2018-01-25 02:26:00

by Jia-Ju Bai

Subject: [PATCH] x86: efi: Replace GFP_ATOMIC with GFP_KERNEL in efi_query_variable_store

The function kzalloc here is not called in atomic context.
If nonblocking in efi_query_variable_store is true,
namely it is in atomic context, efi_query_variable_store will return before
this kzalloc is called.
Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
arch/x86/platform/efi/quirks.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 8a99a2e..b6dcb52 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -177,7 +177,7 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
* that by attempting to use more space than is available.
*/
unsigned long dummy_size = remaining_size + 1024;
- void *dummy = kzalloc(dummy_size, GFP_ATOMIC);
+ void *dummy = kzalloc(dummy_size, GFP_KERNEL);

if (!dummy)
return EFI_OUT_OF_RESOURCES;
--
1.7.9.5

2018-01-25 02:50:02

by Joe Perches

Subject: Re: [PATCH] x86: efi: Replace GFP_ATOMIC with GFP_KERNEL in efi_query_variable_store

On Thu, 2018-01-25 at 10:29 +0800, Jia-Ju Bai wrote:
> The function kzalloc here is not called in atomic context.
> If nonblocking in efi_query_variable_store is true,
> namely it is in atomic context, efi_query_variable_store will return before
> this kzalloc is called.
> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>
> This is found by a static analysis tool named DCNS written by myself.
[]
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
[]
> @@ -177,7 +177,7 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
> * that by attempting to use more space than is available.
> */
> unsigned long dummy_size = remaining_size + 1024;
> - void *dummy = kzalloc(dummy_size, GFP_ATOMIC);
> + void *dummy = kzalloc(dummy_size, GFP_KERNEL);

trivially, kzalloc takes a size_t not an unsigned long
and this _could_, though probably doesn't, lose precision.

It might be nicer to convert to size_t where appropriate.

2018-02-13 18:08:07

by Ingo Molnar

Subject: Re: [PATCH] x86: efi: Replace GFP_ATOMIC with GFP_KERNEL in efi_query_variable_store

* Jia-Ju Bai <[email protected]> wrote:

> The function kzalloc here is not called in atomic context.
> If nonblocking in efi_query_variable_store is true,
> namely it is in atomic context, efi_query_variable_store will return before
> this kzalloc is called.
> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>
> This is found by a static analysis tool named DCNS written by myself.
>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> arch/x86/platform/efi/quirks.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index 8a99a2e..b6dcb52 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -177,7 +177,7 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
> * that by attempting to use more space than is available.
> */
> unsigned long dummy_size = remaining_size + 1024;
> - void *dummy = kzalloc(dummy_size, GFP_ATOMIC);
> + void *dummy = kzalloc(dummy_size, GFP_KERNEL);

Looks good to me!

Reviewed-by: Ingo Molnar <[email protected]>

Thanks,

Ingo

2018-02-13 18:42:08

by Ard Biesheuvel

Subject: Re: [PATCH] x86: efi: Replace GFP_ATOMIC with GFP_KERNEL in efi_query_variable_store

On 13 February 2018 at 18:07, Ingo Molnar <[email protected]> wrote:
>
> * Jia-Ju Bai <[email protected]> wrote:
>
>> The function kzalloc here is not called in atomic context.
>> If nonblocking in efi_query_variable_store is true,
>> namely it is in atomic context, efi_query_variable_store will return before
>> this kzalloc is called.
>> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>>
>> This is found by a static analysis tool named DCNS written by myself.
>>
>> Signed-off-by: Jia-Ju Bai <[email protected]>
>> ---
>> arch/x86/platform/efi/quirks.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
>> index 8a99a2e..b6dcb52 100644
>> --- a/arch/x86/platform/efi/quirks.c
>> +++ b/arch/x86/platform/efi/quirks.c
>> @@ -177,7 +177,7 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
>> * that by attempting to use more space than is available.
>> */
>> unsigned long dummy_size = remaining_size + 1024;
>> - void *dummy = kzalloc(dummy_size, GFP_ATOMIC);
>> + void *dummy = kzalloc(dummy_size, GFP_KERNEL);
>
> Looks good to me!
>
> Reviewed-by: Ingo Molnar <[email protected]>
>

Queued in linux-efi/next

Thanks all.