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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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