From 5bdef466851e39ba752634cbea68e5ea24ccfb24 Mon Sep 17 00:00:00 2001 From: Cen Zhang Date: Tue, 27 Oct 2026 12:31:44 +0800 Subject: [PATCH] ocfs2: keep locking_state within the cluster connection lifetime The locking_state reader calls ocfs2_dlm_lvb() through the selected cluster stack. Its debug-object reference keeps the tracking list alive, but does not keep that stack selected without a cluster connection. DLM initialization publishes the file before establishing its connection, and DLM shutdown drops the connection while the file still exists. Both the mount error unwind in ocfs2_mount_volume() and ocfs2_dismount_volume() remove the debugfs subtree only after ocfs2_dlm_shutdown() has returned. Whenever the disconnect releases the last stack reference, which is the case for a failed mount and for any unmount without a pending hangup, a concurrent reader dereferences a NULL active_stack: Mount error unwind Debugfs reader ------------------ -------------- ocfs2_mount_volume(): out_dlm ocfs2_dlm_shutdown() disconnect last cluster clear active_stack read locking_state ocfs2_dlm_seq_show() ocfs2_dlm_lvb() dereference active_stack fill_super(): out_debugfs remove debugfs subtree Publish the debug files only after the connection and the mount lock resources are initialized, so a failed DLM initialization has no debug reference to drop. Remove them again in the common DLM shutdown helper before the connection is dropped: debugfs removal waits for readers that are inside the file operations, and the parent directory is still present at that point in every caller. This covers the mount error unwind, the ocfs2_fill_super() failures after a successful mount that dismount with mnt_err set, and unmounts whose disconnect releases the stack directly. Only the relevant frames of the report are kept: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] RIP: 0010:ocfs2_dlm_lvb+0x38/0xf0 Call Trace: ocfs2_dlm_seq_show+0x36a/0xb70 seq_read_iter+0x480/0x1110 seq_read+0x362/0x5a0 full_proxy_read+0x11f/0x180 vfs_read+0x1a0/0xc20 ksys_read+0x111/0x200 Link: https://lore.kernel.org/pm-ocfs2-objects-candidate-0011-v7-61e3ef8b1ad44ac2e817@gmail.com Fixes: 286eaa95c5c5 ("ocfs2: Break out stackglue into modules.") Signed-off-by: Cen Zhang Signed-off-by: Andrew Morton Reviewed-by: Joseph Qi Assisted-by: LLM Cc: Mark Fasheh Cc: Joel Becker Cc: Heming Zhao Cc: Jia-Ju Bai Cc: Cc: --- fs/ocfs2/dlmglue.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c index 88d946466083..412ab0808c59 100644 --- a/fs/ocfs2/dlmglue.c +++ b/fs/ocfs2/dlmglue.c @@ -3356,6 +3356,14 @@ static void ocfs2_dlm_shutdown_debug(struct ocfs2_super *osb) { struct ocfs2_dlm_debug *dlm_debug = osb->osb_dlm_debug; + /* + * Drain the readers before the cluster stack goes away: the + * locking_state reader resolves ocfs2_dlm_lvb() through the + * stack. Every caller removes the parent directory later. + */ + debugfs_lookup_and_remove("locking_state", osb->osb_debug_root); + debugfs_lookup_and_remove("locking_filter", osb->osb_debug_root); + if (dlm_debug) ocfs2_put_dlm_debug(dlm_debug); } @@ -3370,8 +3378,6 @@ int ocfs2_dlm_init(struct ocfs2_super *osb) goto local; } - ocfs2_dlm_init_debug(osb); - /* launch downconvert thread */ osb->dc_task = kthread_run(ocfs2_downconvert_thread, osb, "ocfs2dc-%s", osb->uuid_str); @@ -3411,9 +3417,10 @@ int ocfs2_dlm_init(struct ocfs2_super *osb) ocfs2_orphan_scan_lock_res_init(&osb->osb_orphan_scan.os_lockres, osb); osb->cconn = conn; + if (conn) + ocfs2_dlm_init_debug(osb); bail: if (status < 0) { - ocfs2_dlm_shutdown_debug(osb); if (osb->dc_task) kthread_stop(osb->dc_task); } @@ -3443,10 +3450,11 @@ void ocfs2_dlm_shutdown(struct ocfs2_super *osb, ocfs2_lock_res_free(&osb->osb_orphan_scan.os_lockres); if (osb->cconn) { + /* The disconnect below may release the selected stack. */ + ocfs2_dlm_shutdown_debug(osb); + ocfs2_cluster_disconnect(osb->cconn, hangup_pending); osb->cconn = NULL; - - ocfs2_dlm_shutdown_debug(osb); } }