On Fri, Dec 01, 2017 at 08:36:19AM -0500, Brian Foster wrote:
> On Thu, Nov 30, 2017 at 09:58:05AM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > In certain cases we need to be able to maintain a buffer lock across a
> > defer_finish call. Since there could be many (large) transactions
> > committed as a result of a defer_finish, we have to hold the buffer
> > across the roll, then immediately rejoin the buffer and mark it dirty in
> > each transaction to keep the log moving forward.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
>
> Seems about right to me. A couple things..
>
> > fs/xfs/libxfs/xfs_defer.c | 37 ++++++++++++++++++++++++++++++++++---
> > fs/xfs/libxfs/xfs_defer.h | 5 ++++-
> > 2 files changed, 38 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> > index 072ebfe..b5b3414 100644
> > --- a/fs/xfs/libxfs/xfs_defer.c
> > +++ b/fs/xfs/libxfs/xfs_defer.c
> > @@ -249,6 +249,10 @@ xfs_defer_trans_roll(
> > for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++)
> > xfs_trans_log_inode(*tp, dop->dop_inodes[i], XFS_ILOG_CORE);
> >
> > + /* Hold the (previously bjoin'd) buffer locked across the roll. */
> > + for (i = 0; i < XFS_DEFER_OPS_NR_BUFS && dop->dop_bufs[i]; i++)
> > + xfs_trans_bhold(*tp, dop->dop_bufs[i]);
> > +
>
> It seems more consistent to dirty the buffer in the tx here and
> bjoin+bhold it in the loop below.
I thought the purpose of calling bhold was to prevent the transaction
commit (in xfs_trans_roll) from unlocking the buffer? Therefore you'd
bhold it before the _roll and then bjoin/dirty the still-locked buffer
afterwards to attach the buffer as a dirty buffer to the new
transaction.
> > trace_xfs_defer_trans_roll((*tp)->t_mountp, dop);
> >
> > /* Roll the transaction. */
> > @@ -264,6 +268,12 @@ xfs_defer_trans_roll(
> > for (i = 0; i < XFS_DEFER_OPS_NR_INODES && dop->dop_inodes[i]; i++)
> > xfs_trans_ijoin(*tp, dop->dop_inodes[i], 0);
> >
> > + /* Rejoin the buffers and dirty them so the log moves forward. */
> > + for (i = 0; i < XFS_DEFER_OPS_NR_BUFS && dop->dop_bufs[i]; i++) {
> > + xfs_trans_bjoin(*tp, dop->dop_bufs[i]);
> > + xfs_trans_dirty_buf(*tp, dop->dop_bufs[i]);
> > + }
> > +
> > return error;
> > }
> >
> > @@ -299,6 +309,29 @@ xfs_defer_ijoin(
> > }
> >
> > /*
> > + * Add this buffer to the deferred op. Each joined buffer is relogged
> > + * each time we roll the transaction.
> > + */
> > +int
> > +xfs_defer_bjoin(
> > + struct xfs_defer_ops *dop,
> > + struct xfs_buf *bp)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < XFS_DEFER_OPS_NR_BUFS; i++) {
> > + if (dop->dop_bufs[i] == bp)
> > + return 0;
> > + else if (dop->dop_bufs[i] == NULL) {
> > + dop->dop_bufs[i] = bp;
> > + return 0;
> > + }
> > + }
> > +
> > + return -EFSCORRUPTED;
>
> I notice that this looks exactly like xfs_defer_join(), but is
> -EFSCORRUPTED the right error here? It probably doesn't matter that much
> given that if we hit this we've already lost, but I wonder if an error
> that more reflects a programming error as opposed to inconsistent fs
> might be more appropriate..? -EINVAL, -EBUSY?
Yeah, I'm not sure what error code applies to "programmer messed up" :)
Perhaps we should add an ASSERT(0) at the bottom of both functions.
--D
> Brian
>
> > +}
> > +
> > +/*
> > * Finish all the pending work. This involves logging intent items for
> > * any work items that wandered in since the last transaction roll (if
> > * one has even happened), rolling the transaction, and finishing the
> > @@ -493,9 +526,7 @@ xfs_defer_init(
> > struct xfs_defer_ops *dop,
> > xfs_fsblock_t *fbp)
> > {
> > - dop->dop_committed = false;
> > - dop->dop_low = false;
> > - memset(&dop->dop_inodes, 0, sizeof(dop->dop_inodes));
> > + memset(dop, 0, sizeof(struct xfs_defer_ops));
> > *fbp = NULLFSBLOCK;
> > INIT_LIST_HEAD(&dop->dop_intake);
> > INIT_LIST_HEAD(&dop->dop_pending);
> > diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
> > index d4f046d..045beac 100644
> > --- a/fs/xfs/libxfs/xfs_defer.h
> > +++ b/fs/xfs/libxfs/xfs_defer.h
> > @@ -59,6 +59,7 @@ enum xfs_defer_ops_type {
> > };
> >
> > #define XFS_DEFER_OPS_NR_INODES 2 /* join up to two inodes */
> > +#define XFS_DEFER_OPS_NR_BUFS 2 /* join up to two buffers */
> >
> > struct xfs_defer_ops {
> > bool dop_committed; /* did any trans commit? */
> > @@ -66,8 +67,9 @@ struct xfs_defer_ops {
> > struct list_head dop_intake; /* unlogged pending work */
> > struct list_head dop_pending; /* logged pending work */
> >
> > - /* relog these inodes with each roll */
> > + /* relog these with each roll */
> > struct xfs_inode *dop_inodes[XFS_DEFER_OPS_NR_INODES];
> > + struct xfs_buf *dop_bufs[XFS_DEFER_OPS_NR_BUFS];
> > };
> >
> > void xfs_defer_add(struct xfs_defer_ops *dop, enum xfs_defer_ops_type type,
> > @@ -77,6 +79,7 @@ void xfs_defer_cancel(struct xfs_defer_ops *dop);
> > void xfs_defer_init(struct xfs_defer_ops *dop, xfs_fsblock_t *fbp);
> > bool xfs_defer_has_unfinished_work(struct xfs_defer_ops *dop);
> > int xfs_defer_ijoin(struct xfs_defer_ops *dop, struct xfs_inode *ip);
> > +int xfs_defer_bjoin(struct xfs_defer_ops *dop, struct xfs_buf *bp);
> >
> > /* Description of a deferred type. */
> > struct xfs_defer_op_type {
> > --
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