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xfs: release new dquot buffer on defer_finish error 

In commit efa092f3d4 "[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
310a75a3c6 ("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 <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
This commit is contained in:
Darrick J. Wong 2018-05-04 15:30:19 -07:00
parent 84ca484ecf
commit 7b6b50f55c
1 changed files with 29 additions and 21 deletions
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50
fs/xfs/xfs_dquot.c
View File

@ -362,32 +362,40 @@ 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 and joined to the transaction. The caller
* is responsible for unlocking any buffer passed back, either
* manually or by committing the transaction.
*/
xfs_trans_bhold(tp, bp);
error = xfs_defer_finish(tpp, &dfops);
if (error)
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;
/* Transaction was committed? */
if (*tpp != tp) {
tp = *tpp;
xfs_trans_bjoin(tp, bp);
} else {
xfs_trans_bhold_release(tp, bp);
}
error = xfs_defer_finish(tpp, &dfops);
if (error) {
xfs_buf_relse(bp);
goto error1;
}
xfs_trans_bhold_release(*tpp, bp);
*O_bpp = bp;
return 0;