Re: Patch "nilfs2: make superblock data array index computation sparse friendly" has been added to the 6.9-stable tree

[Greg KH <greg@kroah.com>]

On Mon, May 27, 2024 at 09:53:45AM +0900, Ryusuke Konishi wrote:
> On Mon, May 27, 2024 at 2:21 AM Sasha Levin wrote:
> >
> > This is a note to let you know that I've just added the patch titled
> >
> >     nilfs2: make superblock data array index computation sparse friendly
> >
> > to the 6.9-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> >
> > The filename of the patch is:
> >      nilfs2-make-superblock-data-array-index-computation-.patch
> > and it can be found in the queue-6.9 subdirectory.
> >
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> >
> >
> >
> > commit 5017482ff3b29550015cce7f81279dc69aefd6fe
> > Author: Ryusuke Konishi <konishi.ryusuke@gmail.com>
> > Date:   Tue Apr 30 17:00:19 2024 +0900
> >
> >     nilfs2: make superblock data array index computation sparse friendly
> >
> >     [ Upstream commit 91d743a9c8299de1fc1b47428d8bb4c85face00f ]
> >
> >     Upon running sparse, "warning: dubious: x & !y" is output at an array
> >     index calculation within nilfs_load_super_block().
> >
> >     The calculation is not wrong, but to eliminate the sparse warning, replace
> >     it with an equivalent calculation.
> >
> >     Also, add a comment to make it easier to understand what the unintuitive
> >     array index calculation is doing and whether it's correct.
> >
> >     Link: https://lkml.kernel.org/r/20240430080019.4242-3-konishi.ryusuke@gmail.com
> >     Fixes: e339ad31f599 ("nilfs2: introduce secondary super block")
> >     Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
> >     Cc: Bart Van Assche <bvanassche@acm.org>
> >     Cc: Jens Axboe <axboe@kernel.dk>
> >     Cc: kernel test robot <lkp@intel.com>
> >     Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >     Signed-off-by: Sasha Levin <sashal@kernel.org>
> >
> > diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
> > index 2ae2c1bbf6d17..adbc6e87471ab 100644
> > --- a/fs/nilfs2/the_nilfs.c
> > +++ b/fs/nilfs2/the_nilfs.c
> > @@ -592,7 +592,7 @@ static int nilfs_load_super_block(struct the_nilfs *nilfs,
> >         struct nilfs_super_block **sbp = nilfs->ns_sbp;
> >         struct buffer_head **sbh = nilfs->ns_sbh;
> >         u64 sb2off, devsize = bdev_nr_bytes(nilfs->ns_bdev);
> > -       int valid[2], swp = 0;
> > +       int valid[2], swp = 0, older;
> >
> >         if (devsize < NILFS_SEG_MIN_BLOCKS * NILFS_MIN_BLOCK_SIZE + 4096) {
> >                 nilfs_err(sb, "device size too small");
> > @@ -648,9 +648,25 @@ static int nilfs_load_super_block(struct the_nilfs *nilfs,
> >         if (swp)
> >                 nilfs_swap_super_block(nilfs);
> >
> > +       /*
> > +        * Calculate the array index of the older superblock data.
> > +        * If one has been dropped, set index 0 pointing to the remaining one,
> > +        * otherwise set index 1 pointing to the old one (including if both
> > +        * are the same).
> > +        *
> > +        *  Divided case             valid[0]  valid[1]  swp  ->  older
> > +        *  -------------------------------------------------------------
> > +        *  Both SBs are invalid        0         0       N/A (Error)
> > +        *  SB1 is invalid              0         1       1         0
> > +        *  SB2 is invalid              1         0       0         0
> > +        *  SB2 is newer                1         1       1         0
> > +        *  SB2 is older or the same    1         1       0         1
> > +        */
> > +       older = valid[1] ^ swp;
> > +
> >         nilfs->ns_sbwcount = 0;
> >         nilfs->ns_sbwtime = le64_to_cpu(sbp[0]->s_wtime);
> > -       nilfs->ns_prot_seq = le64_to_cpu(sbp[valid[1] & !swp]->s_last_seq);
> > +       nilfs->ns_prot_seq = le64_to_cpu(sbp[older]->s_last_seq);
> >         *sbpp = sbp[0];
> >         return 0;
> >  }
> 
> This commit fixes the sparse warning output by build "make C=1" with
> the sparse check, but does not fix any operational bugs.
> 
> Therefore, if fixing a harmless sparse warning does not meet the
> requirements for backporting to stable trees (I assume it does),
> please drop it as it is a false positive pickup.  Sorry if the
> "Fixes:" tag is confusing.
> 
> The same goes for the same patch queued to other stable-trees.

Now dropped, thanks!

greg k-h