[PATCH 01/17] xfs: avoid empty xattr transaction when attrs are inline

Dave Chinner
2022-05-06T09:46:10Z

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<allison.henderson@oracle.com>
---
fs/xfs/libxfs/xfs_attr.c | 39 +++++++++++++++++++--------------------
1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index 48b7e7efbb30..b3d918195160 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -315,6 +315,7 @@ 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)) {
@@ -335,37 +336,35 @@ 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.
- */
- if (!args->rmtblkno &&
- !(args->op_flags & XFS_DA_OP_RENAME))
- return 0;
+ }
+ if (error)
+ return error;

- attr->xattri_dela_state = XFS_DAS_FOUND_NBLK;
+ /*
+ * 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)) {
+ 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;
}

/*
--
2.35.1