[Drbd-dev] Re: [DRBD-cvs] r1743 - in branches/drbd-0.7: . drbd

[Lars Marowsky-Bree]

On 2005-01-31T12:19:21, svn at svn.drbd.org wrote:

> Modified:
>    branches/drbd-0.7/ChangeLog
>    branches/drbd-0.7/drbd.spec.in
>    branches/drbd-0.7/drbd/drbd_actlog.c
>    branches/drbd-0.7/drbd/drbd_compat_wrappers.h
> Log:
> No longer leak of BIOs.

Good goal, but ...

> Modified: branches/drbd-0.7/drbd/drbd_actlog.c
> ===================================================================
> --- branches/drbd-0.7/drbd/drbd_actlog.c	2005-01-31 09:20:39 UTC (rev 1742)
> +++ branches/drbd-0.7/drbd/drbd_actlog.c	2005-01-31 11:19:19 UTC (rev 1743)
> @@ -68,8 +68,6 @@
>  	struct completion event;
>  	int ok;
>  
> -	bio_get(bio);
> -
>  	bio->bi_bdev = mdev->md_bdev;
>  	bio->bi_sector = sector;
>  	bio_add_page(bio, page, size, 0);

I think this is a bug. If you look at the comments in
linux/include/linux/bio.h, you'll find that this is just how the bio is
supposed to be used:

/*
 * get a reference to a bio, so it won't disappear. the intended use is
 * something like:
 *
 * bio_get(bio);
 * submit_bio(rw, bio);
 * if (bio->bi_flags ...)
 *      do_something
 * bio_put(bio);
 *
 * without the bio_get(), it could potentially complete I/O before submit_bio
 * returns. and then bio would be freed memory when if (bio->bi_flags ...)
 * runs
 */
#define bio_get(bio)    atomic_inc(&(bio)->bi_cnt)

The fix I did was not the right way (removing the bio embedding was much
better), but it also wasn't completely wrong.


Sincerely,
    Lars Marowsky-Brée <lmb at suse.de>

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