[PATCH v6 v6 2/3] ext4: use READ_ONCE/WRITE_ONCE for s_mb_stats
From: Baolin Liu
Date: Sat May 23 2026 - 21:55:44 EST
From: Baolin Liu <liubaolin@xxxxxxxxxx>
Use READ_ONCE()/WRITE_ONCE() for concurrent accesses to
s_mb_stats.
Signed-off-by: Baolin Liu <liubaolin@xxxxxxxxxx>
---
fs/ext4/mballoc.c | 24 ++++++++++++------------
fs/ext4/sysfs.c | 25 ++++++++++++++++++++++++-
2 files changed, 36 insertions(+), 13 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d36b0f7b5d7d..fed6d854877b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -924,7 +924,7 @@ static int ext4_mb_scan_groups_xa_range(struct ext4_allocation_context *ac,
xa_for_each_range(xa, group, grp, start, end - 1) {
int err;
- if (sbi->s_mb_stats)
+ if (READ_ONCE(sbi->s_mb_stats))
atomic64_inc(&sbi->s_bal_cX_groups_considered[cr]);
err = ext4_mb_scan_group(ac, grp->bb_group);
@@ -980,7 +980,7 @@ static int ext4_mb_scan_groups_p2_aligned(struct ext4_allocation_context *ac,
goto wrap_around;
}
- if (sbi->s_mb_stats)
+ if (READ_ONCE(sbi->s_mb_stats))
atomic64_inc(&sbi->s_bal_cX_failed[ac->ac_criteria]);
/* Increment cr and search again if no group is found */
@@ -1031,7 +1031,7 @@ static int ext4_mb_scan_groups_goal_fast(struct ext4_allocation_context *ac,
goto wrap_around;
}
- if (sbi->s_mb_stats)
+ if (READ_ONCE(sbi->s_mb_stats))
atomic64_inc(&sbi->s_bal_cX_failed[ac->ac_criteria]);
/*
* CR_BEST_AVAIL_LEN works based on the concept that we have
@@ -1135,7 +1135,7 @@ static int ext4_mb_scan_groups_best_avail(struct ext4_allocation_context *ac,
/* Reset goal length to original goal length before falling into CR_GOAL_LEN_SLOW */
ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
- if (sbi->s_mb_stats)
+ if (READ_ONCE(sbi->s_mb_stats))
atomic64_inc(&sbi->s_bal_cX_failed[ac->ac_criteria]);
ac->ac_criteria = CR_GOAL_LEN_SLOW;
@@ -1184,7 +1184,7 @@ static int ext4_mb_scan_groups_linear(struct ext4_allocation_context *ac,
ac->ac_criteria++;
/* Processed all groups and haven't found blocks */
- if (sbi->s_mb_stats && i == ngroups)
+ if (READ_ONCE(sbi->s_mb_stats) && i == ngroups)
atomic64_inc(&sbi->s_bal_cX_failed[cr]);
return 0;
@@ -2541,7 +2541,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
BUG_ON(ac->ac_f_ex.fe_len != ac->ac_g_ex.fe_len);
- if (EXT4_SB(sb)->s_mb_stats)
+ if (READ_ONCE(EXT4_SB(sb)->s_mb_stats))
atomic_inc(&EXT4_SB(sb)->s_bal_2orders);
break;
@@ -2786,7 +2786,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
if (!grp)
return -EFSCORRUPTED;
- if (sbi->s_mb_stats)
+ if (READ_ONCE(sbi->s_mb_stats))
atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
if (should_lock) {
ext4_lock_group(sb, group);
@@ -3097,7 +3097,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
}
}
- if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND) {
+ if (READ_ONCE(sbi->s_mb_stats) && ac->ac_status == AC_STATUS_FOUND) {
atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
if (ac->ac_flags & EXT4_MB_STREAM_ALLOC &&
ac->ac_b_ex.fe_group == ac->ac_g_ex.fe_group)
@@ -3210,7 +3210,7 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
struct ext4_sb_info *sbi = EXT4_SB(sb);
seq_puts(seq, "mballoc:\n");
- if (!sbi->s_mb_stats) {
+ if (!READ_ONCE(sbi->s_mb_stats)) {
seq_puts(seq, "\tmb stats collection turned off.\n");
seq_puts(
seq,
@@ -3787,7 +3787,7 @@ int ext4_mb_init(struct super_block *sb)
sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
sbi->s_mb_min_to_scan = MB_DEFAULT_MIN_TO_SCAN;
- sbi->s_mb_stats = MB_DEFAULT_STATS;
+ WRITE_ONCE(sbi->s_mb_stats, MB_DEFAULT_STATS);
sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
sbi->s_mb_best_avail_max_trim_order = MB_DEFAULT_BEST_AVAIL_TRIM_ORDER;
@@ -3929,7 +3929,7 @@ void ext4_mb_release(struct super_block *sb)
kfree(sbi->s_mb_offsets);
kfree(sbi->s_mb_maxs);
iput(sbi->s_buddy_cache);
- if (sbi->s_mb_stats) {
+ if (READ_ONCE(sbi->s_mb_stats)) {
ext4_msg(sb, KERN_INFO,
"mballoc: %u blocks %u reqs (%u success)",
atomic_read(&sbi->s_bal_allocated),
@@ -4694,7 +4694,7 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
{
struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
- if (sbi->s_mb_stats && ac->ac_g_ex.fe_len >= 1) {
+ if (READ_ONCE(sbi->s_mb_stats) && ac->ac_g_ex.fe_len >= 1) {
atomic_inc(&sbi->s_bal_reqs);
atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index afe12bcc1603..47e06c32c6fb 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -41,6 +41,7 @@ typedef enum {
attr_pointer_atomic,
attr_journal_task,
attr_err_report_sec,
+ attr_mb_stats,
} attr_id_t;
typedef enum {
@@ -241,6 +242,7 @@ EXT4_ATTR_FUNC(session_write_kbytes, 0444);
EXT4_ATTR_FUNC(lifetime_write_kbytes, 0444);
EXT4_ATTR_FUNC(reserved_clusters, 0644);
EXT4_ATTR_FUNC(sra_exceeded_retry_limit, 0444);
+EXT4_ATTR_FUNC(mb_stats, 0644);
EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, inode_readahead,
ext4_sb_info, s_inode_readahead_blks);
@@ -250,7 +252,6 @@ EXT4_ATTR_OFFSET(mb_best_avail_max_trim_order, 0644, mb_order,
ext4_sb_info, s_mb_best_avail_max_trim_order);
EXT4_ATTR_OFFSET(err_report_sec, 0644, err_report_sec, ext4_sb_info, s_err_report_sec);
EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
-EXT4_RW_ATTR_SBI_UI(mb_stats, s_mb_stats);
EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan);
EXT4_RW_ATTR_SBI_UI(mb_min_to_scan, s_mb_min_to_scan);
EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
@@ -451,6 +452,24 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a,
return 0;
}
+static ssize_t mb_stats_show(struct ext4_sb_info *sbi, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", READ_ONCE(sbi->s_mb_stats));
+}
+
+static ssize_t mb_stats_store(struct ext4_sb_info *sbi,
+ const char *buf, size_t len)
+{
+ unsigned int t;
+ int ret;
+
+ ret = kstrtouint(skip_spaces(buf), 0, &t);
+ if (ret)
+ return ret;
+ WRITE_ONCE(sbi->s_mb_stats, t);
+ return len;
+}
+
static ssize_t ext4_attr_show(struct kobject *kobj,
struct attribute *attr, char *buf)
{
@@ -475,6 +494,8 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
return sysfs_emit(buf, "%llu\n",
(unsigned long long)
percpu_counter_sum(&sbi->s_sra_exceeded_retry_limit));
+ case attr_mb_stats:
+ return mb_stats_show(sbi, buf);
case attr_feature:
return sysfs_emit(buf, "supported\n");
case attr_first_error_time:
@@ -559,6 +580,8 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
return inode_readahead_blks_store(sbi, buf, len);
case attr_trigger_test_error:
return trigger_test_error(sbi, buf, len);
+ case attr_mb_stats:
+ return mb_stats_store(sbi, buf, len);
case attr_err_report_sec:
return err_report_sec_store(sbi, buf, len);
default:
--
2.51.0