linux-kernel - Re: [PATCH 1/2] kernfs: replace the mutex in kernfs_iop

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Date:   Wed, 2 Dec 2020 13:34:10 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Fox Chen <foxhlchen@...il.com>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kernfs: replace the mutex in kernfs_iop_permission
 with a rwlock

Hello,

On Wed, Dec 02, 2020 at 10:58:36PM +0800, Fox Chen wrote:
> @@ -121,7 +121,7 @@ int kernfs_iop_setattr(struct dentry *dentry, struct iattr *iattr)
>  	if (!kn)
>  		return -EINVAL;
>  
> -	mutex_lock(&kernfs_mutex);
> +	write_lock(&kn->iattr_rwlock);
>  	error = setattr_prepare(dentry, iattr);
>  	if (error)
>  		goto out;
> @@ -134,7 +134,7 @@ int kernfs_iop_setattr(struct dentry *dentry, struct iattr *iattr)
>  	setattr_copy(inode, iattr);
>  
>  out:
> -	mutex_unlock(&kernfs_mutex);
> +	write_unlock(&kn->iattr_rwlock);
>  	return error;
>  }

This is putting GFP_KERNEL allocation inside a rwlock. Can you please test
with debug options including LOCKDEP and DEBUG_ATOMIC_SLEEP turned on?

Thanks.

-- 
tejun