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Btrfs: fix race in WAIT_SYNC ioctl 

We check whether transid is already committed via last_trans_committed and
then search through trans_list for pending transactions.  If
last_trans_committed is updated by btrfs_commit_transaction after we check
it (there is no locking), we will fail to find the committed transaction
and return EINVAL to the caller.  This has been observed occasionally by
ceph-osd (which uses this ioctl heavily).

Fix by rechecking whether the provided transid <= last_trans_committed
after the search fails, and if so return 0.

Signed-off-by: Sage Weil <sage@redhat.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Sage Weil 2014-09-26 08:30:06 -07:00 committed by Chris Mason
parent 656f30dba7
commit 42383020be
1 changed files with 9 additions and 3 deletions
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12
fs/btrfs/transaction.c
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@ -609,7 +609,6 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
if (transid <= root->fs_info->last_trans_committed)
goto out;
ret = -EINVAL;
/* find specified transaction */
spin_lock(&root->fs_info->trans_lock);
list_for_each_entry(t, &root->fs_info->trans_list, list) {
@ -625,9 +624,16 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
}
}
spin_unlock(&root->fs_info->trans_lock);
/* The specified transaction doesn't exist */
if (!cur_trans)
/*
* The specified transaction doesn't exist, or we
* raced with btrfs_commit_transaction
*/
if (!cur_trans) {
if (transid > root->fs_info->last_trans_committed)
ret = -EINVAL;
goto out;
}
} else {
/* find newest transaction that is committing | committed */
spin_lock(&root->fs_info->trans_lock);