On Fri, Apr 03, 2020 at 03:12:27PM -0700, Allison Collins wrote:
> This patch modifies the attr remove routines to be delay ready. This
> means they no longer roll or commit transactions, but instead return
> -EAGAIN to have the calling routine roll and refresh the transaction. In
> this series, xfs_attr_remove_args has become xfs_attr_remove_iter, which
> uses a sort of state machine like switch to keep track of where it was
> when EAGAIN was returned. xfs_attr_node_removename has also been
> modified to use the switch, and a new version of xfs_attr_remove_args
> consists of a simple loop to refresh the transaction until the operation
> is completed.
>
> Calls to xfs_attr_rmtval_remove are replaced with the delay ready
> counter parts: xfs_attr_rmtval_invalidate (appearing in the setup
> helper) and then __xfs_attr_rmtval_remove. We will rename
> __xfs_attr_rmtval_remove back to xfs_attr_rmtval_remove when we are
> done.
>
> This patch also adds a new struct xfs_delattr_context, which we will use
> to keep track of the current state of an attribute operation. The new
> xfs_delattr_state enum is used to track various operations that are in
> progress so that we know not to repeat them, and resume where we left
> off before EAGAIN was returned to cycle out the transaction. Other
> members take the place of local variables that need to retain their
> values across multiple function recalls.
>
> Below is a state machine diagram for attr remove operations. The
> XFS_DAS_* states indicate places where the function would return
> -EAGAIN, and then immediately resume from after being recalled by the
> calling function. States marked as a "subroutine state" indicate that
> they belong to a subroutine, and so the calling function needs to pass
> them back to that subroutine to allow it to finish where it left off.
> But they otherwise do not have a role in the calling function other than
> just passing through.
>
> xfs_attr_remove_iter()
> XFS_DAS_RM_SHRINK ─┐
> (subroutine state) │
> │
> XFS_DAS_RMTVAL_REMOVE ─┤
> (subroutine state) │
> └─>xfs_attr_node_removename()
> │
> v
> need to remove
> ┌─n── rmt blocks?
> │ │
> │ y
> │ │
> │ v
> │ ┌─>XFS_DAS_RMTVAL_REMOVE
> │ │ │
> │ │ v
> │ └──y── more blks
> │ to remove?
> │ │
> │ n
> │ │
> │ v
> │ need to
> └─────> shrink tree? ─n─┐
> │ │
> y │
> │ │
> v │
> XFS_DAS_RM_SHRINK │
> │ │
> v │
> done <─────┘
>
> Signed-off-by: Allison Collins <allison.henderson@xxxxxxxxxx>
> ---
All in all this is starting to look much more simple to me, at least in
the remove path. ;P There's only a few states and the markers that are
introduced are fairly straightforward, etc. Comments to follow..
> fs/xfs/libxfs/xfs_attr.c | 168 ++++++++++++++++++++++++++++++++++++-----------
> fs/xfs/libxfs/xfs_attr.h | 38 +++++++++++
> 2 files changed, 168 insertions(+), 38 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index d735570..f700976 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -45,7 +45,7 @@ STATIC int xfs_attr_shortform_addname(xfs_da_args_t *args);
> */
> STATIC int xfs_attr_leaf_get(xfs_da_args_t *args);
> STATIC int xfs_attr_leaf_addname(xfs_da_args_t *args);
> -STATIC int xfs_attr_leaf_removename(xfs_da_args_t *args);
> +STATIC int xfs_attr_leaf_removename(struct xfs_delattr_context *dac);
> STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
>
> /*
> @@ -53,12 +53,21 @@ STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
> */
> STATIC int xfs_attr_node_get(xfs_da_args_t *args);
> STATIC int xfs_attr_node_addname(xfs_da_args_t *args);
> -STATIC int xfs_attr_node_removename(xfs_da_args_t *args);
> +STATIC int xfs_attr_node_removename(struct xfs_delattr_context *dac);
> STATIC int xfs_attr_node_hasname(xfs_da_args_t *args,
> struct xfs_da_state **state);
> STATIC int xfs_attr_fillstate(xfs_da_state_t *state);
> STATIC int xfs_attr_refillstate(xfs_da_state_t *state);
>
> +STATIC void
> +xfs_delattr_context_init(
> + struct xfs_delattr_context *dac,
> + struct xfs_da_args *args)
> +{
> + memset(dac, 0, sizeof(struct xfs_delattr_context));
> + dac->da_args = args;
> +}
> +
> int
> xfs_inode_hasattr(
> struct xfs_inode *ip)
> @@ -356,20 +365,66 @@ xfs_has_attr(
> */
> int
> xfs_attr_remove_args(
> - struct xfs_da_args *args)
> + struct xfs_da_args *args)
> {
> + int error = 0;
> + struct xfs_delattr_context dac;
> +
> + xfs_delattr_context_init(&dac, args);
> +
> + do {
> + error = xfs_attr_remove_iter(&dac);
> + if (error != -EAGAIN)
> + break;
> +
> + if (dac.flags & XFS_DAC_DEFER_FINISH) {
> + dac.flags &= ~XFS_DAC_DEFER_FINISH;
> + error = xfs_defer_finish(&args->trans);
> + if (error)
> + break;
> + }
> +
> + error = xfs_trans_roll_inode(&args->trans, args->dp);
> + if (error)
> + break;
> + } while (true);
> +
> + return error;
> +}
> +
> +/*
> + * Remove the attribute specified in @args.
> + *
> + * This function may return -EAGAIN to signal that the transaction needs to be
> + * rolled. Callers should continue calling this function until they receive a
> + * return value other than -EAGAIN.
> + */
> +int
> +xfs_attr_remove_iter(
> + struct xfs_delattr_context *dac)
> +{
> + struct xfs_da_args *args = dac->da_args;
> struct xfs_inode *dp = args->dp;
> int error;
>
> + /* State machine switch */
> + switch (dac->dela_state) {
> + case XFS_DAS_RM_SHRINK:
> + case XFS_DAS_RMTVAL_REMOVE:
> + return xfs_attr_node_removename(dac);
> + default:
> + break;
> + }
> +
Hmm.. so we're duplicating the call instead of using labels..? I'm
wondering if this can be elegantly combined with the if/else branches
below, particularly since node format is the only situation that seems
to require a roll here.
> if (!xfs_inode_hasattr(dp)) {
> error = -ENOATTR;
> } else if (dp->i_d.di_aformat == XFS_DINODE_FMT_LOCAL) {
> ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
> error = xfs_attr_shortform_remove(args);
> } else if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> - error = xfs_attr_leaf_removename(args);
> + error = xfs_attr_leaf_removename(dac);
> } else {
> - error = xfs_attr_node_removename(args);
> + error = xfs_attr_node_removename(dac);
> }
>
> return error;
> @@ -794,11 +849,12 @@ xfs_attr_leaf_hasname(
> */
> STATIC int
> xfs_attr_leaf_removename(
> - struct xfs_da_args *args)
> + struct xfs_delattr_context *dac)
> {
> - struct xfs_inode *dp;
> - struct xfs_buf *bp;
> - int error, forkoff;
> + struct xfs_da_args *args = dac->da_args;
> + struct xfs_inode *dp;
> + struct xfs_buf *bp;
> + int error, forkoff;
>
> trace_xfs_attr_leaf_removename(args);
>
> @@ -825,9 +881,8 @@ xfs_attr_leaf_removename(
> /* bp is gone due to xfs_da_shrink_inode */
> if (error)
> return error;
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - return error;
> +
> + dac->flags |= XFS_DAC_DEFER_FINISH;
There's no -EAGAIN return here, is this an exit path for the remove?
> }
> return 0;
> }
> @@ -1128,12 +1183,13 @@ xfs_attr_node_addname(
> */
> STATIC int
> xfs_attr_node_shrink(
> - struct xfs_da_args *args,
> - struct xfs_da_state *state)
> + struct xfs_delattr_context *dac,
> + struct xfs_da_state *state)
> {
> - struct xfs_inode *dp = args->dp;
> - int error, forkoff;
> - struct xfs_buf *bp;
> + struct xfs_da_args *args = dac->da_args;
> + struct xfs_inode *dp = args->dp;
> + int error, forkoff;
> + struct xfs_buf *bp;
>
> /*
> * Have to get rid of the copy of this dabuf in the state.
> @@ -1153,9 +1209,7 @@ xfs_attr_node_shrink(
> if (error)
> return error;
>
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - return error;
> + dac->flags |= XFS_DAC_DEFER_FINISH;
Same question here.
> } else
> xfs_trans_brelse(args->trans, bp);
>
> @@ -1194,13 +1248,15 @@ xfs_attr_leaf_mark_incomplete(
>
> /*
> * Initial setup for xfs_attr_node_removename. Make sure the attr is there and
> - * the blocks are valid. Any remote blocks will be marked incomplete.
> + * the blocks are valid. Any remote blocks will be marked incomplete and
> + * invalidated.
> */
> STATIC
> int xfs_attr_node_removename_setup(
> - struct xfs_da_args *args,
> - struct xfs_da_state **state)
> + struct xfs_delattr_context *dac,
> + struct xfs_da_state **state)
> {
> + struct xfs_da_args *args = dac->da_args;
> int error;
> struct xfs_da_state_blk *blk;
>
> @@ -1212,10 +1268,21 @@ int xfs_attr_node_removename_setup(
> ASSERT(blk->bp != NULL);
> ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
>
> + /*
> + * Store blk and state in the context incase we need to cycle out the
> + * transaction
> + */
> + dac->blk = blk;
> + dac->da_state = *state;
> +
> if (args->rmtblkno > 0) {
> error = xfs_attr_leaf_mark_incomplete(args, *state);
> if (error)
> return error;
> +
> + error = xfs_attr_rmtval_invalidate(args);
> + if (error)
> + return error;
Seems like this moves code, which should probably happen in a separate
patch.
> }
>
> return 0;
> @@ -1228,7 +1295,10 @@ xfs_attr_node_removename_rmt (
> {
> int error = 0;
>
> - error = xfs_attr_rmtval_remove(args);
> + /*
> + * May return -EAGAIN to request that the caller recall this function
> + */
> + error = __xfs_attr_rmtval_remove(args);
> if (error)
> return error;
>
> @@ -1249,19 +1319,37 @@ xfs_attr_node_removename_rmt (
> * This will involve walking down the Btree, and may involve joining
> * leaf nodes and even joining intermediate nodes up to and including
> * the root node (a special case of an intermediate node).
> + *
> + * This routine is meant to function as either an inline or delayed operation,
> + * and may return -EAGAIN when the transaction needs to be rolled. Calling
> + * functions will need to handle this, and recall the function until a
> + * successful error code is returned.
> */
> STATIC int
> xfs_attr_node_removename(
> - struct xfs_da_args *args)
> + struct xfs_delattr_context *dac)
> {
> + struct xfs_da_args *args = dac->da_args;
> struct xfs_da_state *state;
> struct xfs_da_state_blk *blk;
> int retval, error;
> struct xfs_inode *dp = args->dp;
>
> trace_xfs_attr_node_removename(args);
> + state = dac->da_state;
> + blk = dac->blk;
> +
> + /* State machine switch */
> + switch (dac->dela_state) {
> + case XFS_DAS_RMTVAL_REMOVE:
> + goto das_rmtval_remove;
> + case XFS_DAS_RM_SHRINK:
> + goto das_rm_shrink;
> + default:
> + break;
> + }
>
> - error = xfs_attr_node_removename_setup(args, &state);
> + error = xfs_attr_node_removename_setup(dac, &state);
> if (error)
> goto out;
>
> @@ -1270,10 +1358,16 @@ xfs_attr_node_removename(
> * This is done before we remove the attribute so that we don't
> * overflow the maximum size of a transaction and/or hit a deadlock.
> */
> +
> +das_rmtval_remove:
> +
I wonder if we need this label just to protect the setup. Perhaps if we
had something like:
/* set up the remove only once... */
if (dela_state == 0)
error = xfs_attr_node_removename_setup(...);
... we could reduce another state.
We could also accomplish the same thing with an explicit state to
indicate the setup already occurred or a new dac flag, though I'm not
sure a flag is appropriate if it would only be used here.
Brian
> if (args->rmtblkno > 0) {
> error = xfs_attr_node_removename_rmt(args, state);
> - if (error)
> - goto out;
> + if (error) {
> + if (error == -EAGAIN)
> + dac->dela_state = XFS_DAS_RMTVAL_REMOVE;
> + return error;
> + }
> }
>
> /*
> @@ -1291,22 +1385,20 @@ xfs_attr_node_removename(
> error = xfs_da3_join(state);
> if (error)
> goto out;
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - goto out;
> - /*
> - * Commit the Btree join operation and start a new trans.
> - */
> - error = xfs_trans_roll_inode(&args->trans, dp);
> - if (error)
> - goto out;
> +
> + dac->flags |= XFS_DAC_DEFER_FINISH;
> + dac->dela_state = XFS_DAS_RM_SHRINK;
> + return -EAGAIN;
> }
>
> +das_rm_shrink:
> + dac->dela_state = XFS_DAS_RM_SHRINK;
> +
> /*
> * If the result is small enough, push it all into the inode.
> */
> if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> - error = xfs_attr_node_shrink(args, state);
> + error = xfs_attr_node_shrink(dac, state);
>
> error = 0;
> out:
> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> index 66575b8..0e8ae1a 100644
> --- a/fs/xfs/libxfs/xfs_attr.h
> +++ b/fs/xfs/libxfs/xfs_attr.h
> @@ -74,6 +74,43 @@ struct xfs_attr_list_context {
> };
>
>
> +/*
> + * ========================================================================
> + * Structure used to pass context around among the delayed routines.
> + * ========================================================================
> + */
> +
> +/*
> + * Enum values for xfs_delattr_context.da_state
> + *
> + * These values are used by delayed attribute operations to keep track of where
> + * they were before they returned -EAGAIN. A return code of -EAGAIN signals the
> + * calling function to roll the transaction, and then recall the subroutine to
> + * finish the operation. The enum is then used by the subroutine to jump back
> + * to where it was and resume executing where it left off.
> + */
> +enum xfs_delattr_state {
> + /* Zero is uninitalized */
> + XFS_DAS_RM_SHRINK = 1, /* We are shrinking the tree */
> + XFS_DAS_RMTVAL_REMOVE, /* We are removing remote value blocks */
> +};
> +
> +/*
> + * Defines for xfs_delattr_context.flags
> + */
> +#define XFS_DAC_DEFER_FINISH 0x1 /* indicates to finish the transaction */
> +
> +/*
> + * Context used for keeping track of delayed attribute operations
> + */
> +struct xfs_delattr_context {
> + struct xfs_da_args *da_args;
> + struct xfs_da_state *da_state;
> + struct xfs_da_state_blk *blk;
> + unsigned int flags;
> + enum xfs_delattr_state dela_state;
> +};
> +
> /*========================================================================
> * Function prototypes for the kernel.
> *========================================================================*/
> @@ -91,6 +128,7 @@ int xfs_attr_set(struct xfs_da_args *args);
> int xfs_attr_set_args(struct xfs_da_args *args);
> int xfs_has_attr(struct xfs_da_args *args);
> int xfs_attr_remove_args(struct xfs_da_args *args);
> +int xfs_attr_remove_iter(struct xfs_delattr_context *dac);
> bool xfs_attr_namecheck(const void *name, size_t length);
>
> #endif /* __XFS_ATTR_H__ */
> --
> 2.7.4
>
