Re: [PATCH v22 11/16] xfs: Add xfs_attr_set_deferred and xfs_attr_remove_deferred

From: Allison Henderson <allison.henderson@oracle.com>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH v22 11/16] xfs: Add xfs_attr_set_deferred and xfs_attr_remove_deferred
Date: Mon, 2 Aug 2021 01:18:40 -0700	[thread overview]
Message-ID: <21db6139-0599-f0de-2950-5e7b19dfae44@oracle.com> (raw)
In-Reply-To: <20210728192418.GE3601443@magnolia>

On 7/28/21 12:24 PM, Darrick J. Wong wrote:
> On Mon, Jul 26, 2021 at 11:20:48PM -0700, Allison Henderson wrote:
>> From: Allison Collins <allison.henderson@oracle.com>
>>
>> These routines set up and queue a new deferred attribute operations.
>> These functions are meant to be called by any routine needing to
>> initiate a deferred attribute operation as opposed to the existing
>> inline operations. New helper function xfs_attr_item_init also added.
>>
>> Finally enable delayed attributes in xfs_attr_set and xfs_attr_remove.
>>
>> Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
>> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>> ---
>>   fs/xfs/libxfs/xfs_attr.c | 70 +++++++++++++++++++++++++++++++++++++++++++++---
>>   fs/xfs/libxfs/xfs_attr.h |  2 ++
>>   fs/xfs/xfs_log.c         | 41 ++++++++++++++++++++++++++++
>>   fs/xfs/xfs_log.h         |  1 +
>>   4 files changed, 111 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
>> index eee219c6..c447c21 100644
>> --- a/fs/xfs/libxfs/xfs_attr.c
>> +++ b/fs/xfs/libxfs/xfs_attr.c
>> @@ -25,6 +25,8 @@
>>   #include "xfs_trans_space.h"
>>   #include "xfs_trace.h"
>>   #include "xfs_attr_item.h"
>> +#include "xfs_attr.h"
>> +#include "xfs_log.h"
>>   
>>   /*
>>    * xfs_attr.c
>> @@ -779,13 +781,19 @@ xfs_attr_set(
>>   		rmt_blks = xfs_attr3_rmt_blocks(mp, XFS_XATTR_SIZE_MAX);
>>   	}
>>   
>> +	if (xfs_hasdelattr(mp)) {
>> +		error = xfs_attr_use_log_assist(mp);
>> +		if (error)
>> +			return error;
>> +	}
>> +
>>   	/*
>>   	 * Root fork attributes can use reserved data blocks for this
>>   	 * operation if necessary
>>   	 */
>>   	error = xfs_trans_alloc_inode(dp, &tres, total, 0, rsvd, &args->trans);
>>   	if (error)
>> -		return error;
>> +		goto drop_incompat;
>>   
>>   	if (args->value || xfs_inode_hasattr(dp)) {
>>   		error = xfs_iext_count_may_overflow(dp, XFS_ATTR_FORK,
>> @@ -803,9 +811,10 @@ xfs_attr_set(
>>   		if (error != -ENOATTR && error != -EEXIST)
>>   			goto out_trans_cancel;
>>   
>> -		error = xfs_attr_set_args(args);
>> +		error = xfs_attr_set_deferred(args);
>>   		if (error)
>>   			goto out_trans_cancel;
>> +
>>   		/* shortform attribute has already been committed */
>>   		if (!args->trans)
>>   			goto out_unlock;
>> @@ -814,7 +823,7 @@ xfs_attr_set(
>>   		if (error != -EEXIST)
>>   			goto out_trans_cancel;
>>   
>> -		error = xfs_attr_remove_args(args);
>> +		error = xfs_attr_remove_deferred(args);
>>   		if (error)
>>   			goto out_trans_cancel;
>>   	}
>> @@ -836,6 +845,9 @@ xfs_attr_set(
>>   	error = xfs_trans_commit(args->trans);
>>   out_unlock:
>>   	xfs_iunlock(dp, XFS_ILOCK_EXCL);
>> +drop_incompat:
>> +	if (xfs_hasdelattr(mp))
> 
> Subtle race here: if you turn this into a debug option and someone
> changes the value from 1 to 0 while this function is running, we'll fail
> to call _drop_incompat here.  You should sample the value at the start
> of the function into a local variable and use that throughout.
I see, will be sure to do that in the next revision then.

> 
>> +		xlog_drop_incompat_feat(mp->m_log);
>>   	return error;
>>   
>>   out_trans_cancel:
>> @@ -844,6 +856,58 @@ xfs_attr_set(
>>   	goto out_unlock;
>>   }
>>   
>> +STATIC int
>> +xfs_attr_item_init(
>> +	struct xfs_da_args	*args,
>> +	unsigned int		op_flags,	/* op flag (set or remove) */
>> +	struct xfs_attr_item	**attr)		/* new xfs_attr_item */
>> +{
>> +
>> +	struct xfs_attr_item	*new;
>> +
>> +	new = kmem_zalloc(sizeof(struct xfs_attr_item), KM_NOFS);
>> +	new->xattri_op_flags = op_flags;
>> +	new->xattri_dac.da_args = args;
>> +
>> +	*attr = new;
>> +	return 0;
>> +}
>> +
>> +/* Sets an attribute for an inode as a deferred operation */
>> +int
>> +xfs_attr_set_deferred(
>> +	struct xfs_da_args	*args)
>> +{
>> +	struct xfs_attr_item	*new;
>> +	int			error = 0;
>> +
>> +	error = xfs_attr_item_init(args, XFS_ATTR_OP_FLAGS_SET, &new);
>> +	if (error)
>> +		return error;
>> +
>> +	xfs_defer_add(args->trans, XFS_DEFER_OPS_TYPE_ATTR, &new->xattri_list);
>> +
>> +	return 0;
>> +}
>> +
>> +/* Removes an attribute for an inode as a deferred operation */
>> +int
>> +xfs_attr_remove_deferred(
>> +	struct xfs_da_args	*args)
>> +{
>> +
>> +	struct xfs_attr_item	*new;
>> +	int			error;
>> +
>> +	error  = xfs_attr_item_init(args, XFS_ATTR_OP_FLAGS_REMOVE, &new);
>> +	if (error)
>> +		return error;
>> +
>> +	xfs_defer_add(args->trans, XFS_DEFER_OPS_TYPE_ATTR, &new->xattri_list);
>> +
>> +	return 0;
>> +}
>> +
>>   /*========================================================================
>>    * External routines when attribute list is inside the inode
>>    *========================================================================*/
>> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
>> index 463b2be..72b0ea5 100644
>> --- a/fs/xfs/libxfs/xfs_attr.h
>> +++ b/fs/xfs/libxfs/xfs_attr.h
>> @@ -527,5 +527,7 @@ 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);
>>   int xfs_attr_calc_size(struct xfs_da_args *args, int *local);
>> +int xfs_attr_set_deferred(struct xfs_da_args *args);
>> +int xfs_attr_remove_deferred(struct xfs_da_args *args);
>>   
>>   #endif	/* __XFS_ATTR_H__ */
>> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
>> index 7c593d9..216de6c 100644
>> --- a/fs/xfs/xfs_log.c
>> +++ b/fs/xfs/xfs_log.c
>> @@ -3948,3 +3948,44 @@ xlog_drop_incompat_feat(
>>   {
>>   	up_read(&log->l_incompat_users);
>>   }
>> +
>> +/*
>> + * Get permission to use log-assisted atomic exchange of file extents.
>> + *
>> + * Callers must not be running any transactions or hold any inode locks, and
>> + * they must release the permission by calling xlog_drop_incompat_feat
>> + * when they're done.
>> + */
>> +int
>> +xfs_attr_use_log_assist(
>> +	struct xfs_mount	*mp)
>> +{
>> +	int			error = 0;
>> +
>> +	/*
>> +	 * Protect ourselves from an idle log clearing the logged xattrs log
>> +	 * incompat feature bit.
>> +	 */
>> +	xlog_use_incompat_feat(mp->m_log);
>> +
>> +	/*
>> +	 * If log-assisted xattrs are already enabled, the caller can use the
>> +	 * log assisted swap functions with the log-incompat reference we got.
>> +	 */
>> +	if (xfs_sb_version_hasdelattr(&mp->m_sb))
>> +		return 0;
>> +
>> +	/* Enable log-assisted xattrs. */
>> +	xfs_warn_once(mp,
>> +"EXPERIMENTAL logged extended attributes feature added. Use at your own risk!");
>> +
>> +	error = xfs_add_incompat_log_feature(mp,
>> +			XFS_SB_FEAT_INCOMPAT_LOG_DELATTR);
>> +	if (error)
>> +		goto drop_incompat;
> 
> Minor bug here (and yes, it's also in the swapext code that I pointed
> you to; apologies for that): We shouldn't print the warning unless the
> feature addition actually succeeds.  IOWs, move the xfs_warn_once()
> here.
No worries, will move the warning down here then.

Thanks for the reviews!
Allison

> 
> (That said, if the feature add fails then the fs is probably going to
> crash soon anyway so it probably doesn't matter...)
> 
> --D
> 
>> +
>> +	return 0;
>> +drop_incompat:
>> +	xlog_drop_incompat_feat(mp->m_log);
>> +	return error;
>> +}
>> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
>> index b274fb9..1e461671 100644
>> --- a/fs/xfs/xfs_log.h
>> +++ b/fs/xfs/xfs_log.h
>> @@ -144,5 +144,6 @@ xfs_lsn_t xlog_grant_push_threshold(struct xlog *log, int need_bytes);
>>   
>>   void xlog_use_incompat_feat(struct xlog *log);
>>   void xlog_drop_incompat_feat(struct xlog *log);
>> +int xfs_attr_use_log_assist(struct xfs_mount *mp);
>>   
>>   #endif	/* __XFS_LOG_H__ */
>> -- 
>> 2.7.4
>>