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timecounter: Lock the timecounter list

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Timecounter registration is dynamic, i.e., there is no requirement that
timecounters must be registered during single-threaded boot.  Loadable
drivers may in principle register timecounters (which can be switched to
automatically).  Timecounters cannot be unregistered, though this could
be implemented.

Registered timecounters belong to a global linked list.  Add a mutex to
synchronize insertions and the traversals done by (mpsafe) sysctl
handlers.  No functional change intended.

Reviewed by:	imp, kib
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32511
This commit is contained in:
Mark Johnston 2021-10-16 09:46:55 -04:00
parent 06ebadc5f5
commit 621fd9dcb2
1 changed files with 30 additions and 10 deletions
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40
sys/kern/kern_tc.c
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@ -97,6 +97,10 @@ static struct timehands *volatile timehands = &ths[0];
struct timecounter *timecounter = &dummy_timecounter;
static struct timecounter *timecounters = &dummy_timecounter;
/* Mutex to protect the timecounter list. */
static struct mtx tc_lock;
MTX_SYSINIT(tc_lock, &tc_lock, "tc", MTX_DEF);
int tc_min_ticktock_freq = 1;
volatile time_t time_second = 1;
@ -1188,8 +1192,6 @@ tc_init(struct timecounter *tc)
tc->tc_quality);
}
tc->tc_next = timecounters;
timecounters = tc;
/*
* Set up sysctl tree for this counter.
*/
@ -1211,6 +1213,11 @@ tc_init(struct timecounter *tc)
SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
"quality", CTLFLAG_RD, &(tc->tc_quality), 0,
"goodness of time counter");
mtx_lock(&tc_lock);
tc->tc_next = timecounters;
timecounters = tc;
/*
* Do not automatically switch if the current tc was specifically
* chosen. Never automatically use a timecounter with negative quality.
@ -1218,22 +1225,24 @@ tc_init(struct timecounter *tc)
* worse since this timecounter may not be monotonic.
*/
if (tc_chosen)
return;
goto unlock;
if (tc->tc_quality < 0)
return;
goto unlock;
if (tc_from_tunable[0] != '\0' &&
strcmp(tc->tc_name, tc_from_tunable) == 0) {
tc_chosen = 1;
tc_from_tunable[0] = '\0';
} else {
if (tc->tc_quality < timecounter->tc_quality)
return;
goto unlock;
if (tc->tc_quality == timecounter->tc_quality &&
tc->tc_frequency < timecounter->tc_frequency)
return;
goto unlock;
}
(void)tc->tc_get_timecount(tc);
timecounter = tc;
unlock:
mtx_unlock(&tc_lock);
}
/* Report the frequency of the current timecounter. */
@ -1479,16 +1488,22 @@ sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS)
struct timecounter *newtc, *tc;
int error;
mtx_lock(&tc_lock);
tc = timecounter;
strlcpy(newname, tc->tc_name, sizeof(newname));
mtx_unlock(&tc_lock);
error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req);
if (error != 0 || req->newptr == NULL)
return (error);
mtx_lock(&tc_lock);
/* Record that the tc in use now was specifically chosen. */
tc_chosen = 1;
if (strcmp(newname, tc->tc_name) == 0)
if (strcmp(newname, tc->tc_name) == 0) {
mtx_unlock(&tc_lock);
return (0);
}
for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) {
if (strcmp(newname, newtc->tc_name) != 0)
continue;
@ -1506,11 +1521,11 @@ sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS)
* use any locking and that it can be called in hard interrupt
* context via 'tc_windup()'.
*/
return (0);
break;
}
return (EINVAL);
mtx_unlock(&tc_lock);
return (newtc != NULL ? 0 : EINVAL);
}
SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware,
CTLTYPE_STRING | CTLFLAG_RWTUN | CTLFLAG_NOFETCH | CTLFLAG_MPSAFE, 0, 0,
sysctl_kern_timecounter_hardware, "A",
@ -1524,12 +1539,17 @@ sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS)
struct timecounter *tc;
int error;
error = sysctl_wire_old_buffer(req, 0);
if (error != 0)
return (error);
sbuf_new_for_sysctl(&sb, NULL, 0, req);
mtx_lock(&tc_lock);
for (tc = timecounters; tc != NULL; tc = tc->tc_next) {
if (tc != timecounters)
sbuf_putc(&sb, ' ');
sbuf_printf(&sb, "%s(%d)", tc->tc_name, tc->tc_quality);
}
mtx_unlock(&tc_lock);
error = sbuf_finish(&sb);
sbuf_delete(&sb);
return (error);