关于generic_make_request上锁的问题

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;
        }
...
}

虽然generic_make_request表明only want one make_request_fn 处于激活状态，但是我没找到这个是怎么保证的。
但是current->bio_list是一个全局的变量，为什么直接bio_list_add都没有加锁呢？

firkraag

in 2.6.34, function generic_make_request(), the comment said:

__generic_make_request may indeed add some more bios through a recursive call to generic_make_request.  If it did, we find a non-NULL value in bio_list and re-enter the loop from the top.  In this case we really did just take the bio of the top of the list (no pretending) and so remove it from bio_list, and call into __generic_make_request again.

remaper

回复 2# firkraag
__generic_xxx() 什么地方会调用 generic_xxx() ？

   

firkraag

回复 3# remaper

for stacked block devices(e.g.  md or dm)

embeddedlwp

回复 4# firkraag


什么是stacked?


   

remaper

回复 4# firkraag

请问能指出代码吗？

firkraag

回复 6# remaper
google "device mapper"