On Wed, Sep 11, 2024 at 11:06:22AM +0800, Chao Yu wrote:
> On 2024/9/11 1:06, Eric Biggers wrote:
> > On Tue, Sep 10, 2024 at 08:57:53PM +0800, Chao Yu via Linux-f2fs-devel
> > wrote:
> > > After commit 5c8764f8679e ("f2fs: fix to force buffered IO on inline_data
> > > inode"), f2fs starts to force using buffered IO on inline_data inode.
> > >
> > > And also, it will cause f2fs_getattr() returning invalid zeroed value on
> > > .dio_mem_align and .dio_offset_align fields, however, STATX_DIOALIGN flag
> > > was been tagged. User may use zeroed .stx_dio_offset_align value
> > > since STATX_DIOALIGN was been tagged, then it causes a deadloop during
> > > generic/465 test due to below logic:
> > >
> > > align=stx_dio_offset_align(it equals to zero)
> > > page_size=4096
> > > while [ $align -le $page_size ]; do
> > > echo "$AIO_TEST -a $align -d $testfile.$align" >> $seqres.full
> > > $AIO_TEST -a $align -d $testfile.$align 2>&1 | tee -a $seqres.full
> > > align=$((align * 2))
> > > done
> > >
> > > Quoted from description of statx manual:
> > >
> > > " If a filesystem does not support a field or if it has an
> > > unrepresentable value (for instance, a file with an exotic type),
> > > then the mask bit corresponding to that field will be cleared in
> > > stx_mask even if the user asked for it and a dummy value will be
> > > filled in for compatibility purposes if one is available (e.g.,
> > > a dummy UID and GID may be specified to mount under some
> > > circumstances)."
> > >
> > > We should not set STATX_DIOALIGN flag in kstat.stx_mask if inode
> > > does not support DIO, so that it can indicate related fields contain
> > > dummy value, and avoid following incorrect use of them.
> > >
> > > Fixes: c8c02272a9f7 ("f2fs: support STATX_DIOALIGN")
> >
> > When claiming to be Fixing a commit, please make sure to Cc the author of
> > that
> > commit.
>
> No problem, will make sure they were Cced.
>
> >
> > > Signed-off-by: Chao Yu <c...@kernel.org>
> > > ---
> > > fs/f2fs/file.c | 11 ++++-------
> > > 1 file changed, 4 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > index 99903eafa7fe..f0b8b77e93ba 100644
> > > --- a/fs/f2fs/file.c
> > > +++ b/fs/f2fs/file.c
> > > @@ -906,14 +906,11 @@ int f2fs_getattr(struct mnt_idmap *idmap, const
> > > struct path *path,
> > > * f2fs sometimes supports DIO reads but not DIO writes.
> > > STATX_DIOALIGN
> > > * cannot represent that, so in that case we report no DIO
> > > support.
> > > */
> > > - if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode)) {
> > > - unsigned int bsize = i_blocksize(inode);
> > > -
> > > + if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode) &&
> > > + !f2fs_force_buffered_io(inode, WRITE)) {
> > > + stat->dio_mem_align = F2FS_BLKSIZE;
> > > + stat->dio_offset_align = F2FS_BLKSIZE;
> > > stat->result_mask |= STATX_DIOALIGN;
> > > - if (!f2fs_force_buffered_io(inode, WRITE)) {
> > > - stat->dio_mem_align = bsize;
> > > - stat->dio_offset_align = bsize;
> > > - }
> > > }
> > > flags = fi->i_flags;
> >
> > No, this patch is wrong and the existing code is correct. The cases are:
>
> Yes, you're right, thanks for pointing out this!
>
> >
> > STATX_DIOALIGN set and stx_dio_*_align nonzero:
> > File supports DIO.
> >
> > STATX_DIOALIGN set and stx_dio_*_align zero:
> > File doesn't support DIO.
> >
> > STATX_DIOALIGN unset:
> > Filesystem doesn't support STATX_DIOALIGN, so it's unknown whether
> > the
> > file supports DIO or not.
>
> Above description is clear to me.
>
> >
> > Please see the statx(2) manual page which explains this too.
>
> However, below manual seems not very clear about explaining what does it
> mean about STATX_DIOALIGN is set or not? At least not so clear like above
> description.
>
It just works the same way that the other statx mask bits work. See the
following paragraph:
If a filesystem does not support a field or if it has an unrepresentable
value (for instance, a file with an exotic type), then the mask bit
corresponding to that field will be cleared in stx_mask even if the user
asked for it and a dummy value will be filled in for compatibility purposes
if one is available (e.g., a dummy UID and GID may be specified to mount
under some circumstances).
It might be worth an explicit note in the documentation for stx_dio_mem_align,
but I considered it to be covered by the above.
- Eric
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