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tcp: Congestion control move to using reference counting.

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In the transport call on 12/3 Gleb asked to move the CC modules towards
using reference counting to prevent folks from unloading a module in use.
It was also agreed that Michael would do a user space utility like tcp_drop
that could be used to move all connections that are using a specific CC
to some other CC.

This is the half I committed to doing, making it so that we maintain a refcount
on a cc module every time a pcb refers to it and decrementing that every
time a pcb no longer uses a cc module. This also helps us simplify the
whole unloading process by getting rid of tcp_ccunload() which munged
through all the tcb's. Instead we mark a module as being removed and
prevent further references to it. We also make sure that if a module is
marked as being removed it cannot be made as the default and also
the opposite of that, if its a default it fails and does not mark it as being
removed.

Reviewed by: Michael Tuexen, Gleb Smirnoff
Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D33249
This commit is contained in:
Randall Stewart 2022-02-21 06:30:17 -05:00
parent 5ccf909af9
commit ea9017fb25
5 changed files with 173 additions and 182 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

200
sys/netinet/cc/cc.c
View file

@ -107,6 +107,45 @@ VNET_DEFINE(struct cc_algo *, default_cc_ptr) = NULL;
VNET_DEFINE(uint32_t, newreno_beta) = 50;
#define V_newreno_beta VNET(newreno_beta)
void
cc_refer(struct cc_algo *algo)
{
CC_LIST_LOCK_ASSERT();
refcount_acquire(&algo->cc_refcount);
}
void
cc_release(struct cc_algo *algo)
{
CC_LIST_LOCK_ASSERT();
refcount_release(&algo->cc_refcount);
}
void
cc_attach(struct tcpcb *tp, struct cc_algo *algo)
{
/*
* Attach the tcpcb to the algorithm.
*/
CC_LIST_RLOCK();
CC_ALGO(tp) = algo;
cc_refer(algo);
CC_LIST_RUNLOCK();
}
void
cc_detach(struct tcpcb *tp)
{
struct cc_algo *algo;
CC_LIST_RLOCK();
algo = CC_ALGO(tp);
CC_ALGO(tp) = NULL;
cc_release(algo);
CC_LIST_RUNLOCK();
}
/*
* Sysctl handler to show and change the default CC algorithm.
*/
@ -137,6 +176,10 @@ cc_default_algo(SYSCTL_HANDLER_ARGS)
STAILQ_FOREACH(funcs, &cc_list, entries) {
if (strncmp(default_cc, funcs->name, sizeof(default_cc)))
continue;
if (funcs->flags & CC_MODULE_BEING_REMOVED) {
/* Its being removed, its not eligible */
continue;
}
V_default_cc_ptr = funcs;
error = 0;
break;
@ -153,12 +196,12 @@ static int
cc_list_available(SYSCTL_HANDLER_ARGS)
{
struct cc_algo *algo;
struct sbuf *s;
int err, first, nalgos;
err = nalgos = 0;
first = 1;
int error, nalgos;
int linesz;
char *buffer, *cp;
size_t bufsz, outsz;
error = nalgos = 0;
CC_LIST_RLOCK();
STAILQ_FOREACH(algo, &cc_list, entries) {
nalgos++;
@ -167,37 +210,34 @@ cc_list_available(SYSCTL_HANDLER_ARGS)
if (nalgos == 0) {
return (ENOENT);
}
s = sbuf_new(NULL, NULL, nalgos * TCP_CA_NAME_MAX, SBUF_FIXEDLEN);
bufsz = (nalgos+2) * ((TCP_CA_NAME_MAX + 13) + 1);
buffer = malloc(bufsz, M_TEMP, M_WAITOK);
cp = buffer;
if (s == NULL)
return (ENOMEM);
/*
* It is theoretically possible for the CC list to have grown in size
* since the call to sbuf_new() and therefore for the sbuf to be too
* small. If this were to happen (incredibly unlikely), the sbuf will
* reach an overflow condition, sbuf_printf() will return an error and
* the sysctl will fail gracefully.
*/
linesz = snprintf(cp, bufsz, "\n%-16s%c %s\n", "CCmod", 'D',
"PCB count");
cp += linesz;
bufsz -= linesz;
outsz = linesz;
CC_LIST_RLOCK();
STAILQ_FOREACH(algo, &cc_list, entries) {
err = sbuf_printf(s, first ? "%s" : ", %s", algo->name);
if (err) {
/* Sbuf overflow condition. */
err = EOVERFLOW;
linesz = snprintf(cp, bufsz, "%-16s%c %u\n",
algo->name,
(algo == CC_DEFAULT_ALGO()) ? '*' : ' ',
algo->cc_refcount);
if (linesz >= bufsz) {
error = EOVERFLOW;
break;
}
first = 0;
cp += linesz;
bufsz -= linesz;
outsz += linesz;
}
CC_LIST_RUNLOCK();
if (!err) {
sbuf_finish(s);
err = sysctl_handle_string(oidp, sbuf_data(s), 0, req);
}
sbuf_delete(s);
return (err);
if (error == 0)
error = sysctl_handle_string(oidp, buffer, outsz + 1, req);
free(buffer, M_TEMP);
return (error);
}
/*
@ -243,41 +283,36 @@ cc_init(void)
int
cc_deregister_algo(struct cc_algo *remove_cc)
{
struct cc_algo *funcs, *tmpfuncs;
int err;
err = ENOENT;
struct cc_algo *funcs;
int found = 0;
/* Remove algo from cc_list so that new connections can't use it. */
CC_LIST_WLOCK();
STAILQ_FOREACH_SAFE(funcs, &cc_list, entries, tmpfuncs) {
if (funcs == remove_cc) {
if (cc_check_default(remove_cc)) {
CC_LIST_WUNLOCK();
return(EBUSY);
}
break;
}
/* This is unlikely to fail */
STAILQ_FOREACH(funcs, &cc_list, entries) {
if (funcs == remove_cc)
found = 1;
}
remove_cc->flags |= CC_MODULE_BEING_REMOVED;
CC_LIST_WUNLOCK();
err = tcp_ccalgounload(remove_cc);
/*
* Now back through and we either remove the temp flag
* or pull the registration.
*/
CC_LIST_WLOCK();
STAILQ_FOREACH_SAFE(funcs, &cc_list, entries, tmpfuncs) {
if (funcs == remove_cc) {
if (err == 0)
STAILQ_REMOVE(&cc_list, funcs, cc_algo, entries);
else
funcs->flags &= ~CC_MODULE_BEING_REMOVED;
break;
}
if (found == 0) {
/* Nothing to remove? */
CC_LIST_WUNLOCK();
return (ENOENT);
}
/* We assert it should have been MOD_QUIESCE'd */
KASSERT((remove_cc->flags & CC_MODULE_BEING_REMOVED),
("remove_cc:%p does not have CC_MODULE_BEING_REMOVED flag", remove_cc));
if (cc_check_default(remove_cc)) {
CC_LIST_WUNLOCK();
return(EBUSY);
}
if (remove_cc->cc_refcount != 0) {
CC_LIST_WUNLOCK();
return (EBUSY);
}
STAILQ_REMOVE(&cc_list, remove_cc, cc_algo, entries);
CC_LIST_WUNLOCK();
return (err);
return (0);
}
/*
@ -304,6 +339,9 @@ cc_register_algo(struct cc_algo *add_cc)
break;
}
}
/* Init its reference count */
if (err == 0)
refcount_init(&add_cc->cc_refcount, 0);
/*
* The first loaded congestion control module will become
* the default until we find the "CC_DEFAULT" defined in
@ -526,6 +564,20 @@ newreno_cc_ack_received(struct cc_var *ccv, uint16_t type)
}
}
static int
cc_stop_new_assignments(struct cc_algo *algo)
{
CC_LIST_WLOCK();
if (cc_check_default(algo)) {
/* A default cannot be removed */
CC_LIST_WUNLOCK();
return (EBUSY);
}
algo->flags |= CC_MODULE_BEING_REMOVED;
CC_LIST_WUNLOCK();
return (0);
}
/*
* Handles kld related events. Returns 0 on success, non-zero on failure.
*/
@ -555,16 +607,32 @@ cc_modevent(module_t mod, int event_type, void *data)
err = cc_register_algo(algo);
break;
case MOD_QUIESCE:
case MOD_SHUTDOWN:
case MOD_UNLOAD:
err = cc_deregister_algo(algo);
if (!err && algo->mod_destroy != NULL)
algo->mod_destroy();
if (err == ENOENT)
err = 0;
break;
case MOD_QUIESCE:
/* Stop any new assigments */
err = cc_stop_new_assignments(algo);
break;
case MOD_UNLOAD:
/*
* Deregister and remove the module from the list
*/
CC_LIST_WLOCK();
/* Even with -f we can't unload if its the default */
if (cc_check_default(algo)) {
/* A default cannot be removed */
CC_LIST_WUNLOCK();
return (EBUSY);
}
/*
* If -f was used and users are still attached to
* the algorithm things are going to go boom.
*/
err = cc_deregister_algo(algo);
if ((err == 0) && (algo->mod_destroy != NULL)) {
algo->mod_destroy();
}
break;
default:
err = EINVAL;
break;

11
sys/netinet/cc/cc.h
View file

@ -200,6 +200,7 @@ struct cc_algo {
int (*ctl_output)(struct cc_var *, struct sockopt *, void *);
STAILQ_ENTRY (cc_algo) entries;
u_int cc_refcount;
uint8_t flags;
};
@ -236,5 +237,15 @@ void newreno_cc_after_idle(struct cc_var *);
void newreno_cc_cong_signal(struct cc_var *, uint32_t );
void newreno_cc_ack_received(struct cc_var *, uint16_t);
/* Called to temporarily keep an algo from going away during change */
void cc_refer(struct cc_algo *algo);
/* Called to release the temporary hold */
void cc_release(struct cc_algo *algo);
/* Called to attach a CC algorithm to a tcpcb */
void cc_attach(struct tcpcb *, struct cc_algo *);
/* Called to detach a CC algorithm from a tcpcb */
void cc_detach(struct tcpcb *);
#endif /* _KERNEL */
#endif /* _NETINET_CC_CC_H_ */

95
sys/netinet/tcp_subr.c
View file

@ -2171,10 +2171,7 @@ tcp_newtcpcb(struct inpcb *inp)
/*
* Use the current system default CC algorithm.
*/
CC_LIST_RLOCK();
KASSERT(!STAILQ_EMPTY(&cc_list), ("cc_list is empty!"));
CC_ALGO(tp) = CC_DEFAULT_ALGO();
CC_LIST_RUNLOCK();
cc_attach(tp, CC_DEFAULT_ALGO());
/*
* The tcpcb will hold a reference on its inpcb until tcp_discardcb()
@ -2185,6 +2182,7 @@ tcp_newtcpcb(struct inpcb *inp)
if (CC_ALGO(tp)->cb_init != NULL)
if (CC_ALGO(tp)->cb_init(tp->ccv, NULL) > 0) {
cc_detach(tp);
if (tp->t_fb->tfb_tcp_fb_fini)
(*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
in_pcbrele_wlocked(inp);
@ -2276,93 +2274,6 @@ tcp_newtcpcb(struct inpcb *inp)
return (tp); /* XXX */
}
/*
* Switch the congestion control algorithm back to Vnet default for any active
* control blocks using an algorithm which is about to go away. If the algorithm
* has a cb_init function and it fails (no memory) then the operation fails and
* the unload will not succeed.
*
*/
int
tcp_ccalgounload(struct cc_algo *unload_algo)
{
struct cc_algo *oldalgo, *newalgo;
struct inpcb *inp;
struct tcpcb *tp;
VNET_ITERATOR_DECL(vnet_iter);
/*
* Check all active control blocks across all network stacks and change
* any that are using "unload_algo" back to its default. If "unload_algo"
* requires cleanup code to be run, call it.
*/
VNET_LIST_RLOCK();
VNET_FOREACH(vnet_iter) {
CURVNET_SET(vnet_iter);
struct inpcb_iterator inpi = INP_ALL_ITERATOR(&V_tcbinfo,
INPLOOKUP_WLOCKPCB);
/*
* XXXGL: would new accept(2)d connections use algo being
* unloaded?
*/
newalgo = CC_DEFAULT_ALGO();
while ((inp = inp_next(&inpi)) != NULL) {
/* Important to skip tcptw structs. */
if (!(inp->inp_flags & INP_TIMEWAIT) &&
(tp = intotcpcb(inp)) != NULL) {
/*
* By holding INP_WLOCK here, we are assured
* that the connection is not currently
* executing inside the CC module's functions.
* We attempt to switch to the Vnets default,
* if the init fails then we fail the whole
* operation and the module unload will fail.
*/
if (CC_ALGO(tp) == unload_algo) {
struct cc_var cc_mem;
int err;
oldalgo = CC_ALGO(tp);
memset(&cc_mem, 0, sizeof(cc_mem));
cc_mem.ccvc.tcp = tp;
if (newalgo->cb_init == NULL) {
/*
* No init we can skip the
* dance around a possible failure.
*/
CC_DATA(tp) = NULL;
goto proceed;
}
err = (newalgo->cb_init)(&cc_mem, NULL);
if (err) {
/*
* Presumably no memory the caller will
* need to try again.
*/
INP_WUNLOCK(inp);
CURVNET_RESTORE();
VNET_LIST_RUNLOCK();
return (err);
}
proceed:
if (oldalgo->cb_destroy != NULL)
oldalgo->cb_destroy(tp->ccv);
CC_ALGO(tp) = newalgo;
memcpy(tp->ccv, &cc_mem, sizeof(struct cc_var));
if (TCPS_HAVEESTABLISHED(tp->t_state) &&
(CC_ALGO(tp)->conn_init != NULL)) {
/* Yep run the connection init for the new CC */
CC_ALGO(tp)->conn_init(tp->ccv);
}
}
}
}
CURVNET_RESTORE();
}
VNET_LIST_RUNLOCK();
return (0);
}
/*
* Drop a TCP connection, reporting
* the specified error. If connection is synchronized,
@ -2443,6 +2354,8 @@ tcp_discardcb(struct tcpcb *tp)
if (CC_ALGO(tp)->cb_destroy != NULL)
CC_ALGO(tp)->cb_destroy(tp->ccv);
CC_DATA(tp) = NULL;
/* Detach from the CC algorithm */
cc_detach(tp);
#ifdef TCP_HHOOK
khelp_destroy_osd(tp->osd);

48
sys/netinet/tcp_usrreq.c
View file

@ -2004,7 +2004,7 @@ copyin_tls_enable(struct sockopt *sopt, struct tls_enable *tls)
extern struct cc_algo newreno_cc_algo;
static int
tcp_congestion(struct inpcb *inp, struct sockopt *sopt)
tcp_set_cc_mod(struct inpcb *inp, struct sockopt *sopt)
{
struct cc_algo *algo;
void *ptr = NULL;
@ -2020,7 +2020,7 @@ tcp_congestion(struct inpcb *inp, struct sockopt *sopt)
return(error);
buf[sopt->sopt_valsize] = '\0';
CC_LIST_RLOCK();
STAILQ_FOREACH(algo, &cc_list, entries)
STAILQ_FOREACH(algo, &cc_list, entries) {
if (strncmp(buf, algo->name,
TCP_CA_NAME_MAX) == 0) {
if (algo->flags & CC_MODULE_BEING_REMOVED) {
@ -2029,30 +2029,24 @@ tcp_congestion(struct inpcb *inp, struct sockopt *sopt)
}
break;
}
}
if (algo == NULL) {
CC_LIST_RUNLOCK();
return(ESRCH);
}
do_over:
/*
* With a reference the algorithm cannot be removed
* so we hold a reference through the change process.
*/
cc_refer(algo);
CC_LIST_RUNLOCK();
if (algo->cb_init != NULL) {
/* We can now pre-get the memory for the CC */
mem_sz = (*algo->cc_data_sz)();
if (mem_sz == 0) {
goto no_mem_needed;
}
CC_LIST_RUNLOCK();
ptr = malloc(mem_sz, M_CC_MEM, M_WAITOK);
CC_LIST_RLOCK();
STAILQ_FOREACH(algo, &cc_list, entries)
if (strncmp(buf, algo->name,
TCP_CA_NAME_MAX) == 0)
break;
if (algo == NULL) {
if (ptr)
free(ptr, M_CC_MEM);
CC_LIST_RUNLOCK();
return(ESRCH);
}
} else {
no_mem_needed:
mem_sz = 0;
@ -2063,22 +2057,20 @@ no_mem_needed:
* back the inplock.
*/
memset(&cc_mem, 0, sizeof(cc_mem));
if (mem_sz != (*algo->cc_data_sz)()) {
if (ptr)
free(ptr, M_CC_MEM);
goto do_over;
}
INP_WLOCK(inp);
if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
INP_WUNLOCK(inp);
if (ptr)
free(ptr, M_CC_MEM);
/* Release our temp reference */
CC_LIST_RLOCK();
cc_release(algo);
CC_LIST_RUNLOCK();
free(ptr, M_CC_MEM);
return (ECONNRESET);
}
tp = intotcpcb(inp);
if (ptr != NULL)
memset(ptr, 0, mem_sz);
CC_LIST_RUNLOCK();
cc_mem.ccvc.tcp = tp;
/*
* We once again hold a write lock over the tcb so it's
@ -2103,8 +2095,12 @@ no_mem_needed:
*/
if (CC_ALGO(tp)->cb_destroy != NULL)
CC_ALGO(tp)->cb_destroy(tp->ccv);
/* Detach the old CC from the tcpcb */
cc_detach(tp);
/* Copy in our temp memory that was inited */
memcpy(tp->ccv, &cc_mem, sizeof(struct cc_var));
tp->cc_algo = algo;
/* Now attach the new, which takes a reference */
cc_attach(tp, algo);
/* Ok now are we where we have gotten past any conn_init? */
if (TCPS_HAVEESTABLISHED(tp->t_state) && (CC_ALGO(tp)->conn_init != NULL)) {
/* Yep run the connection init for the new CC */
@ -2113,6 +2109,10 @@ no_mem_needed:
} else if (ptr)
free(ptr, M_CC_MEM);
INP_WUNLOCK(inp);
/* Now lets release our temp reference */
CC_LIST_RLOCK();
cc_release(algo);
CC_LIST_RUNLOCK();
return (error);
}
@ -2336,7 +2336,7 @@ unlock_and_done:
break;
case TCP_CONGESTION:
error = tcp_congestion(inp, sopt);
error = tcp_set_cc_mod(inp, sopt);
break;
case TCP_REUSPORT_LB_NUMA:

1
sys/netinet/tcp_var.h
View file

@ -1076,7 +1076,6 @@ VNET_DECLARE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST + 1]);
#endif
int tcp_addoptions(struct tcpopt *, u_char *);
int tcp_ccalgounload(struct cc_algo *unload_algo);
struct tcpcb *
tcp_close(struct tcpcb *);
void tcp_discardcb(struct tcpcb *);