From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] fuse: Fix race in fuse_writepage_in_flight()
Date: Thu, 10 Jan 2019 13:48:42 +0300 [thread overview]
Message-ID: <00b1782a-5c5c-5bc8-7ea9-4f8450679fa1@virtuozzo.com> (raw)
In-Reply-To: <154322517208.18737.3297786654135648324.stgit@localhost.localdomain>
Hi, Miklos,
any comments about this?
On 26.11.2018 12:46, Kirill Tkhai wrote:
> Checking for FR_PENDING in fuse_writepage_in_flight() is racy.
> It does not guarantee the first request in misc.write.next list
> is not in userspace, since there we take fc->lock, while
> fuse_dev_do_read() takes fiq->waitq.lock:
>
> fuse_dev_read() fuse_writepage_in_flight()
> test_bit(FR_PENDING)
> clear_bit(FR_PENDING)
> handle old_req->pages[0] in userspace
> copy_highpage(old_req->pages[0], page)
> ^^^^^
> userspace never sees this pages
>
> The only reliable way to determ, whether we are able to replace
> old_req's page, is to completely skip the first request in the list.
> This patch makes the function to do that.
>
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
> fs/fuse/file.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index b52f9baaa3e7..c6650c68b31a 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1740,6 +1740,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
> {
> struct fuse_conn *fc = get_fuse_conn(new_req->inode);
> struct fuse_inode *fi = get_fuse_inode(new_req->inode);
> + struct fuse_req *first_req;
> struct fuse_req *tmp;
> struct fuse_req *old_req;
> bool found = false;
> @@ -1764,6 +1765,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
> }
>
> new_req->num_pages = 1;
> + first_req = old_req;
> for (tmp = old_req; tmp != NULL; tmp = tmp->misc.write.next) {
> BUG_ON(tmp->inode != new_req->inode);
> curr_index = tmp->misc.write.in.offset >> PAGE_SHIFT;
> @@ -1773,7 +1775,7 @@ static bool fuse_writepage_in_flight(struct fuse_req *new_req,
> }
> }
>
> - if (old_req->num_pages == 1 && test_bit(FR_PENDING, &old_req->flags)) {
> + if (old_req->num_pages == 1 && old_req != first_req) {
> struct backing_dev_info *bdi = inode_to_bdi(page->mapping->host);
>
> copy_highpage(old_req->pages[0], page);
>
next prev parent reply other threads:[~2019-01-10 10:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-26 9:46 [PATCH 1/2] fuse: Fix race in fuse_writepage_in_flight() Kirill Tkhai
2018-11-26 9:46 ` [PATCH 2/2] fuse: Replace page without copying " Kirill Tkhai
2019-01-15 15:39 ` Miklos Szeredi
2019-01-15 16:14 ` Kirill Tkhai
2019-01-15 16:36 ` Miklos Szeredi
2019-01-15 16:38 ` Kirill Tkhai
2019-01-10 10:48 ` Kirill Tkhai [this message]
2019-01-10 11:00 ` [PATCH 1/2] fuse: Fix race " Miklos Szeredi
2019-01-10 11:03 ` Kirill Tkhai
2019-01-15 15:37 ` Miklos Szeredi
2019-01-15 15:55 ` Kirill Tkhai
2019-01-15 16:03 ` Miklos Szeredi
2019-01-15 16:05 ` Kirill Tkhai
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