cleaner_kthread() may run at any time, in which it'll call btrfs_delete_unused_bgs()
to delete unused block groups. Because this work is asynchronous, it may also result
in false ENOSPC error. Please see below race window:
CPU1 | CPU2
|
|-> btrfs_alloc_data_chunk_ondemand() |-> cleaner_kthread()
|-> do_chunk_alloc() | |
| assume it returns ENOSPC, which means | |
| btrfs_space_info is full and have free| |
| space to satisfy data request. | |
| | |- > btrfs_delete_unused_bgs()
| | | it will decrease btrfs_space_info
| | | total_bytes and make
| | | btrfs_space_info is not full.
| | |
In this case, we may get ENOSPC error, but btrfs_space_info is not full.
To fix this issue, in btrfs_alloc_data_chunk_ondemand(), if we need to call
do_chunk_alloc() to allocating new chunk, we should block btrfs_delete_unused_bgs().
So here we introduce a new struct rw_semaphore bg_delete_sem to do this job.
Signed-off-by: Wang Xiaoguang <wangxg.fnst@xxxxxxxxxxxxxx>
---
v3: improve one code logic suggested by Josef, thanks.
---
fs/btrfs/ctree.h | 1 +
fs/btrfs/disk-io.c | 1 +
fs/btrfs/extent-tree.c | 44 ++++++++++++++++++++++++++++++++++++++------
3 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 7eb2913..bf0751d 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -800,6 +800,7 @@ struct btrfs_fs_info {
struct mutex cleaner_mutex;
struct mutex chunk_mutex;
struct mutex volume_mutex;
+ struct rw_semaphore bg_delete_sem;
/*
* this is taken to make sure we don't set block groups ro after
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 60ce119..f8609fd 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2683,6 +2683,7 @@ int open_ctree(struct super_block *sb,
init_rwsem(&fs_info->commit_root_sem);
init_rwsem(&fs_info->cleanup_work_sem);
init_rwsem(&fs_info->subvol_sem);
+ init_rwsem(&fs_info->bg_delete_sem);
sema_init(&fs_info->uuid_tree_rescan_sem, 1);
btrfs_init_dev_replace_locks(fs_info);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index df8d756..50b440e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4111,6 +4111,7 @@ int btrfs_alloc_data_chunk_ondemand(struct inode *inode, u64 bytes)
int ret = 0;
int need_commit = 2;
int have_pinned_space;
+ int have_bg_delete_sem = 0;
/* make sure bytes are sectorsize aligned */
bytes = ALIGN(bytes, root->sectorsize);
@@ -4121,8 +4122,11 @@ int btrfs_alloc_data_chunk_ondemand(struct inode *inode, u64 bytes)
}
data_sinfo = fs_info->data_sinfo;
- if (!data_sinfo)
+ if (!data_sinfo) {
+ down_read(&root->fs_info->bg_delete_sem);
+ have_bg_delete_sem = 1;
goto alloc;
+ }
again:
/* make sure we have enough space to handle the data first */
@@ -4135,6 +4139,19 @@ again:
struct btrfs_trans_handle *trans;
/*
+ * We may need to allocate new chunk, so we should block
+ * btrfs_delete_unused_bgs()
+ */
+ if (!have_bg_delete_sem) {
+ spin_unlock(&data_sinfo->lock);
+ down_read(&root->fs_info->bg_delete_sem);
+ have_bg_delete_sem = 1;
+ spin_lock(&data_sinfo->lock);
+ if (used + bytes <= data_sinfo->total_bytes)
+ goto done;
+ }
+
+ /*
* if we don't have enough free bytes in this space then we need
* to alloc a new chunk.
*/
@@ -4156,17 +4173,20 @@ alloc:
* the fs.
*/
trans = btrfs_join_transaction(root);
- if (IS_ERR(trans))
+ if (IS_ERR(trans)) {
+ up_read(&root->fs_info->bg_delete_sem);
return PTR_ERR(trans);
+ }
ret = do_chunk_alloc(trans, root->fs_info->extent_root,
alloc_target,
CHUNK_ALLOC_NO_FORCE);
btrfs_end_transaction(trans, root);
if (ret < 0) {
- if (ret != -ENOSPC)
+ if (ret != -ENOSPC) {
+ up_read(&root->fs_info->bg_delete_sem);
return ret;
- else {
+ } else {
have_pinned_space = 1;
goto commit_trans;
}
@@ -4200,15 +4220,19 @@ commit_trans:
}
trans = btrfs_join_transaction(root);
- if (IS_ERR(trans))
+ if (IS_ERR(trans)) {
+ up_read(&root->fs_info->bg_delete_sem);
return PTR_ERR(trans);
+ }
if (have_pinned_space >= 0 ||
test_bit(BTRFS_TRANS_HAVE_FREE_BGS,
&trans->transaction->flags) ||
need_commit > 0) {
ret = btrfs_commit_transaction(trans, root);
- if (ret)
+ if (ret) {
+ up_read(&root->fs_info->bg_delete_sem);
return ret;
+ }
/*
* The cleaner kthread might still be doing iput
* operations. Wait for it to finish so that
@@ -4225,13 +4249,19 @@ commit_trans:
trace_btrfs_space_reservation(root->fs_info,
"space_info:enospc",
data_sinfo->flags, bytes, 1);
+ up_read(&root->fs_info->bg_delete_sem);
return -ENOSPC;
}
+
+done:
data_sinfo->bytes_may_use += bytes;
trace_btrfs_space_reservation(root->fs_info, "space_info",
data_sinfo->flags, bytes, 1);
spin_unlock(&data_sinfo->lock);
+ if (have_bg_delete_sem)
+ up_read(&root->fs_info->bg_delete_sem);
+
return ret;
}
@@ -10594,6 +10624,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
spin_unlock(&fs_info->unused_bgs_lock);
mutex_lock(&fs_info->delete_unused_bgs_mutex);
+ down_write(&root->fs_info->bg_delete_sem);
/* Don't want to race with allocators so take the groups_sem */
down_write(&space_info->groups_sem);
@@ -10721,6 +10752,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
end_trans:
btrfs_end_transaction(trans, root);
next:
+ up_write(&root->fs_info->bg_delete_sem);
mutex_unlock(&fs_info->delete_unused_bgs_mutex);
btrfs_put_block_group(block_group);
spin_lock(&fs_info->unused_bgs_lock);
--
2.9.0
--
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