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%3Ba=su...

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