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>
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@ -609,7 +609,6 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
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if (transid <= root->fs_info->last_trans_committed)
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goto out;
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ret = -EINVAL;
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/* find specified transaction */
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spin_lock(&root->fs_info->trans_lock);
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list_for_each_entry(t, &root->fs_info->trans_list, list) {
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@ -625,9 +624,16 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
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}
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}
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spin_unlock(&root->fs_info->trans_lock);
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/* The specified transaction doesn't exist */
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if (!cur_trans)
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/*
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* The specified transaction doesn't exist, or we
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* raced with btrfs_commit_transaction
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*/
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if (!cur_trans) {
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if (transid > root->fs_info->last_trans_committed)
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ret = -EINVAL;
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goto out;
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}
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} else {
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/* find newest transaction that is committing | committed */
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spin_lock(&root->fs_info->trans_lock);
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