Hello,
I know, the discussion on how to fix the problem best is still on-going,
but I wanted to add that I tried v3 of the patch against btrfs-next on
my machine. Without the patch, I was able to reproduce the problem
within a few minutes; after applying it, I wasn't able to trigger it for
50 minutes now.
I can't tell whether the problem would reoccur when running my little
test for another week or so, but I can tell that my machine did not
catch fire either. So it seems like you're on the right track. :)
I can also try another version of the patch when it becomes available.
Thanks,
Sebastian
On 02.12.2013 18:33, Wang Shilong wrote:
From: Wang Shilong <wangsl.fnst@xxxxxxxxxxxxxx>
We came a race condition when scrubbing superblocks, the story is:
In commiting transaction, we will update last_trans_commited after
writting superblocks. if a scrub start after writting superblocks
and before last_trans_commited, generation mismatch happens!
We fix it by protecting writting superblock and updating last_trans_commited
with tree_log_mutex.
Reported-by: Sebastian Ochmann <ochmann@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wang Shilong <wangsl.fnst@xxxxxxxxxxxxxx>
---
Changelog:
v2->v3:move tree_log_mutex out of device_list_mutex.
v1->v2: use right way to fix the problem.
---
fs/btrfs/scrub.c | 11 +++++++----
fs/btrfs/transaction.c | 13 ++++++++++---
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 561e2f1..a9ed102 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2887,6 +2887,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
}
+ mutex_lock(&fs_info->tree_log_mutex);
mutex_lock(&fs_info->fs_devices->device_list_mutex);
dev = btrfs_find_device(fs_info, devid, NULL, NULL);
if (!dev || (dev->missing && !is_dev_replace)) {
@@ -2932,14 +2933,16 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
atomic_inc(&fs_info->scrubs_running);
mutex_unlock(&fs_info->scrub_lock);
+ /*
+ * holding tree_log_mutex we can avoid generation mismatch while
+ * scrubbing superblocks, see comments in commiting transaction
+ * when updating last_trans_commited.
+ */
if (!is_dev_replace) {
- /*
- * by holding device list mutex, we can
- * kick off writing super in log tree sync.
- */
ret = scrub_supers(sctx, dev);
}
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+ mutex_unlock(&fs_info->tree_log_mutex);
if (!ret)
ret = scrub_enumerate_chunks(sctx, dev, start, end,
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c6a872a..052eb22 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1898,15 +1898,22 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
goto cleanup_transaction;
}
+ btrfs_finish_extent_commit(trans, root);
+
+ /*
+ * we must gurantee last_trans_commited update is protected by
+ * tree_log_mutex with write_ctree_super together, otherwise,
+ * scubbing super will come in before updating last_trans_commited
+ * and we will get generation mismatch when scrubbing superblocks.
+ */
+ root->fs_info->last_trans_committed = cur_trans->transid;
+
/*
* the super is written, we can safely allow the tree-loggers
* to go about their business
*/
mutex_unlock(&root->fs_info->tree_log_mutex);
- btrfs_finish_extent_commit(trans, root);
-
- root->fs_info->last_trans_committed = cur_trans->transid;
/*
* We needn't acquire the lock here because there is no other task
* which can change it.
--
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