On 07/25/2016 03:51 AM, Wang Xiaoguang wrote:
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>
---
fs/btrfs/ctree.h | 1 +
fs/btrfs/disk-io.c | 1 +
fs/btrfs/extent-tree.c | 40 ++++++++++++++++++++++++++++++++++------
3 files changed, 36 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..65a1465 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2676,6 +2676,7 @@ int open_ctree(struct super_block *sb,
mutex_init(&fs_info->ordered_operations_mutex);
mutex_init(&fs_info->tree_log_mutex);
mutex_init(&fs_info->chunk_mutex);
+ init_rwsem(&fs_info->bg_delete_sem);
mutex_init(&fs_info->transaction_kthread_mutex);
mutex_init(&fs_info->cleaner_mutex);
mutex_init(&fs_info->volume_mutex);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index df8d756..d1f8638 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 */
@@ -4134,10 +4138,21 @@ again:
if (used + bytes > data_sinfo->total_bytes) {
struct btrfs_trans_handle *trans;
+ spin_unlock(&data_sinfo->lock);
+ /*
+ * We may need to allocate new chunk, so we should block
+ * btrfs_delete_unused_bgs()
+ */
+ if (have_bg_delete_sem == 0) {
+ down_read(&root->fs_info->bg_delete_sem);
+ have_bg_delete_sem = 1;
+ }
+
We could race with somebody else doing an allocation here, so instead do
something like
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; // add a done label at bytes_may_use += bytes
}
Thanks,
Josef
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