[Devel] Re: [PATCH] Save and restore the [compat_]robust_list member of the task struct.

[Nathan Lynch]

Nathan Lynch <ntl at pobox.com> writes:
> Matt Helsley <matthltc at us.ibm.com> writes:
>> diff --git a/include/linux/futex.h b/include/linux/futex.h
>> index 4326f81..934cf98 100644
>> --- a/include/linux/futex.h
>> +++ b/include/linux/futex.h
>> @@ -185,9 +185,46 @@ union futex_key {
>>  #define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }
>>  
>>  #ifdef CONFIG_FUTEX
>> +extern long do_set_robust_list(struct robust_list_head __user *head, size_t len);
>>  extern void exit_robust_list(struct task_struct *curr);
>>  extern void exit_pi_state_list(struct task_struct *curr);
>>  extern int futex_cmpxchg_enabled;
>> +
>> +#ifdef CONFIG_CHECKPOINT
>> +#include <linux/checkpoint_hdr.h>
>> +
>> +static inline void save_task_robust_futex_list(struct ckpt_hdr_task *h,
>> +					       struct task_struct *t)
>> +{
>> +	/*
>> +	 * These are __user pointers and thus can be saved without
>> +	 * the objhash.
>> +	 */
>> +	h->robust_futex_list = (unsigned long)t->robust_list;
>> +	h->robust_futex_head_len = sizeof(*t->robust_list);
>> +#ifdef CONFIG_COMPAT
>> +	h->compat_robust_futex_list = ptr_to_compat(t->compat_robust_list);
>> +	h->compat_robust_futex_head_len = sizeof(*t->compat_robust_list);
>> +#endif
>> +}
>> +
>> +static inline void restore_task_robust_futex_list(struct ckpt_hdr_task *h)
>> +{
>> +	/* Since we restore the memory map the address remains the same and
>> +	 * this is safe. This is the same as [compat_]sys_set_robust_list() */
>> +	if (h->robust_futex_list) {
>> +		struct robust_list_head __user *rfl = (void __user *)(unsigned long)h->robust_futex_list;
>> +		do_set_robust_list(rfl, h->robust_futex_head_len);
>> +	}
>> +#ifdef CONFIG_COMPAT
>> +	if (h->compat_robust_futex_list) {
>> +		struct compat_robust_list_head __user *crfl = compat_ptr(h->compat_robust_futex_list);
>> +		do_compat_set_robust_list(crfl, h->compat_robust_futex_head_len);
>> +	}
>> +#endif
>> +}
>> +#endif /* CONFIG_CHECKPOINT */
>> +
>>  #else
>>  static inline void exit_robust_list(struct task_struct *curr)
>>  {
>> @@ -195,6 +232,15 @@ static inline void exit_robust_list(struct task_struct *curr)
>>  static inline void exit_pi_state_list(struct task_struct *curr)
>>  {
>>  }
>> +#ifdef CONFIG_CHECKPOINT
>> +static inline void save_task_robust_futex_list(struct ckpt_hdr_task *h,
>> +					      struct task_struct *t)
>> +{
>> +}
>> +static inline void restore_task_robust_futex_list(struct ckpt_hdr_task *h)
>> +{
>> +}
>> +#endif /* CONFIG_CHECKPOINT */
>>  #endif
>>  #endif /* __KERNEL__ */
>>  
>
> powerpc build with CONFIG_CHECKPOINT=y fails.  I suspect any
> CONFIG_COMPAT=y build fails?
>
> In file included from kernel/fork.c:42:
> include/linux/futex.h: In function ‘save_task_robust_futex_list’:
> include/linux/futex.h:206: error: implicit declaration of function ‘ptr_to_compat’
> include/linux/futex.h:207: error: dereferencing pointer to incomplete type
> include/linux/futex.h: In function ‘restore_task_robust_futex_list’:
> include/linux/futex.h:221: error: implicit declaration of function ‘compat_ptr’
> include/linux/futex.h:221: warning: initialization makes pointer from integer without a cast
> include/linux/futex.h:222: error: implicit declaration of function ‘do_compat_set_robust_list’
>
> fix:
>
> diff --git a/include/linux/futex.h b/include/linux/futex.h
> index 934cf98..f40a9bf 100644
> --- a/include/linux/futex.h
> +++ b/include/linux/futex.h
> @@ -3,6 +3,7 @@
>  
>  #include <linux/compiler.h>
>  #include <linux/types.h>
> +#include <linux/compat.h>
>  
>  struct inode;
>  struct mm_struct;

Sigh... this breaks headers_check:

linux-2.6.git/usr/include/linux/futex.h:6: included file 'linux/compat.h' is not exported

I think we could sidestep this mess by putting the futex-related
checkpoint functions in futex.c instead of making them inlines in an
exported header.
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