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. Thanks, Bernd
