From: Jens Axboe <axboe@kernel.dk>
To: remaper <yp.fangdong@gmail.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: generic_make_request not locked
Date: Tue, 30 Apr 2013 08:08:29 +0200 [thread overview]
Message-ID: <20130430060829.GF9563@kernel.dk> (raw)
In-Reply-To: <tencent_0BD3EAC403C9DFE43143959B@qq.com>
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
parent reply other threads:[~2013-04-30 6:08 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <tencent_0BD3EAC403C9DFE43143959B@qq.com>]
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