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Date: Tue, 29 Sep 2015 17:18:15 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Filipe Manana <fdmanana@...e.com>, Josef Bacik <jbacik@...com>, Liu Bo <bo.li.liu@...cle.com>, Chris Mason <clm@...com> Subject: [PATCH 3.14 23/84] Btrfs: check if previous transaction aborted to avoid fs corruption 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Filipe Manana <fdmanana@...e.com> commit 1f9b8c8fbc9a4d029760b16f477b9d15500e3a34 upstream. While we are committing a transaction, it's possible the previous one is still finishing its commit and therefore we wait for it to finish first. However we were not checking if that previous transaction ended up getting aborted after we waited for it to commit, so we ended up committing the current transaction which can lead to fs corruption because the new superblock can point to trees that have had one or more nodes/leafs that were never durably persisted. The following sequence diagram exemplifies how this is possible: CPU 0 CPU 1 transaction N starts (...) btrfs_commit_transaction(N) cur_trans->state = TRANS_STATE_COMMIT_START; (...) cur_trans->state = TRANS_STATE_COMMIT_DOING; (...) cur_trans->state = TRANS_STATE_UNBLOCKED; root->fs_info->running_transaction = NULL; btrfs_start_transaction() --> starts transaction N + 1 btrfs_write_and_wait_transaction(trans, root); --> starts writing all new or COWed ebs created at transaction N creates some new ebs, COWs some existing ebs but doesn't COW or deletes eb X btrfs_commit_transaction(N + 1) (...) cur_trans->state = TRANS_STATE_COMMIT_START; (...) wait_for_commit(root, prev_trans); --> prev_trans == transaction N btrfs_write_and_wait_transaction() continues writing ebs --> fails writing eb X, we abort transaction N and set bit BTRFS_FS_STATE_ERROR on fs_info->fs_state, so no new transactions can start after setting that bit cleanup_transaction() btrfs_cleanup_one_transaction() wakes up task at CPU 1 continues, doesn't abort because cur_trans->aborted (transaction N + 1) is zero, and no checks for bit BTRFS_FS_STATE_ERROR in fs_info->fs_state are made btrfs_write_and_wait_transaction(trans, root); --> succeeds, no errors during writeback write_ctree_super(trans, root, 0); --> succeeds --> we have now a superblock that points us to some root that uses eb X, which was never written to disk In this scenario future attempts to read eb X from disk results in an error message like "parent transid verify failed on X wanted Y found Z". So fix this by aborting the current transaction if after waiting for the previous transaction we verify that it was aborted. Signed-off-by: Filipe Manana <fdmanana@...e.com> Reviewed-by: Josef Bacik <jbacik@...com> Reviewed-by: Liu Bo <bo.li.liu@...cle.com> Signed-off-by: Chris Mason <clm@...com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- fs/btrfs/transaction.c | 3 +++ 1 file changed, 3 insertions(+) --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1710,8 +1710,11 @@ int btrfs_commit_transaction(struct btrf spin_unlock(&root->fs_info->trans_lock); wait_for_commit(root, prev_trans); + ret = prev_trans->aborted; btrfs_put_transaction(prev_trans); + if (ret) + goto cleanup_transaction; } else { spin_unlock(&root->fs_info->trans_lock); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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