linux-kernel - Re: [PATCH 4/6] sysfs: use sysfs_lock to protect the sysfs

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Message-ID: <20070530133329.4a10a892@gondolin.boeblingen.de.ibm.com>
Date:	Wed, 30 May 2007 13:33:29 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	gregkh@...e.de, dmitry.torokhov@...il.com, oneukum@...e.de,
	rpurdie@...ys.net, stern@...land.harvard.edu, maneesh@...ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] sysfs: use sysfs_lock to protect the sysfs_dirent
 tree

On Tue, 29 May 2007 01:36:27 +0900,
Tejun Heo <htejun@...il.com> wrote:

> @@ -795,6 +822,8 @@ static int sysfs_readdir(struct file * f
>  			i++;
>  			/* fallthrough */
>  		default:
> +			spin_lock(&sysfs_lock);
> +
>  			pos = &parent_sd->s_children;
>  			while (*pos != cursor)
>  				pos = &(*pos)->s_sibling;
> @@ -827,6 +856,8 @@ static int sysfs_readdir(struct file * f
>  			/* put cursor back in */
>  			cursor->s_sibling = *pos;
>  			*pos = cursor;
> +
> +			spin_unlock(&sysfs_lock);
>  	}
>  	return 0;
>  }

Here's the cause of the "sleeping function called" I saw. filldir() is
called under sysfs_lock, but calls copy_to_user()... This means you
can't use sysfs_lock for protection here.
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