[LU-17536] dentry duplication can break rename checks in VFS

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Severity: 3
• Assignee: WC Triage
• Reporter: Alex Zhuravlev

Description

ll_splice_alias() ignores directory dentry unless it's disconnected:

		if ((alias->d_flags & DCACHE_DISCONNECTED) &&
		    S_ISDIR(inode->i_mode))
			/* LASSERT(last_discon == NULL); LU-405, bz 20055 */
			discon_alias = alias;

this can lead to duplicates while VFS (during rename) relies all checks on this hierarchy:

00000080:00200000:1.0:1707475489.059038:0:16032:0:(namei.c:657:ll_splice_alias()) new dentry 0000000032b35fcf 15 for 000000000d62ff8a
00000080:00200000:1.0:1707475489.059039:0:16032:0:(namei.c:87:check_inode_dentry()) inode 000000000d62ff8a
00000080:00200000:1.0:1707475489.059040:0:16032:0:(namei.c:91:check_inode_dentry()) dentry 0000000032b35fcf 15, flags 20000e invalid
00000080:00200000:1.0:1707475489.059040:0:16032:0:(namei.c:91:check_inode_dentry()) dentry 00000000b213e41e 15, flags 28000e 
00000080:00200000:1.0:1707475489.059041:0:16032:0:(namei.c:91:check_inode_dentry()) dentry 0000000094468250 15, flags 28000e