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

[Allison Henderson <allison.henderson@oracle.com>]

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"
>>
> 
>