linux-kernel - Re: Question about commit f9a67b1182e5 ("md/bitmap: clear bitmap if bitmap

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Message-ID: <20160913172433.GB24264@kernel.org>
Date:   Tue, 13 Sep 2016 10:24:33 -0700
From:   Shaohua Li <shli@...nel.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        gqjiang@...e.com
Subject: Re: Question about commit f9a67b1182e5 ("md/bitmap: clear bitmap if
 bitmap_create failed").

On Mon, Sep 12, 2016 at 09:09:48PM +0200, Christophe JAILLET wrote:
> Hi,
> 
> I'm puzzled by commit f9a67b1182e5 ("md/bitmap: clear bitmap if
> bitmap_create failed").
Hi Christophe,
Thank you very much to help check this!

> Part of the commit is:
> 
> @@ -1865,8 +1866,10 @@ int bitmap_copy_from_slot(struct mddev *mddev, int
> slot,
>      struct bitmap_counts *counts;
>      struct bitmap *bitmap = bitmap_create(mddev, slot);
> 
> -    if (IS_ERR(bitmap))
> +    if (IS_ERR(bitmap)) {
> +        bitmap_free(bitmap);
>          return PTR_ERR(bitmap);
> +    }
> 
> but if 'bitmap' is an error, I think that bad things will happen in
> 'bitmap_free()' when, at the beginning of the function, we will execute:
> 
>     if (bitmap->sysfs_can_clear) <-----------------
>         sysfs_put(bitmap->sysfs_can_clear);

Add Guoqing.

Yeah, you are right, this bitmap_free isn't required. This must be something
slip in in the v2 patch. I'll delete that line.

> However, the commit log message is really explicit and adding this call to
> 'bitmap_free' has really been done one purpose. ("If bitmap_create returns
> an error, we need to call either bitmap_destroy or bitmap_free to do clean
> up, ...")

this log is a little confusing, I thought it really means the bitmap_free called
in bitmap_create. The V1 patch calls bitmap_destroy in bitmap_create.

Thanks,
Shaohua