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.
> 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:
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.
Please see the statx(2) manual page which explains this too.
- Eric
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