linux-kernel - [PATCH RFC] try_module

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Message-Id: <1184140531.4608.16.camel@sebastian.kern.oss.ntt.co.jp>
Date:	Wed, 11 Jul 2007 16:55:31 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	dedekind@...radead.org, linux-kernel@...r.kernel.org
Subject: [PATCH RFC] try_module_get usage

I keep seeing uses of try_module_get(THIS_MODULE) which seem to mimic
the behavior of the former MOD_INC_USE_COUNT. The UBI driver is one
example:

int ubi_get_device_info(int ubi_num, struct ubi_device_info *di)
{
        const struct ubi_device *ubi;

        if (!try_module_get(THIS_MODULE))
                return -ENODEV;

        if (ubi_num < 0 || ubi_num >= UBI_MAX_DEVICES ||
            !ubi_devices[ubi_num]) {
                module_put(THIS_MODULE);
                return -ENODEV;
        }

        ubi = ubi_devices[ubi_num];
        di->ubi_num = ubi->ubi_num;
        di->leb_size = ubi->leb_size;
        di->min_io_size = ubi->min_io_size;
        di->ro_mode = ubi->ro_mode;
        di->cdev = MKDEV(ubi->major, 0);
        module_put(THIS_MODULE);
        return 0;
}

My understanding is that this is not completely safe (we could be
preempted before try_modules_get gets executed) and that it is the
caller who should manipulate the refcounts. Am I missing something here?

Thank you in advance.

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