Re: [PATCH v13 02/10] xfs: Add delay ready attr remove routines

Allison Henderson
2020-10-27T15:44:12Z

On 10/27/20 2:59 AM, Chandan Babu R wrote:
> On Friday 23 October 2020 12:04:27 PM IST 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@oracle.com>
>> ---
>> 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);
>> +}
>> +
>> +/*
>> * 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;
>
> I guess the explicit initialization of "error" can be removed since the
> value returned by the call to xfs_attr_remove_iter() will overwrite it.
Sure, will fix
>
>> + 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;
>>
>> 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)
>> {
>> - 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);
>> 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;
>>
>> /*
>> * 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.
>> + *
>> + * 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;
>> + 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 */
>> + 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;
>
> I don't think it is possible in a real world scenario, but if "state" were
> pointing to allocated memory then the above return value might leak the
> corresponding memory.
Hmm, trying to follow you here.... I'm assuming you meant dela_state
instead of state since that's what controls the switch. The dac
structure is zeroed when allocated to avoid this. Most of the time when
this switch executes, dela_state is zero. I did have to add the
XFS_DAS_UNINIT from the previous suggestion in the last revision though
or it generates warnings.
>
> Apart from the above nit, the remaining changes look good to me.
Ok, thanks for the review!
Allison

>
> Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
>
>> + }
>> +
>> + 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;
>> + }
>>
>> 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"
>>
>
>