On Tue, Sep 25, 2018 at 03:13:30PM +0800, Huang Ying wrote:
> @@ -3487,35 +3521,66 @@ static int __swap_duplicate_locked(struct swap_info_struct *p,
> }
>
> /*
> - * Verify that a swap entry is valid and increment its swap map count.
> + * Verify that the swap entries from *entry is valid and increment their
> + * PMD/PTE swap mapping count.
> *
> * Returns error code in following case.
> * - success -> 0
> * - swp_entry is invalid -> EINVAL
> - * - swp_entry is migration entry -> EINVAL
I'm assuming it wasn't possible to hit this error before this patch, and you're
just removing it now since you're in the area?
> * - swap-cache reference is requested but there is already one. -> EEXIST
> * - swap-cache reference is requested but the entry is not used. -> ENOENT
> * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
> + * - the huge swap cluster has been split. -> ENOTDIR
Strangely intuitive choice of error code :)
> /*
> * Increase reference count of swap entry by 1.
> - * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
> - * but could not be atomically allocated. Returns 0, just as if it succeeded,
> - * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
> - * might occur if a page table entry has got corrupted.
> + *
> + * Return error code in following case.
> + * - success -> 0
> + * - swap_count_continuation is required but could not be atomically allocated.
> + * *entry is used to return swap entry to call add_swap_count_continuation().
> + * -> ENOMEM
> + * - otherwise same as __swap_duplicate()
> */
> -int swap_duplicate(swp_entry_t entry)
> +int swap_duplicate(swp_entry_t *entry, int entry_size)
> {
> int err = 0;
>
> - while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
> - err = add_swap_count_continuation(entry, GFP_ATOMIC);
> + while (!err &&
> + (err = __swap_duplicate(entry, entry_size, 1)) == -ENOMEM)
> + err = add_swap_count_continuation(*entry, GFP_ATOMIC);
> return err;
Now we're returning any error we get from __swap_duplicate, apparently to
accommodate ENOTDIR later in the series, which is a change from the behavior
introduced in 570a335b8e22 ("swap_info: swap count continuations"). This might
belong in a separate patch given its potential for side effects.
Although, I don't understand why 570a335b8e22 ignored errors other than -ENOMEM
when both swap_duplicate callers _seem_ from a quick read to be able to respond
gracefully to any error.
