[PATCH v4 v4 2/3] ext4: use atomic operations for s_mb_stats accesses

[Baolin Liu <liubaolin12138@163.com>]

From: Baolin Liu <liubaolin@kylinos.cn>

s_mb_stats can be read from mballoc paths while being updated
through sysfs, which can race.
Convert it to atomic_t and use atomic_read()/atomic_set()
for all accesses.

Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
 fs/ext4/ext4.h    |  2 +-
 fs/ext4/mballoc.c | 24 ++++++++++++------------
 fs/ext4/sysfs.c   |  9 ++++++++-
 3 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 293f698b7042..04bccfcb018e 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1624,7 +1624,7 @@ struct ext4_sb_info {
 	unsigned int s_mb_stream_request;
 	unsigned int s_mb_max_to_scan;
 	unsigned int s_mb_min_to_scan;
-	unsigned int s_mb_stats;
+	atomic_t s_mb_stats;
 	unsigned int s_mb_order2_reqs;
 	unsigned int s_mb_group_prealloc;
 	unsigned int s_max_dir_size_kb;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 1e13ef62cb9d..95103fbc1583 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 (atomic_read(&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 (atomic_read(&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 (atomic_read(&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 (atomic_read(&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 (atomic_read(&sbi->s_mb_stats) && i == ngroups)
 		atomic64_inc(&sbi->s_bal_cX_failed[cr]);
 
 	return 0;
@@ -2535,7 +2535,7 @@ 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 (atomic_read(&EXT4_SB(sb)->s_mb_stats))
 			atomic_inc(&EXT4_SB(sb)->s_bal_2orders);
 
 		break;
@@ -2780,7 +2780,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
 
 	if (!grp)
 		return -EFSCORRUPTED;
-	if (sbi->s_mb_stats)
+	if (atomic_read(&sbi->s_mb_stats))
 		atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
 	if (should_lock) {
 		ext4_lock_group(sb, group);
@@ -3091,7 +3091,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 		}
 	}
 
-	if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND) {
+	if (atomic_read(&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)
@@ -3204,7 +3204,7 @@ 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 (!atomic_read(&sbi->s_mb_stats)) {
 		seq_puts(seq, "\tmb stats collection turned off.\n");
 		seq_puts(
 			seq,
@@ -3783,7 +3783,7 @@ 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;
+	atomic_set(&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 (atomic_read(&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 (atomic_read(&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 b87d7bdab06a..0f65ab372dee 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -250,7 +250,7 @@ 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_ATTR_OFFSET(mb_stats, 0644, pointer_atomic, ext4_sb_info, 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);
@@ -493,6 +493,7 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a,
 				       const char *buf, size_t len)
 {
 	int ret;
+	int i;
 	unsigned int t;
 	unsigned long lt;
 	void *ptr = calc_ptr(a, sbi);
@@ -540,6 +541,12 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a,
 			return ret;
 		*((unsigned long *) ptr) = lt;
 		return len;
+	case attr_pointer_atomic:
+		ret = kstrtoint(skip_spaces(buf), 0, &i);
+		if (ret)
+			return ret;
+		atomic_set((atomic_t *)ptr, i);
+		return len;
 	}
 	return 0;
 }
-- 
2.51.0