[PATCH v2] ext4: cond_resched in work-heavy group loops

[Khazhismel Kumykov]

These functions may take a long time looping over many groups, which
may cause issues for non-preempt kernels.
ext4_mb_init_backend()
ext4_setup_system_zone()
ext4_mb_release()

Signed-off-by: Khazhismel Kumykov <kha...@google.com>
---
v2: 
 - a few other places that in testing showed to be slow

 fs/ext4/block_validity.c | 1 +
 fs/ext4/mballoc.c        | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index 913061c0de1b..16134469ea3c 100644
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -155,6 +155,7 @@ int ext4_setup_system_zone(struct super_block *sb)
                return 0;
 
        for (i=0; i < ngroups; i++) {
+               cond_resched();
                if (ext4_bg_has_super(sb, i) &&
                    ((i < 5) || ((i % flex_size) == 0)))
                        add_system_zone(sbi, ext4_group_first_block_no(sb, i),
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8ef5f12bbee2..99ba720dbb7a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2490,6 +2490,7 @@ static int ext4_mb_init_backend(struct super_block *sb)
        sbi->s_buddy_cache->i_ino = EXT4_BAD_INO;
        EXT4_I(sbi->s_buddy_cache)->i_disksize = 0;
        for (i = 0; i < ngroups; i++) {
+               cond_resched();
                desc = ext4_get_group_desc(sb, i, NULL);
                if (desc == NULL) {
                        ext4_msg(sb, KERN_ERR, "can't read descriptor %u", i);
@@ -2705,6 +2706,7 @@ int ext4_mb_release(struct super_block *sb)
 
        if (sbi->s_group_info) {
                for (i = 0; i < ngroups; i++) {
+                       cond_resched();
                        grinfo = ext4_get_group_info(sb, i);
 #ifdef DOUBLE_CHECK
                        kfree(grinfo->bb_bitmap);
-- 
2.21.0.593.g511ec345e18-goog