
Here is the summary with links:
- [net-next] udp_tunnel: Use flex array to simplify code
https://git.kernel.org/netdev/net-next/c/ef35bed6fad6
You are awesome, thank you!
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