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    SubjectRe: [PATCH 2/2] ext4, dax: set ext4_dax_aops for dax files
    On Tue 11-09-18 11:15:18, Dan Williams wrote:
    > On Tue, Sep 11, 2018 at 8:42 AM, Toshi Kani <toshi.kani@hpe.com> wrote:
    > > Sync syscall to an existing DAX file needs to flush processor cache,
    > > but it does not currently. This is because 'ext4_da_aops' is set to
    > > address_space_operations of existing DAX files, instead of 'ext4_dax_aops',
    > > since S_DAX flag is set after ext4_set_aops() in the open path.
    > >
    > > New file
    > > --------
    > > lookup_open
    > > ext4_create
    > > __ext4_new_inode
    > > ext4_set_inode_flags // Set S_DAX flag
    > > ext4_set_aops // Set aops to ext4_dax_aops
    > >
    > > Existing file
    > > -------------
    > > lookup_open
    > > ext4_lookup
    > > ext4_iget
    > > ext4_set_aops // Set aops to ext4_da_aops
    > > ext4_set_inode_flags // Set S_DAX flag
    > >
    > > Change ext4_iget() to call ext4_set_inode_flags() before ext4_set_aops().
    > >
    > > Fixes: 5f0663bb4a64f588f0a2dd6d1be68d40f9af0086
    >
    > Same format nit:
    >
    > Fixes: 5f0663bb4a64 ("ext4, dax: introduce ext4_dax_aops")
    > Cc: <stable@vger.kernel.org>
    >
    >
    > > Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
    > > Cc: Jan Kara <jack@suse.cz>
    > > Cc: Dan Williams <dan.j.williams@intel.com>
    > > Cc: "Theodore Ts'o" <tytso@mit.edu>
    > > Cc: Andreas Dilger <adilger.kernel@dilger.ca>
    > > ---
    > > fs/ext4/inode.c | 3 ++-
    > > 1 file changed, 2 insertions(+), 1 deletion(-)
    > >
    > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    > > index 775cd9b4af55..93cbbb859c40 100644
    > > --- a/fs/ext4/inode.c
    > > +++ b/fs/ext4/inode.c
    > > @@ -4998,6 +4998,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
    > > if (ret)
    > > goto bad_inode;
    > >
    > > + ext4_set_inode_flags(inode);
    > > +
    >
    > Hmm, does this have unintended behavior changes?
    >
    > I notice that there are some checks for flags "IS_APPEND(inode) ||
    > IS_IMMUTABLE(inode)" *before* the call to ext4_set_inode_flags(). I
    > didn't look too much deeper at whether those checks are bogus, but it
    > would seem safer to do something like this for a lower risk fix.
    >
    > Thoughts?

    Well, safer but it would leave the landmine around for others to hit.
    Toshi, please move the ext4_set_inode_flags() call to be just after the
    assignment:

    ei->i_flags = le32_to_cpu(raw_inode->i_flags);

    in ext4_iget(). That way people won't introduce checks for i_flags that can
    never hit... And yes, it fixes also other bugs (mostly in sanity checks
    AFAICS) than the DAX issue.

    Honza

    >
    > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    > index d0dd585add6a..1e9ab445c777 100644
    > --- a/fs/ext4/inode.c
    > +++ b/fs/ext4/inode.c
    > @@ -4999,7 +4999,6 @@ struct inode *ext4_iget(struct super_block *sb,
    > unsigned long ino)
    > if (S_ISREG(inode->i_mode)) {
    > inode->i_op = &ext4_file_inode_operations;
    > inode->i_fop = &ext4_file_operations;
    > - ext4_set_aops(inode);
    > } else if (S_ISDIR(inode->i_mode)) {
    > inode->i_op = &ext4_dir_inode_operations;
    > inode->i_fop = &ext4_dir_operations;
    > @@ -5042,6 +5041,12 @@ struct inode *ext4_iget(struct super_block *sb,
    > unsigned long ino)
    > }
    > brelse(iloc.bh);
    > ext4_set_inode_flags(inode);
    > + /*
    > + * Now that we have determined whether DAX is enabled, set the
    > + * proper address spaces operations
    > + */
    > + if (S_ISREG(inode->i_mode))
    > + ext4_set_aops(inode);
    >
    > unlock_new_inode(inode);
    > return inode;
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

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