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

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Message-ID: <465D800B.2050502@gmail.com>
Date:	Wed, 30 May 2007 22:45:47 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Cornelia Huck <cornelia.huck@...ibm.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

Cornelia Huck wrote:
> 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.

Ouch, right.  I think we can get away with a temp buffer there.  Thanks.

-- 
tejun
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