* Re: generic_make_request not locked
[not found] <tencent_0BD3EAC403C9DFE43143959B@qq.com>
@ 2013-04-30 6:08 ` Jens Axboe
0 siblings, 0 replies; only message in thread
From: Jens Axboe @ 2013-04-30 6:08 UTC (permalink / raw)
To: remaper; +Cc: linux-fsdevel, linux-kernel
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
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