Patch "nilfs2: make superblock data array index computation sparse friendly" has been added to the 6.8-stable tree

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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 6.8-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-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 121e12b326da13b8334c2d724c7c6a72a0dc20c5
Author: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
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@xxxxxxxxx
    Fixes: e339ad31f599 ("nilfs2: introduce secondary super block")
    Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
    Cc: Bart Van Assche <bvanassche@xxxxxxx>
    Cc: Jens Axboe <axboe@xxxxxxxxx>
    Cc: kernel test robot <lkp@xxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 71400496ed365..3e3c1d32da180 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;
 }




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