On Mon, Apr 23 2018, Amir Goldstein wrote:
> tmpfs uses the helper d_find_alias() to find a dentry from a decoded
> inode, but d_find_alias() skips unhashed dentries, so unlinked files
> cannot be decoded from a file handle.
>
> This can be reproduced using xfstests test program open_by_handle:
> $ open_by handle -c /tmp/testdir
> $ open_by_handle -dk /tmp/testdir
> open_by_handle(/tmp/testdir/file000000) returned 116 incorrectly on an
> unlinked open file!
>
> To fix this, if d_find_alias() can't find a hashed alias, call
> d_find_any_alias() to return an unhashed one.
>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Reviewed-by: NeilBrown <neilb@xxxxxxxx>
Looks reasonable to me. You could possibly just use d_find_any_alias()
unconditionally, but there is sometimes a small benefit in getting a
hashed aliases if there is one.
Thanks,
NeilBrown
> ---
>
> Hi Andrew,
>
> I was nudging Hugh over at LSF/MM about this patch and he has
> suggested that I send it to you, because he has no idea about the
> exportfs parts.
>
> The test for decoding a file handle of an unlinked file has already
> been merged to xfstest generic/467 and the test is failing on tmpfs
> without this change.
>
> Can you please take this patch.
>
> Thanks,
> Amir.
>
> mm/shmem.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 07a1d22807be..5d3fa4099f54 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3404,6 +3404,15 @@ static int shmem_match(struct inode *ino, void *vfh)
> return ino->i_ino == inum && fh[0] == ino->i_generation;
> }
>
> +/* Find any alias of inode, but prefer a hashed alias */
> +static struct dentry *shmem_find_alias(struct inode *inode)
> +{
> + struct dentry *alias = d_find_alias(inode);
> +
> + return alias ?: d_find_any_alias(inode);
> +}
> +
> +
> static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
> struct fid *fid, int fh_len, int fh_type)
> {
> @@ -3420,7 +3429,7 @@ static struct dentry *shmem_fh_to_dentry(struct
> super_block *sb,
> inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
> shmem_match, fid->raw);
> if (inode) {
> - dentry = d_find_alias(inode);
> + dentry = shmem_find_alias(inode);
> iput(inode);
> }
>
> --
> 2.7.4
Attachment:
signature.asc
Description: PGP signature
