dlm: fix race between final callback and remove

This patch fixes the following issue:

node 1 is dir
node 2 is master
node 3 is other

1->2: unlock
2: put final lkb, rsb moved to toss
2->1: unlock_reply
1: queue lkb callback with EUNLOCK
2->1: remove
1: receive_remove ignored (rsb on keep because of queued lkb callback)
1: complete lkb callback, put_lkb, move rsb to toss
3->1: lookup
1->3: lookup_reply master=2
3->2: request
2->3: request_reply EBADR

In summary:
An unexpected lkb reference causes the rsb to remain on the wrong list.
The rsb being on the wrong list causes receive_remove to be ignored.
An ignored receive_remove causes inconsistent dir and master state.

This sequence requires an unusually long delay in delivering the unlock
callback, because the remove message from 2->1 usually happens after
some seconds.  So, it's not known exactly how frequently this sequence
occurs in pratice.  It's possible that the same end result could also
have another unknown cause.

The solution for this issue is to further separate callback state
from the lkb, so that an lkb reference (and from that, an rsb ref)
are not held while a callback remains queued.  Then, within the
unlock_reply, the lkb will be freed and the rsb moved to the toss
list. So, the receive_remove will not be ignored.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

1 files changed, 36 insertions, 24 deletions

diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index a9137c90f348..cda1526fd15b 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -16,6 +16,7 @@
  * This is the main header file to be included in each DLM source file.
  */
 
+#include <uapi/linux/dlm_device.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/types.h>
@@ -204,8 +205,7 @@ struct dlm_args {
 #define DLM_IFL_OVERLAP_CANCEL_BIT 20
 #define DLM_IFL_ENDOFLIFE_BIT	21
 #define DLM_IFL_DEADLOCK_CANCEL_BIT 24
-#define DLM_IFL_CB_PENDING_BIT	25
-#define __DLM_IFL_MAX_BIT	DLM_IFL_CB_PENDING_BIT
+#define __DLM_IFL_MAX_BIT	DLM_IFL_DEADLOCK_CANCEL_BIT
 
 /* lkb_dflags */
 
@@ -217,12 +217,45 @@ struct dlm_args {
 #define DLM_CB_CAST		0x00000001
 #define DLM_CB_BAST		0x00000002
 
+/* much of this is just saving user space pointers associated with the
+ * lock that we pass back to the user lib with an ast
+ */
+
+struct dlm_user_args {
+	struct dlm_user_proc	*proc; /* each process that opens the lockspace
+					* device has private data
+					* (dlm_user_proc) on the struct file,
+					* the process's locks point back to it
+					*/
+	struct dlm_lksb		lksb;
+	struct dlm_lksb __user	*user_lksb;
+	void __user		*castparam;
+	void __user		*castaddr;
+	void __user		*bastparam;
+	void __user		*bastaddr;
+	uint64_t		xid;
+};
+
 struct dlm_callback {
 	uint32_t		flags;		/* DLM_CBF_ */
 	int			sb_status;	/* copy to lksb status */
 	uint8_t			sb_flags;	/* copy to lksb flags */
 	int8_t			mode; /* rq mode of bast, gr mode of cast */
-	int			copy_lvb;
+	bool			copy_lvb;
+	struct dlm_lksb		*lkb_lksb;
+	unsigned char		lvbptr[DLM_USER_LVB_LEN];
+
+	union {
+		void			*astparam;	/* caller's ast arg */
+		struct dlm_user_args	ua;
+	};
+	struct work_struct	work;
+	void			(*bastfn)(void *astparam, int mode);
+	void			(*astfn)(void *astparam);
+	char			res_name[DLM_RESNAME_MAXLEN];
+	size_t			res_length;
+	uint32_t		ls_id;
+	uint32_t		lkb_id;
 
 	struct list_head	list;
 	struct kref		ref;
@@ -256,10 +289,6 @@ struct dlm_lkb {
 	struct list_head	lkb_ownqueue;	/* list of locks for a process */
 	ktime_t			lkb_timestamp;
 
-	spinlock_t		lkb_cb_lock;
-	struct work_struct	lkb_cb_work;
-	struct list_head	lkb_cb_list; /* for ls_cb_delay or proc->asts */
-	struct list_head	lkb_callbacks;
 	struct dlm_callback	*lkb_last_cast;
 	struct dlm_callback	*lkb_last_cb;
 	int			lkb_last_bast_mode;
@@ -688,23 +717,6 @@ struct dlm_ls {
 #define LSFL_CB_DELAY		9
 #define LSFL_NODIR		10
 
-/* much of this is just saving user space pointers associated with the
-   lock that we pass back to the user lib with an ast */
-
-struct dlm_user_args {
-	struct dlm_user_proc	*proc; /* each process that opens the lockspace
-					  device has private data
-					  (dlm_user_proc) on the struct file,
-					  the process's locks point back to it*/
-	struct dlm_lksb		lksb;
-	struct dlm_lksb __user	*user_lksb;
-	void __user		*castparam;
-	void __user		*castaddr;
-	void __user		*bastparam;
-	void __user		*bastaddr;
-	uint64_t		xid;
-};
-
 #define DLM_PROC_FLAGS_CLOSING 1
 #define DLM_PROC_FLAGS_COMPAT  2