generic_make_request not locked

generic_make_request not locked

[remaper]

/*
 * We only want one ->make_request_fn to be active at a time,
 * else stack usage with stacked devices could be a problem.
 * So use current->bio_list to keep a list of requests
 * submited by a make_request_fn function.
 * current->bio_list is also used as a flag to say if
 * generic_make_request is currently active in this task or not.
 * If it is NULL, then no make_request is active.  If it is non-NULL,
 * then a make_request is active, and new requests should be added
 * at the tail
 */
void generic_make_request(struct bio *bio)
{
...
    if (current->bio_list) {
        /* make_request is active */
        bio_list_add(current->bio_list, bio);
        return;
    }
...
}

current->bio_list is a global variable, and generic_make_request would run on multithread environment, so, i don't understand why here( bio_list_add ) not lock?
thx everybody.ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: generic_make_request not locked

[Jens Axboe]

On Tue, Apr 30 2013, remaper wrote:
> /*
>  * We only want one ->make_request_fn to be active at a time,
>  * else stack usage with stacked devices could be a problem.
>  * So use current->bio_list to keep a list of requests
>  * submited by a make_request_fn function.
>  * current->bio_list is also used as a flag to say if
>  * generic_make_request is currently active in this task or not.
>  * If it is NULL, then no make_request is active.  If it is non-NULL,
>  * then a make_request is active, and new requests should be added
>  * at the tail
>  */
> void generic_make_request(struct bio *bio)
> {
> ...
>     if (current->bio_list) {
>         /* make_request is active */
>         bio_list_add(current->bio_list, bio);
>         return;
>     }
> ...
> }
> 
> current->bio_list is a global variable, and generic_make_request would
> run on multithread environment, so, i don't understand why here(
> bio_list_add ) not lock?  thx everybody.

'current' refers to the task currently executing task. So
current->bio_list isn't shared, hence there's no need for any locking.

-- 
Jens Axboe