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Date:	Mon, 14 Jul 2014 19:53:19 +0400
From:	Maxim Patlasov <mpatlasov@...allels.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	<fuse-devel@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>,
	Richard Sharpe <realrichardsharpe@...il.com>
Subject: Re: [PATCH] fuse: avoid scheduling while atomic

On 07/04/2014 08:27 PM, Miklos Szeredi wrote:
> Maxim, thanks for the patch.
>
> Here's a reworked one.  While it looks a bit more complicated, its chances of
> being (and remaining) correct are, I think, better, since the region surrounded
> by kmap/kunmap_atomic is trivially non-sleeping.  This patch also removes more
> lines than it adds, as an added bonus.
>
> Please review and test if possible.

The patch looks fine and works well in my tests.

Maxim

>
> Thanks,
> Miklos
>
> ---
>   fs/fuse/dev.c |   51 +++++++++++++++++++++++----------------------------
>   1 file changed, 23 insertions(+), 28 deletions(-)
>
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -643,9 +643,8 @@ struct fuse_copy_state {
>   	unsigned long seglen;
>   	unsigned long addr;
>   	struct page *pg;
> -	void *mapaddr;
> -	void *buf;
>   	unsigned len;
> +	unsigned offset;
>   	unsigned move_pages:1;
>   };
>   
> @@ -666,23 +665,17 @@ static void fuse_copy_finish(struct fuse
>   	if (cs->currbuf) {
>   		struct pipe_buffer *buf = cs->currbuf;
>   
> -		if (!cs->write) {
> -			kunmap_atomic(cs->mapaddr);
> -		} else {
> -			kunmap_atomic(cs->mapaddr);
> +		if (cs->write)
>   			buf->len = PAGE_SIZE - cs->len;
> -		}
>   		cs->currbuf = NULL;
> -		cs->mapaddr = NULL;
> -	} else if (cs->mapaddr) {
> -		kunmap_atomic(cs->mapaddr);
> +	} else if (cs->pg) {
>   		if (cs->write) {
>   			flush_dcache_page(cs->pg);
>   			set_page_dirty_lock(cs->pg);
>   		}
>   		put_page(cs->pg);
> -		cs->mapaddr = NULL;
>   	}
> +	cs->pg = NULL;
>   }
>   
>   /*
> @@ -691,7 +684,7 @@ static void fuse_copy_finish(struct fuse
>    */
>   static int fuse_copy_fill(struct fuse_copy_state *cs)
>   {
> -	unsigned long offset;
> +	struct page *page;
>   	int err;
>   
>   	unlock_request(cs->fc, cs->req);
> @@ -706,14 +699,12 @@ static int fuse_copy_fill(struct fuse_co
>   
>   			BUG_ON(!cs->nr_segs);
>   			cs->currbuf = buf;
> -			cs->mapaddr = kmap_atomic(buf->page);
> +			cs->pg = buf->page;
> +			cs->offset = buf->offset;
>   			cs->len = buf->len;
> -			cs->buf = cs->mapaddr + buf->offset;
>   			cs->pipebufs++;
>   			cs->nr_segs--;
>   		} else {
> -			struct page *page;
> -
>   			if (cs->nr_segs == cs->pipe->buffers)
>   				return -EIO;
>   
> @@ -726,8 +717,8 @@ static int fuse_copy_fill(struct fuse_co
>   			buf->len = 0;
>   
>   			cs->currbuf = buf;
> -			cs->mapaddr = kmap_atomic(page);
> -			cs->buf = cs->mapaddr;
> +			cs->pg = page;
> +			cs->offset = 0;
>   			cs->len = PAGE_SIZE;
>   			cs->pipebufs++;
>   			cs->nr_segs++;
> @@ -740,14 +731,13 @@ static int fuse_copy_fill(struct fuse_co
>   			cs->iov++;
>   			cs->nr_segs--;
>   		}
> -		err = get_user_pages_fast(cs->addr, 1, cs->write, &cs->pg);
> +		err = get_user_pages_fast(cs->addr, 1, cs->write, &page);
>   		if (err < 0)
>   			return err;
>   		BUG_ON(err != 1);
> -		offset = cs->addr % PAGE_SIZE;
> -		cs->mapaddr = kmap_atomic(cs->pg);
> -		cs->buf = cs->mapaddr + offset;
> -		cs->len = min(PAGE_SIZE - offset, cs->seglen);
> +		cs->pg = page;
> +		cs->offset = cs->addr % PAGE_SIZE;
> +		cs->len = min(PAGE_SIZE - cs->offset, cs->seglen);
>   		cs->seglen -= cs->len;
>   		cs->addr += cs->len;
>   	}
> @@ -760,15 +750,20 @@ static int fuse_copy_do(struct fuse_copy
>   {
>   	unsigned ncpy = min(*size, cs->len);
>   	if (val) {
> +		void *pgaddr = kmap_atomic(cs->pg);
> +		void *buf = pgaddr + cs->offset;
> +
>   		if (cs->write)
> -			memcpy(cs->buf, *val, ncpy);
> +			memcpy(buf, *val, ncpy);
>   		else
> -			memcpy(*val, cs->buf, ncpy);
> +			memcpy(*val, buf, ncpy);
> +
> +		kunmap_atomic(pgaddr);
>   		*val += ncpy;
>   	}
>   	*size -= ncpy;
>   	cs->len -= ncpy;
> -	cs->buf += ncpy;
> +	cs->offset += ncpy;
>   	return ncpy;
>   }
>   
> @@ -874,8 +869,8 @@ static int fuse_try_move_page(struct fus
>   out_fallback_unlock:
>   	unlock_page(newpage);
>   out_fallback:
> -	cs->mapaddr = kmap_atomic(buf->page);
> -	cs->buf = cs->mapaddr + buf->offset;
> +	cs->pg = buf->page;
> +	cs->offset = buf->offset;
>   
>   	err = lock_request(cs->fc, cs->req);
>   	if (err)
>

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