linux-kernel - Re: [patch 05/27] fs: brlock vfsmount

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Message-ID: <20090425035040.GW8633@ZenIV.linux.org.uk>
Date:	Sat, 25 Apr 2009 04:50:40 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	npiggin@...e.de
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 05/27] fs: brlock vfsmount_lock

On Sat, Apr 25, 2009 at 11:20:25AM +1000, npiggin@...e.de wrote:

[overall: sane idea, but...]

> +void vfsmount_read_lock(void)
> +{
> +	spinlock_t *lock;
> +
> +	lock = &get_cpu_var(vfsmount_lock);
> +	spin_lock(lock);
> +}
> +
> +void vfsmount_read_unlock(void)
> +{
> +	spinlock_t *lock;
> +
> +	lock = &__get_cpu_var(vfsmount_lock);
> +	spin_unlock(lock);
> +	put_cpu_var(vfsmount_lock);
> +}

These might be hot enough to be worth inlining, at least in fs/namei.c
users.  Or not - really needs testing.

> @@ -68,9 +113,9 @@ static int mnt_alloc_id(struct vfsmount
>  
>  retry:
>  	ida_pre_get(&mnt_id_ida, GFP_KERNEL);
> -	spin_lock(&vfsmount_lock);
> +	vfsmount_write_lock();
>  	res = ida_get_new(&mnt_id_ida, &mnt->mnt_id);
> -	spin_unlock(&vfsmount_lock);
> +	vfsmount_write_unlock();

Yuck.  _Really_ an overkill here.

>  static void mnt_free_id(struct vfsmount *mnt)
>  {
> -	spin_lock(&vfsmount_lock);
> +	vfsmount_write_lock();
>  	ida_remove(&mnt_id_ida, mnt->mnt_id);
> -	spin_unlock(&vfsmount_lock);
> +	vfsmount_write_unlock();
>  }

Ditto.

Missing: description of when we need it for read/when we need it for write.
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