On Thu, Oct 22, 2020 at 11:34:27PM -0700, Allison Henderson 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. A new XFS_DAC_DEFER_FINISH flag is used to finish the
> transaction where ever the existing code used to.
>
> Calls to xfs_attr_rmtval_remove are replaced with the delay ready
> version __xfs_attr_rmtval_remove. We will rename
> __xfs_attr_rmtval_remove back to xfs_attr_rmtval_remove when we are
> done.
>
> xfs_attr_rmtval_remove itself is still in use by the set routines (used
> during a rename). For reasons of preserving existing function, we
> modify xfs_attr_rmtval_remove to call xfs_defer_finish when the flag is
> set. Similar to how xfs_attr_remove_args does here. Once we transition
> the set routines to be delay ready, xfs_attr_rmtval_remove is no longer
> used and will be removed.
>
> 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. See xfs_attr.h for a more
> detailed diagram of the states.
>
> Signed-off-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_attr.c | 200 +++++++++++++++++++++++++++++-----------
> fs/xfs/libxfs/xfs_attr.h | 72 +++++++++++++++
> fs/xfs/libxfs/xfs_attr_leaf.c | 2 +-
> fs/xfs/libxfs/xfs_attr_remote.c | 37 ++++----
> fs/xfs/libxfs/xfs_attr_remote.h | 2 +-
> fs/xfs/xfs_attr_inactive.c | 2 +-
> 6 files changed, 241 insertions(+), 74 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index f4d39bf..6ca94cb 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -53,7 +53,7 @@ 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_iter(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);
> @@ -264,6 +264,33 @@ xfs_attr_set_shortform(
> }
>
> /*
> + * Checks to see if a delayed attribute transaction should be rolled. If so,
> + * also checks for a defer finish. Transaction is finished and rolled as
> + * needed, and returns true of false if the delayed operation should continue.
> + */
> +int
> +xfs_attr_trans_roll(
> + struct xfs_delattr_context *dac)
> +{
> + struct xfs_da_args *args = dac->da_args;
> + int error = 0;
> +
> + if (dac->flags & XFS_DAC_DEFER_FINISH) {
> + /*
> + * The caller wants us to finish all the deferred ops so that we
> + * avoid pinning the log tail with a large number of deferred
> + * ops.
> + */
> + dac->flags &= ~XFS_DAC_DEFER_FINISH;
> + error = xfs_defer_finish(&args->trans);
> + if (error)
> + return error;
> + }
> +
> + return xfs_trans_roll_inode(&args->trans, args->dp);
> +}
(Mostly ignoring these functions since they all go away by the end of
the patchset...)
> +
> +/*
> * Set the attribute specified in @args.
> */
> int
> @@ -364,23 +391,54 @@ xfs_has_attr(
> */
> int
> xfs_attr_remove_args(
> - struct xfs_da_args *args)
> + struct xfs_da_args *args)
> {
> - struct xfs_inode *dp = args->dp;
> - int error;
> + int error = 0;
> + struct xfs_delattr_context dac = {
> + .da_args = args,
> + };
> +
> + do {
> + error = xfs_attr_remove_iter(&dac);
> + if (error != -EAGAIN)
> + break;
> +
> + error = xfs_attr_trans_roll(&dac);
> + if (error)
> + return error;
> +
> + } 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;
> +
> + if (dac->dela_state == XFS_DAS_RM_SHRINK)
> + goto node;
>
Might as well just make this part of the if statement dispatch:
if (dac->dela_state == XFS_DAS_RM_SHRINK)
return xfs_attr_node_removename_iter(dac);
else if (!xfs_inode_hasattr(dp))
return -ENOATTR;
> if (!xfs_inode_hasattr(dp)) {
> - error = -ENOATTR;
> + return -ENOATTR;
> } else if (dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL) {
> ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
> - error = xfs_attr_shortform_remove(args);
> + return xfs_attr_shortform_remove(args);
> } else if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> - error = xfs_attr_leaf_removename(args);
> - } else {
> - error = xfs_attr_node_removename(args);
> + return xfs_attr_leaf_removename(args);
> }
> -
> - return error;
> +node:
> + return xfs_attr_node_removename_iter(dac);
> }
>
> /*
> @@ -1178,10 +1236,11 @@ xfs_attr_leaf_mark_incomplete(
> */
> 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)
AFAICT *state == &dac->da_state by the end of the series; can you
should remove this argument too?
> {
> - int error;
> + struct xfs_da_args *args = dac->da_args;
> + int error;
>
> error = xfs_attr_node_hasname(args, state);
> if (error != -EEXIST)
> @@ -1191,6 +1250,12 @@ int xfs_attr_node_removename_setup(
> ASSERT((*state)->path.blk[(*state)->path.active - 1].magic ==
> XFS_ATTR_LEAF_MAGIC);
>
> + /*
> + * Store state in the context incase we need to cycle out the
> + * transaction
> + */
> + dac->da_state = *state;
> +
> if (args->rmtblkno > 0) {
> error = xfs_attr_leaf_mark_incomplete(args, *state);
It doesn't make a lot of logical sense to me "we marked the attr
incomplete to hide it" is the same state (UNINIT) as "we haven't done
anything yet".
> if (error)
> @@ -1203,13 +1268,16 @@ int xfs_attr_node_removename_setup(
> }
>
> STATIC int
> -xfs_attr_node_remove_rmt(
> - struct xfs_da_args *args,
> - struct xfs_da_state *state)
> +xfs_attr_node_remove_rmt (
> + struct xfs_delattr_context *dac,
> + struct xfs_da_state *state)
> {
> - int error = 0;
> + 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(dac);
> if (error)
> return error;
>
> @@ -1221,21 +1289,27 @@ xfs_attr_node_remove_rmt(
> }
>
> /*
> - * Remove a name from a B-tree attribute list.
> + * Step through removeing a name from a B-tree attribute list.
> *
> * 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_remove_step(
> - struct xfs_da_args *args,
> - struct xfs_da_state *state)
> + struct xfs_delattr_context *dac)
> {
> - struct xfs_da_state_blk *blk;
> - int retval, error;
> - struct xfs_inode *dp = args->dp;
> + struct xfs_da_args *args = dac->da_args;
> + struct xfs_da_state *state;
> + struct xfs_da_state_blk *blk;
> + int retval, error = 0;
>
> + state = dac->da_state;
Might as well initialize this when you declare state above.
>
> /*
> * If there is an out-of-line value, de-allocate the blocks.
> @@ -1243,7 +1317,10 @@ xfs_attr_node_remove_step(
> * overflow the maximum size of a transaction and/or hit a deadlock.
> */
> if (args->rmtblkno > 0) {
> - error = xfs_attr_node_remove_rmt(args, state);
> + /*
> + * May return -EAGAIN. Remove blocks until args->rmtblkno == 0
> + */
> + error = xfs_attr_node_remove_rmt(dac, state);
> if (error)
> return error;
> }
> @@ -1257,21 +1334,18 @@ xfs_attr_node_remove_step(
> xfs_da3_fixhashpath(state, &state->path);
>
> /*
> - * Check to see if the tree needs to be collapsed.
> + * Check to see if the tree needs to be collapsed. Set the flag to
> + * indicate that the calling function needs to move the to shrink
> + * operation
> */
> if (retval && (state->path.active > 1)) {
> error = xfs_da3_join(state);
> if (error)
> return error;
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - return error;
> - /*
> - * Commit the Btree join operation and start a new trans.
> - */
> - error = xfs_trans_roll_inode(&args->trans, dp);
> - if (error)
> - return error;
> +
> + dac->flags |= XFS_DAC_DEFER_FINISH;
> + dac->dela_state = XFS_DAS_RM_SHRINK;
> + return -EAGAIN;
> }
>
> return error;
> @@ -1282,31 +1356,53 @@ xfs_attr_node_remove_step(
> *
> * This routine will find the blocks of the name to remove, remove them and
> * shirnk the tree if needed.
"...and shrink the tree..."
> + *
> + * 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)
> +xfs_attr_node_removename_iter(
> + struct xfs_delattr_context *dac)
> {
> - struct xfs_da_state *state;
> - int error;
> - struct xfs_inode *dp = args->dp;
> + struct xfs_da_args *args = dac->da_args;
> + struct xfs_da_state *state;
> + int error;
> + struct xfs_inode *dp = args->dp;
>
> trace_xfs_attr_node_removename(args);
> + state = dac->da_state;
>
> - error = xfs_attr_node_removename_setup(args, &state);
> - if (error)
> - goto out;
> + if ((dac->flags & XFS_DAC_NODE_RMVNAME_INIT) == 0) {
> + dac->flags |= XFS_DAC_NODE_RMVNAME_INIT;
Can we determine if it's necessary to call _removename_setup by checking
dac->da_state directly instead of having a flag?
> + error = xfs_attr_node_removename_setup(dac, &state);
> + if (error)
> + goto out;
> + }
>
> - error = xfs_attr_node_remove_step(args, state);
> - if (error)
> - goto out;
> + switch (dac->dela_state) {
> + case XFS_DAS_UNINIT:
> + error = xfs_attr_node_remove_step(dac);
> + if (error)
> + break;
>
> - /*
> - * 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);
> + /* do not break, proceed to shrink if needed */
/* fall through */
...because otherwise the static checkers will get mad.
(Well clang will anyway because gcc, llvm, and the C18 body all have
different incompatible ideas of what should be the magic tag that
signals an intentional fall through, but this should at least be
consistent with the rest of xfs.)
> + case 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);
>
> + break;
> + default:
> + ASSERT(0);
> + return -EINVAL;
> + }
> +
> + if (error == -EAGAIN)
> + return error;
> out:
> if (state)
> xfs_da_state_free(state);
> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> index 3e97a93..64dcf0f 100644
> --- a/fs/xfs/libxfs/xfs_attr.h
> +++ b/fs/xfs/libxfs/xfs_attr.h
> @@ -74,6 +74,74 @@ struct xfs_attr_list_context {
> };
>
>
> +/*
> + * ========================================================================
> + * Structure used to pass context around among the delayed routines.
> + * ========================================================================
> + */
> +
> +/*
> + * 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_attr_node_removename()
> + * │
> + * v
> + * need to
> + * shrink tree? ─n─┐
> + * │ │
> + * y │
> + * │ │
> + * v │
> + * XFS_DAS_RM_SHRINK │
> + * │ │
> + * v │
> + * done <─────┘
> + *
> + */
> +
> +/*
> + * 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 {
> + XFS_DAS_UNINIT = 0, /* No state has been set yet */
> + XFS_DAS_RM_SHRINK, /* We are shrinking the tree */
> +};
> +
> +/*
> + * Defines for xfs_delattr_context.flags
> + */
> +#define XFS_DAC_DEFER_FINISH 0x01 /* finish the transaction */
> +#define XFS_DAC_NODE_RMVNAME_INIT 0x02 /* xfs_attr_node_removename init */
> +
> +/*
> + * Context used for keeping track of delayed attribute operations
> + */
> +struct xfs_delattr_context {
> + struct xfs_da_args *da_args;
> +
> + /* Used in xfs_attr_node_removename to roll through removing blocks */
> + struct xfs_da_state *da_state;
> +
> + /* Used to keep track of current state of delayed operation */
> + unsigned int flags;
> + enum xfs_delattr_state dela_state;
> +};
> +
> /*========================================================================
> * Function prototypes for the kernel.
> *========================================================================*/
> @@ -91,6 +159,10 @@ 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);
> +int xfs_attr_trans_roll(struct xfs_delattr_context *dac);
> bool xfs_attr_namecheck(const void *name, size_t length);
> +void xfs_delattr_context_init(struct xfs_delattr_context *dac,
> + struct xfs_da_args *args);
>
> #endif /* __XFS_ATTR_H__ */
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index bb128db..338377e 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -19,8 +19,8 @@
> #include "xfs_bmap_btree.h"
> #include "xfs_bmap.h"
> #include "xfs_attr_sf.h"
> -#include "xfs_attr_remote.h"
> #include "xfs_attr.h"
> +#include "xfs_attr_remote.h"
> #include "xfs_attr_leaf.h"
> #include "xfs_error.h"
> #include "xfs_trace.h"
> diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
> index 48d8e9c..1426c15 100644
> --- a/fs/xfs/libxfs/xfs_attr_remote.c
> +++ b/fs/xfs/libxfs/xfs_attr_remote.c
> @@ -674,10 +674,12 @@ xfs_attr_rmtval_invalidate(
> */
> int
> xfs_attr_rmtval_remove(
> - struct xfs_da_args *args)
> + struct xfs_da_args *args)
> {
> - int error;
> - int retval;
> + int error;
> + struct xfs_delattr_context dac = {
> + .da_args = args,
> + };
>
> trace_xfs_attr_rmtval_remove(args);
>
> @@ -685,19 +687,17 @@ xfs_attr_rmtval_remove(
> * Keep de-allocating extents until the remote-value region is gone.
> */
> do {
> - retval = __xfs_attr_rmtval_remove(args);
> - if (retval && retval != -EAGAIN)
> - return retval;
> + error = __xfs_attr_rmtval_remove(&dac);
> + if (error != -EAGAIN)
> + break;
>
> - /*
> - * Close out trans and start the next one in the chain.
> - */
> - error = xfs_trans_roll_inode(&args->trans, args->dp);
> + error = xfs_attr_trans_roll(&dac);
> if (error)
> return error;
> - } while (retval == -EAGAIN);
>
> - return 0;
> + } while (true);
> +
> + return error;
> }
>
> /*
> @@ -707,9 +707,10 @@ xfs_attr_rmtval_remove(
> */
> int
> __xfs_attr_rmtval_remove(
> - struct xfs_da_args *args)
> + struct xfs_delattr_context *dac)
> {
> - int error, done;
> + struct xfs_da_args *args = dac->da_args;
> + int error, done;
>
> /*
> * Unmap value blocks for this attr.
> @@ -719,12 +720,10 @@ __xfs_attr_rmtval_remove(
> if (error)
> return error;
>
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - return error;
> -
> - if (!done)
> + if (!done) {
> + dac->flags |= XFS_DAC_DEFER_FINISH;
> return -EAGAIN;
What state are we in when we return -EAGAIN here?
[jumps back to his whole-branch diff]
Hm, oh, I see, the next state could be a number of things--
RM_LBLK if we're removing an old remote value from a leaf block as part
of an attr set operation; or
RM_NBLK if we're removing an old remote value from a node block as part
of an attr set operation; and
UNINIT if we're removing a remote value as part of an attr set
operation.
Oh! For the first two, it looks to me as though either we're already in
the state we're setting (RM_[LN]BLK) or we were in either of the
FLIP_[LN]FLAG state.
I think it would make more sense if you set the state before calling the
rmtval_remove function, and leave a comment here saying that the caller
is responsible for figuring out the next state.
For removals, I wonder if we should have advanced beyond UNINIT by the
time we get here? I think you've added the minimum states that are
necessary to resume work after a transaction roll, but from this and the
next patch I feel like we do a lot of work while dela_state == UNINIT.
FWIW I will be taking a close look at all the new 'return -EAGAIN'
statements to see if I can tell what state we're in when we trigger a
transaction roll.
--D
> + }
>
> return error;
> }
> diff --git a/fs/xfs/libxfs/xfs_attr_remote.h b/fs/xfs/libxfs/xfs_attr_remote.h
> index 9eee615..002fd30 100644
> --- a/fs/xfs/libxfs/xfs_attr_remote.h
> +++ b/fs/xfs/libxfs/xfs_attr_remote.h
> @@ -14,5 +14,5 @@ int xfs_attr_rmtval_remove(struct xfs_da_args *args);
> int xfs_attr_rmtval_stale(struct xfs_inode *ip, struct xfs_bmbt_irec *map,
> xfs_buf_flags_t incore_flags);
> int xfs_attr_rmtval_invalidate(struct xfs_da_args *args);
> -int __xfs_attr_rmtval_remove(struct xfs_da_args *args);
> +int __xfs_attr_rmtval_remove(struct xfs_delattr_context *dac);
> #endif /* __XFS_ATTR_REMOTE_H__ */
> diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c
> index bfad669..aaa7e66 100644
> --- a/fs/xfs/xfs_attr_inactive.c
> +++ b/fs/xfs/xfs_attr_inactive.c
> @@ -15,10 +15,10 @@
> #include "xfs_da_format.h"
> #include "xfs_da_btree.h"
> #include "xfs_inode.h"
> +#include "xfs_attr.h"
> #include "xfs_attr_remote.h"
> #include "xfs_trans.h"
> #include "xfs_bmap.h"
> -#include "xfs_attr.h"
> #include "xfs_attr_leaf.h"
> #include "xfs_quota.h"
> #include "xfs_dir2.h"
> --
> 2.7.4
>
