Re: [net-next][PATCH v2 1/2] rds: handle unsupported rdma request to fs dax memory
From: Jason Gunthorpe <jgg@ziepe.ca>
Date: 2019-05-10 12:54:36
On Mon, Apr 29, 2019 at 04:37:19PM -0700, Santosh Shilimkar wrote:
From: Hans Westgaard Ry <redacted> 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..
quoted hunk ↗ jump to hunk
The patch adds a check so that such an attempt to RDMA to/from memory apertures requiring ODP will fail. Reviewed-by: Håkon Bugge <redacted> Reviewed-tested-by: Zhu Yanjun [off-list ref] Signed-off-by: Hans Westgaard Ry <redacted> Signed-off-by: Santosh Shilimkar <redacted> 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. 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. At a minimum the commit message needs re-writing to properly explain the motivation here. Jason