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[156.34.49.251]) by smtp.gmail.com with ESMTPSA id r6sm3116546qkm.42.2019.05.10.11.07.20 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 10 May 2019 11:07:20 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hP9vT-0006hn-NV; Fri, 10 May 2019 15:07:19 -0300 Date: Fri, 10 May 2019 15:07:19 -0300 From: Jason Gunthorpe To: "santosh.shilimkar@oracle.com" Cc: netdev@vger.kernel.org, davem@davemloft.net, Hans Westgaard Ry Subject: Re: [net-next][PATCH v2 1/2] rds: handle unsupported rdma request to fs dax memory Message-ID: <20190510180719.GD13038@ziepe.ca> References: <1556581040-4812-1-git-send-email-santosh.shilimkar@oracle.com> <1556581040-4812-2-git-send-email-santosh.shilimkar@oracle.com> <20190510125431.GA15434@ziepe.ca> <8b00b41c-bbc5-7584-e5cf-519b0d9100c5@oracle.com> <20190510175538.GB13038@ziepe.ca> <9b0e6760-b684-c1ce-6bf5-738eff325240@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9b0e6760-b684-c1ce-6bf5-738eff325240@oracle.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, May 10, 2019 at 11:02:35AM -0700, santosh.shilimkar@oracle.com wrote: > > > On 5/10/19 10:55 AM, Jason Gunthorpe wrote: > > On Fri, May 10, 2019 at 09:11:24AM -0700, Santosh Shilimkar wrote: > > > On 5/10/2019 5:54 AM, Jason Gunthorpe wrote: > > > > On Mon, Apr 29, 2019 at 04:37:19PM -0700, Santosh Shilimkar wrote: > > > > > From: Hans Westgaard Ry > > > > > > > > > > RDS doesn't support RDMA on memory apertures that require On Demand > > > > > Paging (ODP), such as FS DAX memory. User applications can try to use > > > > > RDS to perform RDMA over such memories and since it doesn't report any > > > > > failure, it can lead to unexpected issues like memory corruption when > > > > > a couple of out of sync file system operations like ftruncate etc. are > > > > > performed. > > > > > > > > This comment doesn't make any sense.. > > > > > > > > > The patch adds a check so that such an attempt to RDMA to/from memory > > > > > apertures requiring ODP will fail. > > > > > > > > > > Reviewed-by: Håkon Bugge > > > > > Reviewed-tested-by: Zhu Yanjun > > > > > Signed-off-by: Hans Westgaard Ry > > > > > Signed-off-by: Santosh Shilimkar > > > > > net/rds/rdma.c | 5 +++-- > > > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/net/rds/rdma.c b/net/rds/rdma.c > > > > > index 182ab84..e0a6b72 100644 > > > > > +++ b/net/rds/rdma.c > > > > > @@ -158,8 +158,9 @@ static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages, > > > > > { > > > > > int ret; > > > > > - ret = get_user_pages_fast(user_addr, nr_pages, write, pages); > > > > > - > > > > > + /* get_user_pages return -EOPNOTSUPP for fs_dax memory */ > > > > > + ret = get_user_pages_longterm(user_addr, nr_pages, > > > > > + write, pages, NULL); > > > > > > > > GUP is supposed to fully work on DAX filesystems. > > > > > > > Above comment has typo. Should have been > > > get_user_pages_longterm return -EOPNOTSUPP. > > > > > > > You only need to switch to the long term version if the duration of > > > > the GUP is under control of user space - ie it may last forever. > > > > > > > > Short duration pins in the kernel do not need long term. > > > > > > > Thats true but the intention here is to use the long term version > > > which does check for the FS DAX memory. Instead of calling direct > > > accessor to check DAX memory region, longterm version of the API > > > is used > > > > > > > At a minimum the commit message needs re-writing to properly explain > > > > the motivation here. > > > > > > > Commit is actually trying to describe the motivation describing more of > > > issues of not making the call fail. The code comment typo was > > > misleading. > > > > Every single sentence in the commit message is wrong > > > I will rewrite commit message but can you please comment on other > questions above. GUP long term was used to detect whether its > fs_dax memory which could be misleading since the RDS MRs are > short lived. Do you want us to use accessor instead to check > if its FS DAX memory? Why would you need to detect FS DAX memory? GUP users are not supposed to care. GUP is supposed to work just 'fine' - other than the usual bugs we have with GUP and any FS backed memory. Jason