Commit a4b8917b authored May 11, 2022 by Dave Chinner Committed by Dave Chinner May 11, 2022

xfs: avoid empty xattr transaction when attrs are inline



generic/642 triggered a reproducable assert failure in
xlog_cil_commit() that resulted from a xfs_attr_set() committing
an empty but dirty transaction. When the CIL is empty and this
occurs, xlog_cil_commit() tries a background push and this triggers
a "pushing an empty CIL" assert.

XFS: Assertion failed: !list_empty(&cil->xc_cil), file: fs/xfs/xfs_log_cil.c, line: 1274
Call Trace:
 <TASK>
 xlog_cil_commit+0xa5a/0xad0
 __xfs_trans_commit+0xb8/0x330
 xfs_trans_commit+0x10/0x20
 xfs_attr_set+0x3e2/0x4c0
 xfs_xattr_set+0x8d/0xe0
 __vfs_setxattr+0x6b/0x90
 __vfs_setxattr_noperm+0x76/0x220
 __vfs_setxattr_locked+0xdf/0x100
 vfs_setxattr+0x94/0x170
 setxattr+0x110/0x200
 path_setxattr+0xbf/0xe0
 __x64_sys_setxattr+0x2b/0x30
 do_syscall_64+0x35/0x80

The problem is related to the breakdown of attribute addition in
xfs_attr_set_iter() and how it is called from deferred operations.
When we have a pure leaf xattr insert, we add the xattr to the leaf
and set the next state to XFS_DAS_FOUND_LBLK and return -EAGAIN.
This requeues the xattr defered work, rolls the transaction and
runs xfs_attr_set_iter() again. This then checks the xattr for
being remote (it's not) and whether a replace op is being done (this
is a create op) and if neither are true it returns without having
done anything.

xfs_xattri_finish_update() then unconditionally sets the transaction
dirty, and the deferops finishes and returns to __xfs_trans_commit()
which sees the transaction dirty and tries to commit it by calling
xlog_cil_commit(). The transaction is empty, and then the assert
fires if this happens when the CIL is empty.

This patch addresses the structure of xfs_attr_set_iter() that
requires re-entry on leaf add even when nothing will be done. This
gets rid of the trailing empty transaction and so doesn't trigger
the XFS_TRANS_DIRTY assignment in xfs_xattri_finish_update()
incorrectly. Addressing that is for a different patch.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison <Henderson&lt;allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

parent c5218a7c

fs/xfs/libxfs/xfs_attr.c

+19 −20

Original line number	Diff line number	Diff line
		@@ -314,6 +314,7 @@ xfs_attr_leaf_addname(
		{
		struct xfs_da_args *args = attr->xattri_da_args;
		struct xfs_inode *dp = args->dp;
		enum xfs_delattr_state next_state = XFS_DAS_UNINIT;
		int error;

		if (xfs_attr_is_leaf(dp)) {
		@@ -334,37 +335,35 @@ xfs_attr_leaf_addname(
		* when we come back, we'll be a node, so we'll fall
		* down into the node handling code below
		*/
		trace_xfs_attr_set_iter_return(
		attr->xattri_dela_state, args->dp);
		return -EAGAIN;
		error = -EAGAIN;
		goto out;
		}

		if (error)
		return error;

		attr->xattri_dela_state = XFS_DAS_FOUND_LBLK;
		next_state = XFS_DAS_FOUND_LBLK;
		} else {
		error = xfs_attr_node_addname_find_attr(attr);
		if (error)
		return error;

		next_state = XFS_DAS_FOUND_NBLK;
		error = xfs_attr_node_addname(attr);
		}
		if (error)
		return error;

		/*
		* If addname was successful, and we dont need to alloc or
		* remove anymore blks, we're done.
		* We need to commit and roll if we need to allocate remote xattr blocks
		* or perform more xattr manipulations. Otherwise there is nothing more
		* to do and we can return success.
		*/
		if (!args->rmtblkno &&
		!(args->op_flags & XFS_DA_OP_RENAME))
		return 0;

		attr->xattri_dela_state = XFS_DAS_FOUND_NBLK;
		if (args->rmtblkno \|\|
		(args->op_flags & XFS_DA_OP_RENAME)) {
		attr->xattri_dela_state = next_state;
		error = -EAGAIN;
		}

		out:
		trace_xfs_attr_leaf_addname_return(attr->xattri_dela_state, args->dp);
		return -EAGAIN;
		return error;
		}

		/*