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Add a reference count to struct inpcb, which may be explicitly

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incremented using in_pcbref(), and decremented using in_pcbfree()
or inpcbrele().  Protocols using only current in_pcballoc() and
in_pcbfree() calls will see the same semantics, but it is now
possible for TCP to call in_pcbref() and in_pcbrele() to prevent
an inpcb from being freed when both tcbinfo and per-inpcb locks
are released.  This makes it possible to safely transition from
holding only the inpcb lock to both tcbinfo and inpcb lock
without re-looking up a connection in the input path, timer
path, etc.

Notice that in_pcbrele() does not unlock the connection after
decrementing the refcount, if the connection remains, so that
the caller can continue to use it; in_pcbrele() returns a flag
indicating whether or not the inpcb pointer is still valid, and
in_pcbfee() is now a simple wrapper around in_pcbrele().

MFC after:	1 month
Discussed with:	bz, kmacy
Reviewed by:	bz, gnn, kmacy
Tested by:	kmacy
This commit is contained in:
Robert Watson 2008-12-08 20:18:50 +00:00
parent 9bd2cbe43f
commit 28696211d6
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=185773
2 changed files with 85 additions and 12 deletions
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94
sys/netinet/in_pcb.c
View File

@ -1,7 +1,7 @@
/*-
* Copyright (c) 1982, 1986, 1991, 1993, 1995
* The Regents of the University of California.
* Copyright (c) 2007 Robert N. M. Watson
* Copyright (c) 2007-2008 Robert N. M. Watson
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -238,6 +238,7 @@ in_pcballoc(struct socket *so, struct inpcbinfo *pcbinfo)
#endif
INP_WLOCK(inp);
inp->inp_gencnt = ++pcbinfo->ipi_gencnt;
inp->inp_refcount = 1; /* Reference from the inpcbinfo */
#if defined(IPSEC) || defined(MAC)
out:
@ -872,14 +873,10 @@ in_pcbdisconnect(struct inpcb *inp)
}
/*
* Historically, in_pcbdetach() included the functionality now found in
* in_pcbfree() and in_pcbdrop(). They are now broken out to reflect the
* more complex life cycle of TCP.
*
* in_pcbdetach() is responsibe for disconnecting the socket from an inpcb.
* in_pcbdetach() is responsibe for disassociating a socket from an inpcb.
* For most protocols, this will be invoked immediately prior to calling
* in_pcbfree(). However, for TCP the inpcb may significantly outlive the
* socket, in which case in_pcbfree() may be deferred.
* in_pcbfree(). However, with TCP the inpcb may significantly outlive the
* socket, in which case in_pcbfree() is deferred.
*/
void
in_pcbdetach(struct inpcb *inp)
@ -892,15 +889,17 @@ in_pcbdetach(struct inpcb *inp)
}
/*
* in_pcbfree() is responsible for freeing an already-detached inpcb, as well
* as removing it from any global inpcb lists it might be on.
* in_pcbfree_internal() frees an inpcb that has been detached from its
* socket, and whose reference count has reached 0. It will also remove the
* inpcb from any global lists it might remain on.
*/
void
in_pcbfree(struct inpcb *inp)
static void
in_pcbfree_internal(struct inpcb *inp)
{
struct inpcbinfo *ipi = inp->inp_pcbinfo;
KASSERT(inp->inp_socket == NULL, ("%s: inp_socket != NULL", __func__));
KASSERT(inp->inp_refcount == 0, ("%s: refcount !0", __func__));
INP_INFO_WLOCK_ASSERT(ipi);
INP_WLOCK_ASSERT(inp);
@ -931,6 +930,77 @@ in_pcbfree(struct inpcb *inp)
uma_zfree(ipi->ipi_zone, inp);
}
/*
* in_pcbref() bumps the reference count on an inpcb in order to maintain
* stability of an inpcb pointer despite the inpcb lock being released. This
* is used in TCP when the inpcbinfo lock needs to be acquired or upgraded,
* but where the inpcb lock is already held.
*
* While the inpcb will not be freed, releasing the inpcb lock means that the
* connection's state may change, so the caller should be careful to
* revalidate any cached state on reacquiring the lock. Drop the reference
* using in_pcbrele().
*/
void
in_pcbref(struct inpcb *inp)
{
INP_WLOCK_ASSERT(inp);
KASSERT(inp->inp_refcount > 0, ("%s: refcount 0", __func__));
inp->inp_refcount++;
}
/*
* Drop a refcount on an inpcb elevated using in_pcbref(); because a call to
* in_pcbfree() may have been made between in_pcbref() and in_pcbrele(), we
* return a flag indicating whether or not the inpcb remains valid. If it is
* valid, we return with the inpcb lock held.
*/
int
in_pcbrele(struct inpcb *inp)
{
#ifdef INVARIANTS
struct inpcbinfo *ipi = inp->inp_pcbinfo;
#endif
KASSERT(inp->inp_refcount > 0, ("%s: refcount 0", __func__));
INP_INFO_WLOCK_ASSERT(ipi);
INP_WLOCK_ASSERT(inp);
inp->inp_refcount--;
if (inp->inp_refcount > 0)
return (0);
in_pcbfree_internal(inp);
return (1);
}
/*
* Unconditionally schedule an inpcb to be freed by decrementing its
* reference count, which should occur only after the inpcb has been detached
* from its socket. If another thread holds a temporary reference (acquired
* using in_pcbref()) then the free is deferred until that reference is
* released using in_pcbrele(), but the inpcb is still unlocked.
*/
void
in_pcbfree(struct inpcb *inp)
{
#ifdef INVARIANTS
struct inpcbinfo *ipi = inp->inp_pcbinfo;
#endif
KASSERT(inp->inp_socket == NULL, ("%s: inp_socket != NULL",
__func__));
INP_INFO_WLOCK_ASSERT(ipi);
INP_WLOCK_ASSERT(inp);
if (!in_pcbrele(inp))
INP_WUNLOCK(inp);
}
/*
* in_pcbdrop() removes an inpcb from hashed lists, releasing its address and
* port reservation, and preventing it from being returned by inpcb lookups.

3
sys/netinet/in_pcb.h
View File

@ -170,6 +170,7 @@ struct inpcb {
u_char inp_ip_p; /* (c) protocol proto */
u_char inp_ip_minttl; /* (i) minimum TTL or drop */
uint32_t inp_ispare1; /* (x) connection id / queue id */
u_int inp_refcount; /* (i) refcount */
void *inp_pspare[2]; /* (x) rtentry / general use */
/* Local and foreign ports, local and foreign addr. */
@ -478,7 +479,9 @@ struct inpcb *
struct in_addr, u_int, int, struct ifnet *);
void in_pcbnotifyall(struct inpcbinfo *pcbinfo, struct in_addr,
int, struct inpcb *(*)(struct inpcb *, int));
void in_pcbref(struct inpcb *);
void in_pcbrehash(struct inpcb *);
int in_pcbrele(struct inpcb *);
void in_pcbsetsolabel(struct socket *so);
int in_getpeeraddr(struct socket *so, struct sockaddr **nam);
int in_getsockaddr(struct socket *so, struct sockaddr **nam);