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Index: head/sys/kern/uipc_usrreq.c
===================================================================
--- head/sys/kern/uipc_usrreq.c
+++ head/sys/kern/uipc_usrreq.c
@@ -65,13 +65,13 @@
#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/domain.h>
-#include <sys/fcntl.h>
-#include <sys/malloc.h> /* XXX must be before <sys/file.h> */
#include <sys/eventhandler.h>
+#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/lock.h>
+#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/mount.h>
#include <sys/mutex.h>
@@ -106,9 +106,7 @@
MALLOC_DECLARE(M_FILECAPS);
/*
- * Locking key:
- * (l) Locked using list lock
- * (g) Locked using linkage lock
+ * See unpcb.h for the locking key.
*/
static uma_zone_t unp_zone;
@@ -196,40 +194,31 @@
/*
* Locking and synchronization:
*
- * Three types of locks exist in the local domain socket implementation: a
- * a global linkage rwlock, the mtxpool lock, and per-unpcb mutexes.
- * The linkage lock protects the socket count, global generation number,
- * and stream/datagram global lists.
+ * Several types of locks exist in the local domain socket implementation:
+ * - a global linkage lock
+ * - a global connection list lock
+ * - the mtxpool lock
+ * - per-unpcb mutexes
*
- * The mtxpool lock protects the vnode from being modified while referenced.
- * Lock ordering requires that it be acquired before any unpcb locks.
+ * The linkage lock protects the global socket lists, the generation number
+ * counter and garbage collector state.
*
- * The unpcb lock (unp_mtx) protects all fields in the unpcb. Of particular
- * note is that this includes the unp_conn field. So long as the unpcb lock
- * is held the reference to the unpcb pointed to by unp_conn is valid. If we
- * require that the unpcb pointed to by unp_conn remain live in cases where
- * we need to drop the unp_mtx as when we need to acquire the lock for a
- * second unpcb the caller must first acquire an additional reference on the
- * second unpcb and then revalidate any state (typically check that unp_conn
- * is non-NULL) upon requiring the initial unpcb lock. The lock ordering
- * between unpcbs is the conventional ascending address order. Two helper
- * routines exist for this:
+ * The connection list lock protects the list of referring sockets in a datagram
+ * socket PCB. This lock is also overloaded to protect a global list of
+ * sockets whose buffers contain socket references in the form of SCM_RIGHTS
+ * messages. To avoid recursion, such references are released by a dedicated
+ * thread.
*
- * - unp_pcb_lock2(unp, unp2) - which just acquires the two locks in the
- * safe ordering.
+ * The mtxpool lock protects the vnode from being modified while referenced.
+ * Lock ordering rules require that it be acquired before any PCB locks.
*
- * - unp_pcb_owned_lock2(unp, unp2, freed) - the lock for unp is held
- * when called. If unp is unlocked and unp2 is subsequently freed
- * freed will be set to 1.
- *
- * The helper routines for references are:
- *
- * - unp_pcb_hold(unp): Can be called any time we currently hold a valid
- * reference to unp.
- *
- * - unp_pcb_rele(unp): The caller must hold the unp lock. If we are
- * releasing the last reference, detach must have been called thus
- * unp->unp_socket be NULL.
+ * The unpcb lock (unp_mtx) protects the most commonly referenced fields in the
+ * unpcb. This includes the unp_conn field, which either links two connected
+ * PCBs together (for connected socket types) or points at the destination
+ * socket (for connectionless socket types). The operations of creating or
+ * destroying a connection therefore involve locking multiple PCBs. To avoid
+ * lock order reversals, in some cases this involves dropping a PCB lock and
+ * using a reference counter to maintain liveness.
*
* UNIX domain sockets each have an unpcb hung off of their so_pcb pointer,
* allocated in pru_attach() and freed in pru_detach(). The validity of that
Index: head/sys/sys/unpcb.h
===================================================================
--- head/sys/sys/unpcb.h
+++ head/sys/sys/unpcb.h
@@ -65,30 +65,37 @@
* Stream sockets keep copies of receive sockbuf sb_cc and sb_mbcnt
* so that changes in the sockbuf may be computed to modify
* back pressure on the sender accordingly.
+ *
+ * Locking key:
+ * (a) Atomic
+ * (c) Constant
+ * (g) Locked using linkage lock
+ * (l) Locked using list lock
+ * (p) Locked using pcb lock
*/
LIST_HEAD(unp_head, unpcb);
struct unpcb {
/* Cache line 1 */
- struct mtx unp_mtx; /* mutex */
- struct unpcb *unp_conn; /* control block of connected socket */
- volatile u_int unp_refcount;
- short unp_flags; /* flags */
- short unp_gcflag; /* Garbage collector flags. */
- struct sockaddr_un *unp_addr; /* bound address of socket */
- struct socket *unp_socket; /* pointer back to socket */
+ struct mtx unp_mtx; /* PCB mutex */
+ struct unpcb *unp_conn; /* (p) connected socket */
+ volatile u_int unp_refcount; /* (a, p) atomic refcount */
+ short unp_flags; /* (p) PCB flags */
+ short unp_gcflag; /* (g) Garbage collector flags */
+ struct sockaddr_un *unp_addr; /* (p) bound address of socket */
+ struct socket *unp_socket; /* (c) pointer back to socket */
/* Cache line 2 */
- struct vnode *unp_vnode; /* if associated with file */
- struct xucred unp_peercred; /* peer credentials, if applicable */
- LIST_ENTRY(unpcb) unp_reflink; /* link in unp_refs list */
- LIST_ENTRY(unpcb) unp_link; /* glue on list of all PCBs */
- struct unp_head unp_refs; /* referencing socket linked list */
- unp_gen_t unp_gencnt; /* generation count of this instance */
- struct file *unp_file; /* back-pointer to file for gc. */
- u_int unp_msgcount; /* references from message queue */
- u_int unp_gcrefs; /* garbage collector refcount */
- ino_t unp_ino; /* fake inode number */
- LIST_ENTRY(unpcb) unp_dead; /* link in dead list */
+ struct vnode *unp_vnode; /* (p) associated file if applicable */
+ struct xucred unp_peercred; /* (p) peer credentials if applicable */
+ LIST_ENTRY(unpcb) unp_reflink; /* (l) link in unp_refs list */
+ LIST_ENTRY(unpcb) unp_link; /* (g) glue on list of all PCBs */
+ struct unp_head unp_refs; /* (l) referencing socket linked list */
+ unp_gen_t unp_gencnt; /* (g) generation count of this item */
+ struct file *unp_file; /* (g) back-pointer to file for gc */
+ u_int unp_msgcount; /* (g) references from message queue */
+ u_int unp_gcrefs; /* (g) garbage collector refcount */
+ ino_t unp_ino; /* (g) fake inode number */
+ LIST_ENTRY(unpcb) unp_dead; /* (g) link in dead list */
} __aligned(CACHE_LINE_SIZE);
/*

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