The patch titled
Subject: nilfs2: make superblock data array index computation sparse friendly
has been added to the -mm mm-nonmm-unstable branch. Its filename is
nilfs2-make-superblock-data-array-index-computation-sparse-friendly.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-make-superblock-data-array-index-computation-sparse-friendly.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Subject: nilfs2: make superblock data array index computation sparse friendly
Date: Tue, 30 Apr 2024 17:00:19 +0900
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>
---
fs/nilfs2/the_nilfs.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
--- a/fs/nilfs2/the_nilfs.c~nilfs2-make-superblock-data-array-index-computation-sparse-friendly
+++ a/fs/nilfs2/the_nilfs.c
@@ -592,7 +592,7 @@ static int nilfs_load_super_block(struct
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
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;
}
_
Patches currently in -mm which might be from konishi.ryusuke@xxxxxxxxx are
nilfs2-use-integer-type-instead-of-enum-req_op-for-event-tracing-header.patch
nilfs2-make-superblock-data-array-index-computation-sparse-friendly.patch
