ext4_mb_good_group() definition was changed some time back
and now it even initializes the buddy cache (via ext4_mb_init_group()),
if in case the EXT4_MB_GRP_NEED_INIT() is true for a group.
Note that ext4_mb_init_group() could sleep and so should not be called
under a spinlock held.
This is fine as of now because ext4_mb_good_group() is called before
loading the buddy bitmap without ext4_lock_group() held
and again called after loading the bitmap, only this time with
ext4_lock_group() held.
But still this whole thing is confusing.
So this patch refactors out ext4_mb_good_group_nolock() which should be
called when without holding ext4_lock_group().
Also in further patches we hold the spinlock (ext4_lock_group()) while
doing any calculations which involves grp->bb_free or grp->bb_fragments.
Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
---
fs/ext4/mballoc.c | 80 ++++++++++++++++++++++++++++++-----------------
1 file changed, 52 insertions(+), 28 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 33a69424942c..da11a4a738bd 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2066,15 +2066,16 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
}
/*
- * This is now called BEFORE we load the buddy bitmap.
+ * This is also called BEFORE we load the buddy bitmap.
* Returns either 1 or 0 indicating that the group is either suitable
- * for the allocation or not. In addition it can also return negative
- * error code when something goes wrong.
+ * for the allocation or not. This should be called with ext4_lock_group()
+ * held to protect grp->bb_free from getting changed due to another
+ * allocation/discard is happening in parallel.
*/
-static int ext4_mb_good_group(struct ext4_allocation_context *ac,
+static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
ext4_group_t group, int cr)
{
- unsigned free, fragments;
+ ext4_grpblk_t free, fragments;
int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
@@ -2082,23 +2083,16 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
free = grp->bb_free;
if (free == 0)
- return 0;
+ return false;
if (cr <= 2 && free < ac->ac_g_ex.fe_len)
- return 0;
+ return false;
if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
- return 0;
-
- /* We only do this if the grp has never been initialized */
- if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
- int ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
- if (ret)
- return ret;
- }
+ return false;
fragments = grp->bb_fragments;
if (fragments == 0)
- return 0;
+ return false;
switch (cr) {
case 0:
@@ -2108,31 +2102,63 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
(flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
((group % flex_size) == 0))
- return 0;
+ return false;
if ((ac->ac_2order > ac->ac_sb->s_blocksize_bits+1) ||
(free / fragments) >= ac->ac_g_ex.fe_len)
- return 1;
+ return true;
if (grp->bb_largest_free_order < ac->ac_2order)
- return 0;
+ return false;
- return 1;
+ return true;
case 1:
if ((free / fragments) >= ac->ac_g_ex.fe_len)
- return 1;
+ return true;
break;
case 2:
if (free >= ac->ac_g_ex.fe_len)
- return 1;
+ return true;
break;
case 3:
- return 1;
+ return true;
default:
BUG();
}
- return 0;
+ return false;
+}
+
+/*
+ * This could return negative error code if something goes wrong
+ * during ext4_mb_init_group(). This should not be called with
+ * ext4_lock_group() held.
+ */
+static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
+ ext4_group_t group, int cr)
+{
+ struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
+ ext4_grpblk_t free;
+ int ret = 0;
+
+ free = grp->bb_free;
+ if (free == 0)
+ goto out;
+ if (cr <= 2 && free < ac->ac_g_ex.fe_len)
+ goto out;
+ if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
+ goto out;
+
+ /* We only do this if the grp has never been initialized */
+ if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
+ ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
+ if (ret)
+ return ret;
+ }
+
+ ret = ext4_mb_good_group(ac, group, cr);
+out:
+ return ret;
}
static noinline_for_stack int
@@ -2220,7 +2246,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
group = 0;
/* This now checks without needing the buddy page */
- ret = ext4_mb_good_group(ac, group, cr);
+ ret = ext4_mb_good_group_nolock(ac, group, cr);
if (ret <= 0) {
if (!first_err)
first_err = ret;
@@ -2238,11 +2264,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
* block group
*/
ret = ext4_mb_good_group(ac, group, cr);
- if (ret <= 0) {
+ if (ret == 0) {
ext4_unlock_group(sb, group);
ext4_mb_unload_buddy(&e4b);
- if (!first_err)
- first_err = ret;
continue;
}
--
2.21.0
