From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2130.oracle.com ([156.151.31.86]:51612 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751075AbeECRyI (ORCPT ); Thu, 3 May 2018 13:54:08 -0400 Date: Thu, 3 May 2018 10:53:43 -0700 From: "Darrick J. Wong" Subject: [PATCH 0.1/13] xfs: release new dquot buffer on defer_finish error Message-ID: <20180503175343.GF4127@magnolia> References: <152506698177.21553.13500862866416804148.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152506698177.21553.13500862866416804148.stgit@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: linux-xfs@vger.kernel.org, bfoster@redhat.com, hch@lst.de From: Darrick J. Wong In commit efa092f3d4c6 "[XFS] Fixes a bug in the quota code when allocating a new dquot record", we allocate a new dquot block, grab a buffer to initialize it, and return the locked initialized dquot buffer to the caller for further in-core dquot initialization. Unfortunately, if the _bmap_finish errored out, _qm_dqalloc would also error out without bothering to free the (locked) buffer. Leaking a locked buffer caused hangs in generic/388 when quotas are enabled. Furthermore, the _bmap_finish -> _defer_finish conversion in 310a75a3c6c747 ("xfs: change xfs_bmap_{finish,cancel,init,free} -> xfs_defer_*") failed to observe that the buffer was held going into _defer_finish and therefore failed to notice that the buffer lock is /not/ maintained afterwards. Now that we can bjoin a buffer to a defer_ops, use this mechanism to ensure that the buffer stays locked across the _defer_finish. Release the holds and locks on the buffer as appropriate if we have to error out. There is a subtlety here for the caller in that the buffer emerges locked and held to the transaction, so if the _trans_commit fails we have to release the buffer explicitly. This fixes the unmount hang in generic/388 when quotas are enabled. Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_dquot.c | 48 +++++++++++++++++++++++++++--------------------- 1 file changed, 27 insertions(+), 21 deletions(-) diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index a7daef9e16bf..4c39d8632230 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -362,33 +362,39 @@ xfs_qm_dqalloc( dqp->dq_flags & XFS_DQ_ALLTYPES, bp); /* - * xfs_defer_finish() may commit the current transaction and - * start a second transaction if the freelist is not empty. + * Hold the buffer and join it to the dfops so that we'll still own + * the buffer when we return to the caller. The buffer disposal on + * error must be paid attention to very carefully, as it has been + * broken since commit efa092f3d4c6 "[XFS] Fixes a bug in the quota + * code when allocating a new dquot record" in 2005, and the later + * conversion to xfs_defer_ops in commit 310a75a3c6c747 failed to keep + * the buffer locked across the _defer_finish call. We can now do + * this correctly with xfs_defer_bjoin. * - * Since we still want to modify this buffer, we need to - * ensure that the buffer is not released on commit of - * the first transaction and ensure the buffer is added to the - * second transaction. + * Above, we allocated a disk block for the dquot information and + * used get_buf to initialize the dquot. If the _defer_bjoin fails, + * the buffer is still locked to *tpp, so we must _bhold_release and + * then _trans_brelse the buffer. If the _defer_finish fails, the old + * transaction is gone but the new buffer is not joined or held to any + * transaction, so we must _buf_relse it. * - * If there is only one transaction then don't stop the buffer - * from being released when it commits later on. + * If everything succeeds, the caller of this function is returned a + * buffer that is locked, held, and joined to the transaction. If the + * transaction commit fails (in the caller) the caller must unlock the + * buffer manually. */ - - xfs_trans_bhold(tp, bp); - + xfs_trans_bhold(*tpp, bp); + error = xfs_defer_bjoin(&dfops, bp); + if (error) { + xfs_trans_bhold_release(*tpp, bp); + xfs_trans_brelse(*tpp, bp); + goto error1; + } error = xfs_defer_finish(tpp, &dfops); - if (error) + if (error) { + xfs_buf_relse(bp); goto error1; - - /* Transaction was committed? */ - if (*tpp != tp) { - tp = *tpp; - xfs_trans_bjoin(tp, bp); - } else { - xfs_trans_bhold_release(tp, bp); } - - *O_bpp = bp; return 0; error1: