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Re-implement virtual console (constty).

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Protect conscallout with tty lock instead of Giant.  In addition to
Giant removal it also closes race on console unset.

Introduce additional lock to protect against concurrent console sets.

Remove consbuf free on console unset as unsafe, making impossible to
change buffer size after first allocation.  Instead increase default
buffer size from 8KB to 64KB and processing rate from 5Hz to 10-15Hz
to make the output more smooth.

MFC after:	1 month
This commit is contained in:
Alexander Motin 2021-09-03 22:18:51 -04:00
parent cd85b97e0e
commit bd6085c6ae
3 changed files with 62 additions and 71 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

105
sys/kern/kern_cons.c
View File

@ -105,8 +105,10 @@ static u_char console_pausing; /* pause after each line during probe */
static const char console_pausestr[] =
"<pause; press any key to proceed to next line or '.' to end pause mode>";
struct tty *constty; /* pointer to console "window" tty */
static struct mtx constty_mtx; /* Mutex for constty assignment. */
MTX_SYSINIT(constty_mtx, &constty_mtx, "constty_mtx", MTX_DEF);
static struct mtx cnputs_mtx; /* Mutex for cnputs(). */
static int use_cnputs_mtx = 0; /* != 0 if cnputs_mtx locking reqd. */
MTX_SYSINIT(cnputs_mtx, &cnputs_mtx, "cnputs_mtx", MTX_SPIN | MTX_NOWITNESS);
static void constty_timeout(void *arg);
@ -538,8 +540,8 @@ cnputsn(const char *p, size_t n)
size_t i;
int unlock_reqd = 0;
if (use_cnputs_mtx) {
/*
if (mtx_initialized(&cnputs_mtx)) {
/*
* NOTE: Debug prints and/or witness printouts in
* console driver clients can cause the "cnputs_mtx"
* mutex to recurse. Simply return if that happens.
@ -563,49 +565,72 @@ cnputs(const char *p)
cnputsn(p, strlen(p));
}
static int consmsgbuf_size = 8192;
SYSCTL_INT(_kern, OID_AUTO, consmsgbuf_size, CTLFLAG_RW, &consmsgbuf_size, 0,
"Console tty buffer size");
static unsigned int consmsgbuf_size = 65536;
SYSCTL_UINT(_kern, OID_AUTO, consmsgbuf_size, CTLFLAG_RWTUN, &consmsgbuf_size,
0, "Console tty buffer size");
/*
* Redirect console output to a tty.
*/
void
int
constty_set(struct tty *tp)
{
int size;
int size = consmsgbuf_size;
void *buf = NULL;
tty_assert_locked(tp);
if (constty == tp)
return (0);
if (constty != NULL)
return (EBUSY);
KASSERT(tp != NULL, ("constty_set: NULL tp"));
if (consbuf == NULL) {
size = consmsgbuf_size;
consbuf = malloc(size, M_TTYCONS, M_WAITOK);
msgbuf_init(&consmsgbuf, consbuf, size);
callout_init(&conscallout, 0);
tty_unlock(tp);
buf = malloc(size, M_TTYCONS, M_WAITOK);
tty_lock(tp);
}
mtx_lock(&constty_mtx);
if (constty != NULL) {
mtx_unlock(&constty_mtx);
free(buf, M_TTYCONS);
return (EBUSY);
}
if (consbuf == NULL) {
consbuf = buf;
msgbuf_init(&consmsgbuf, buf, size);
} else
free(buf, M_TTYCONS);
constty = tp;
constty_timeout(NULL);
mtx_unlock(&constty_mtx);
callout_init_mtx(&conscallout, tty_getlock(tp), 0);
constty_timeout(tp);
return (0);
}
/*
* Disable console redirection to a tty.
*/
void
constty_clear(void)
int
constty_clear(struct tty *tp)
{
int c;
constty = NULL;
if (consbuf == NULL)
return;
tty_assert_locked(tp);
if (constty != tp)
return (ENXIO);
callout_stop(&conscallout);
mtx_lock(&constty_mtx);
constty = NULL;
mtx_unlock(&constty_mtx);
while ((c = msgbuf_getchar(&consmsgbuf)) != -1)
cnputc(c);
free(consbuf, M_TTYCONS);
consbuf = NULL;
/* We never free consbuf because it can still be in use. */
return (0);
}
/* Times per second to check for pending console tty messages. */
static int constty_wakeups_per_second = 5;
static int constty_wakeups_per_second = 15;
SYSCTL_INT(_kern, OID_AUTO, constty_wakeups_per_second, CTLFLAG_RW,
&constty_wakeups_per_second, 0,
"Times per second to check for pending console tty messages");
@ -613,40 +638,20 @@ SYSCTL_INT(_kern, OID_AUTO, constty_wakeups_per_second, CTLFLAG_RW,
static void
constty_timeout(void *arg)
{
struct tty *tp = arg;
int c;
if (constty != NULL) {
tty_lock(constty);
while ((c = msgbuf_getchar(&consmsgbuf)) != -1) {
if (tty_putchar(constty, c) < 0) {
tty_unlock(constty);
constty = NULL;
break;
}
tty_assert_locked(tp);
while ((c = msgbuf_getchar(&consmsgbuf)) != -1) {
if (tty_putchar(tp, c) < 0) {
constty_clear(tp);
return;
}
if (constty != NULL)
tty_unlock(constty);
}
if (constty != NULL) {
callout_reset(&conscallout, hz / constty_wakeups_per_second,
constty_timeout, NULL);
} else {
/* Deallocate the constty buffer memory. */
constty_clear();
}
callout_reset_sbt(&conscallout, SBT_1S / constty_wakeups_per_second,
0, constty_timeout, tp, C_PREL(1));
}
static void
cn_drvinit(void *unused)
{
mtx_init(&cnputs_mtx, "cnputs_mtx", NULL, MTX_SPIN | MTX_NOWITNESS);
use_cnputs_mtx = 1;
}
SYSINIT(cndev, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, cn_drvinit, NULL);
/*
* Sysbeep(), if we have hardware for it
*/

24
sys/kern/tty.c
View File

@ -241,8 +241,7 @@ ttydev_leave(struct tty *tp)
tp->t_flags |= TF_OPENCLOSE;
/* Remove console TTY. */
if (constty == tp)
constty_clear();
constty_clear(tp);
/* Drain any output. */
if (!tty_gone(tp))
@ -1920,24 +1919,11 @@ tty_generic_ioctl(struct tty *tp, u_long cmd, void *data, int fflag,
error = priv_check(td, PRIV_TTY_CONSOLE);
if (error)
return (error);
/*
* XXX: constty should really need to be locked!
* XXX: allow disconnected constty's to be stolen!
*/
if (constty == tp)
return (0);
if (constty != NULL)
return (EBUSY);
tty_unlock(tp);
constty_set(tp);
tty_lock(tp);
} else if (constty == tp) {
constty_clear();
error = constty_set(tp);
} else {
error = constty_clear(tp);
}
return (0);
return (error);
case TIOCGWINSZ:
/* Obtain window size. */
*(struct winsize*)data = tp->t_winsize;

4
sys/sys/cons.h
View File

@ -139,8 +139,8 @@ void cnputc(int);
void cnputs(const char *);
void cnputsn(const char *, size_t);
int cnunavailable(void);
void constty_set(struct tty *tp);
void constty_clear(void);
int constty_set(struct tty *tp);
int constty_clear(struct tty *tp);
/* sc(4) / vt(4) coexistence shim */
#define VTY_SC 0x01