On Fri, Jan 07, 2022 at 07:35:56PM -0800, Jaegeuk Kim wrote: > On 01/07, Eric Biggers wrote: > > On Fri, Jan 07, 2022 at 05:52:48PM -0800, Jaegeuk Kim wrote: > > > On 01/07, Eric Biggers wrote: > > > > Hi Jaegeuk, > > > > > > > > On Tue, Jan 04, 2022 at 01:24:16PM -0800, Jaegeuk Kim wrote: > > > > > DIO preallocates physical blocks before writing data, but if an error > > > > > occurrs > > > > > or power-cut happens, we can see block contents from the disk. This > > > > > patch tries > > > > > to fix it by 1) turning to buffered writes for DIO into holes, 2) > > > > > truncating > > > > > unwritten blocks from error or power-cut. > > > > > > > > > > Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org> > > > > > --- > > > > > fs/f2fs/data.c | 5 ++++- > > > > > fs/f2fs/f2fs.h | 5 +++++ > > > > > fs/f2fs/file.c | 27 ++++++++++++++++++--------- > > > > > fs/f2fs/inode.c | 8 ++++++++ > > > > > 4 files changed, 35 insertions(+), 10 deletions(-) > > > > > > > > Unfortunately, this patch doesn't completely fix the uninitialized data > > > > exposure. The problem is that it only makes DIO writes fall back to > > > > buffered > > > > writes for holes, and not for reserved blocks (NEW_ADDR). f2fs's > > > > reserved > > > > blocks are *not* the same as the unwritten extents that other > > > > filesystems have; > > > > f2fs's reserved blocks have to be turned into regular blocks before DIO > > > > can > > > > write to them. That immediately exposes them to concurrent reads (at > > > > least > > > > buffered reads, but I think DIO reads too). > > > > > > Isn't it resolved by i_size which gives the written blocks only? > > > > > > > I'm not sure what you mean, but this is for non-extending writes, so i_size > > isn't relevant. > > Ah, do you mean the file has NEW_ADDR within i_size? If so, let me continue > to investigate further based on the current -dev, as it's quite hard to remove > the old commits. >
Yes, "NEW_ADDR within i_size" is the intended result of fallocate() on f2fs, right? The problem is that DIO writes convert the NEW_ADDR blocks to real blocks, which makes uninitialized data immediately visible to reads before the write actually happens. - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
