On 2019/11/26 17:34, Ritesh Harjani wrote: > Hello Damien, > > IIUC, you are trying to fix a stale data read by DIO read for the case > you explained in your patch w.r.t. DIO-write forced to write as buffIO. > > Coincidentally I was just looking at the same code path just now. > So I do have a query to you/f2fs group. Below could be silly one, as I > don't understand F2FS in great detail. > > How is the stale data by DIO read, is protected against a mmap > writes via f2fs_vm_page_mkwrite? > > f2fs_vm_page_mkwrite() f2fs_direct_IO (read) > filemap_write_and_wait_range() > -> f2fs_get_blocks() > -> submit_bio() > > -> set_page_dirty() > > Is above race possible with current f2fs code? > i.e. f2fs_direct_IO could read the stale data from the blocks > which were allocated due to mmap fault? The faulted page is locked until the fault is fully processed so direct IO has to wait for that to complete first. > > Am I missing something here? > > -ritesh > > On 11/26/19 1:27 PM, Damien Le Moal wrote: >> f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT >> flag for a kiocb structure. However, the file system direct IO handler >> function f2fs_direct_IO() may have decided that a direct IO has to be >> exececuted as a buffered IO using the function f2fs_force_buffered_io(). >> This is the case for instance for volumes including zoned block device >> and for unaligned write IOs with LFS mode enabled. >> >> These 2 different methods of identifying direct IOs can result in >> inconsistencies generating stale data access for direct reads after a >> direct IO write that is treated as a buffered write. Fix this >> inconsistency by combining the IOCB_DIRECT flag test with the result >> of f2fs_force_buffered_io(). >> >> Reported-by: Javier Gonzalez <javier@xxxxxxxxxxx> >> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx> >> --- >> fs/f2fs/data.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >> index 5755e897a5f0..8ac2d3b70022 100644 >> --- a/fs/f2fs/data.c >> +++ b/fs/f2fs/data.c >> @@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >> int flag; >> int err = 0; >> bool direct_io = iocb->ki_flags & IOCB_DIRECT; >> + bool do_direct_io = direct_io && >> + !f2fs_force_buffered_io(inode, iocb, from); >> >> /* convert inline data for Direct I/O*/ >> if (direct_io) { >> @@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >> return err; >> } >> >> - if (direct_io && allow_outplace_dio(inode, iocb, from)) >> + if (do_direct_io && allow_outplace_dio(inode, iocb, from)) >> return 0; >> >> if (is_inode_flag_set(inode, FI_NO_PREALLOC)) >> > > -- Damien Le Moal Western Digital Research