On Wed, 6 Mar 2024 at 12:16, Bernd Schubert <bernd.schubert@xxxxxxxxxxx> wrote: > > > > On 3/6/24 11:01, Miklos Szeredi wrote: > > On Tue, 29 Aug 2023 at 20:37, Lei Huang <lei.huang@xxxxxxxxxxxxxxx> wrote: > >> > >> Our user space filesystem relies on fuse to provide POSIX interface. > >> In our test, a known string is written into a file and the content > >> is read back later to verify correct data returned. We observed wrong > >> data returned in read buffer in rare cases although correct data are > >> stored in our filesystem. > >> > >> Fuse kernel module calls iov_iter_get_pages2() to get the physical > >> pages of the user-space read buffer passed in read(). The pages are > >> not pinned to avoid page migration. When page migration occurs, the > >> consequence are two-folds. > >> > >> 1) Applications do not receive correct data in read buffer. > >> 2) fuse kernel writes data into a wrong place. > >> > >> Using iov_iter_extract_pages() to pin pages fixes the issue in our > >> test. > >> > >> An auxiliary variable "struct page **pt_pages" is used in the patch > >> to prepare the 2nd parameter for iov_iter_extract_pages() since > >> iov_iter_get_pages2() uses a different type for the 2nd parameter. > >> > >> Signed-off-by: Lei Huang <lei.huang@xxxxxxxxxxxxxxx> > > > > Applied, with a modification to only unpin if > > iov_iter_extract_will_pin() returns true. > > Hi Miklos, > > do you have an idea if this needs to be back ported and to which kernel > version? > I had tried to reproduce data corruption with 4.18 - Lei wrote that he > could see issues with older kernels as well, but I never managed to > trigger anything on 4.18-RHEL. Typically I use ql-fstest > (https://github.com/bsbernd/ql-fstest) and even added random DIO as an > option - nothing report with weeks of run time. I could try again with > more recent kernels that have folios. I don't think that corruption will happen in real life. So I'm not sure we need to bother with backporting, and definitely not before when the infrastructure was introduced. Thanks, Miklos
