Author: markj
Date: Fri Sep 20 23:50:14 2013
New Revision: 255749
URL: http://svnweb.freebsd.org/changeset/base/255749
Log:
MFC r250953:
The fasttrap provider cleans up probes asynchronously when a process with
USDT probes exits. This was previously done with a callout; however, it is
possible to sleep while holding the DTrace mutexes, so a panic will occur
on INVARIANTS kernels if the callout handler can't immediately acquire one
of these mutexes. This panic will be frequently triggered on systems where
a USDT-enabled program (perl, for instance) is often run.
This revision changes the fasttrap cleanup mechanism so that a dedicated
thread is used instead of a callout. The old behaviour is otherwise
preserved.
MFC r252493:
Be sure to destory the fasttrap cleanup mutex when unloading the fasttrap
module. This should be MFCed with r250953.
Modified:
stable/9/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
Directory Properties:
stable/9/sys/ (props changed)
stable/9/sys/cddl/contrib/opensolaris/ (props changed)
Modified: stable/9/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
==============================================================================
--- stable/9/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c Fri Sep
20 23:22:00 2013 (r255748)
+++ stable/9/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c Fri Sep
20 23:50:14 2013 (r255749)
@@ -155,9 +155,9 @@ static struct cdevsw fasttrap_cdevsw = {
static struct cdev *fasttrap_cdev;
static dtrace_meta_provider_id_t fasttrap_meta_id;
-static struct callout fasttrap_timeout;
+static struct proc *fasttrap_cleanup_proc;
static struct mtx fasttrap_cleanup_mtx;
-static uint_t fasttrap_cleanup_work;
+static uint_t fasttrap_cleanup_work, fasttrap_cleanup_drain,
fasttrap_cleanup_cv;
/*
* Generation count on modifications to the global tracepoint lookup table.
@@ -310,8 +310,11 @@ fasttrap_mod_barrier(uint64_t gen)
}
/*
- * This is the timeout's callback for cleaning up the providers and their
- * probes.
+ * This function performs asynchronous cleanup of fasttrap providers. The
+ * Solaris implementation of this mechanism use a timeout that's activated in
+ * fasttrap_pid_cleanup(), but this doesn't work in FreeBSD: one may sleep
while
+ * holding the DTrace mutexes, but it is unsafe to sleep in a callout handler.
+ * Thus we use a dedicated process to perform the cleanup when requested.
*/
/*ARGSUSED*/
static void
@@ -322,11 +325,8 @@ fasttrap_pid_cleanup_cb(void *data)
dtrace_provider_id_t provid;
int i, later = 0, rval;
- static volatile int in = 0;
- ASSERT(in == 0);
- in = 1;
-
- while (fasttrap_cleanup_work) {
+ mtx_lock(&fasttrap_cleanup_mtx);
+ while (!fasttrap_cleanup_drain || later > 0) {
fasttrap_cleanup_work = 0;
mtx_unlock(&fasttrap_cleanup_mtx);
@@ -397,39 +397,32 @@ fasttrap_pid_cleanup_cb(void *data)
}
mutex_exit(&bucket->ftb_mtx);
}
-
mtx_lock(&fasttrap_cleanup_mtx);
- }
-#if 0
- ASSERT(fasttrap_timeout != 0);
-#endif
+ /*
+ * If we were unable to retire a provider, try again after a
+ * second. This situation can occur in certain circumstances
+ * where providers cannot be unregistered even though they have
+ * no probes enabled because of an execution of dtrace -l or
+ * something similar.
+ */
+ if (later > 0 || fasttrap_cleanup_work ||
+ fasttrap_cleanup_drain) {
+ mtx_unlock(&fasttrap_cleanup_mtx);
+ pause("ftclean", hz);
+ mtx_lock(&fasttrap_cleanup_mtx);
+ } else
+ mtx_sleep(&fasttrap_cleanup_cv, &fasttrap_cleanup_mtx,
+ 0, "ftcl", 0);
+ }
/*
- * If we were unable to remove a retired provider, try again after
- * a second. This situation can occur in certain circumstances where
- * providers cannot be unregistered even though they have no probes
- * enabled because of an execution of dtrace -l or something similar.
- * If the timeout has been disabled (set to 1 because we're trying
- * to detach), we set fasttrap_cleanup_work to ensure that we'll
- * get a chance to do that work if and when the timeout is reenabled
- * (if detach fails).
- */
- if (later > 0) {
- if (callout_active(&fasttrap_timeout)) {
- callout_reset(&fasttrap_timeout, hz,
- &fasttrap_pid_cleanup_cb, NULL);
- }
-
- else if (later > 0)
- fasttrap_cleanup_work = 1;
- } else {
-#if !defined(sun)
- /* Nothing to be done for FreeBSD */
-#endif
- }
+ * Wake up the thread in fasttrap_unload() now that we're done.
+ */
+ wakeup(&fasttrap_cleanup_drain);
+ mtx_unlock(&fasttrap_cleanup_mtx);
- in = 0;
+ kthread_exit();
}
/*
@@ -440,8 +433,10 @@ fasttrap_pid_cleanup(void)
{
mtx_lock(&fasttrap_cleanup_mtx);
- fasttrap_cleanup_work = 1;
- callout_reset(&fasttrap_timeout, 1, &fasttrap_pid_cleanup_cb, NULL);
+ if (!fasttrap_cleanup_work) {
+ fasttrap_cleanup_work = 1;
+ wakeup(&fasttrap_cleanup_cv);
+ }
mtx_unlock(&fasttrap_cleanup_mtx);
}
@@ -991,7 +986,6 @@ fasttrap_pid_enable(void *arg, dtrace_id
proc_t *p = NULL;
int i, rc;
-
ASSERT(probe != NULL);
ASSERT(!probe->ftp_enabled);
ASSERT(id == probe->ftp_id);
@@ -2272,17 +2266,23 @@ static int
fasttrap_load(void)
{
ulong_t nent;
- int i;
+ int i, ret;
/* Create the /dev/dtrace/fasttrap entry. */
fasttrap_cdev = make_dev(&fasttrap_cdevsw, 0, UID_ROOT, GID_WHEEL,
0600,
"dtrace/fasttrap");
mtx_init(&fasttrap_cleanup_mtx, "fasttrap clean", "dtrace", MTX_DEF);
- callout_init_mtx(&fasttrap_timeout, &fasttrap_cleanup_mtx, 0);
mutex_init(&fasttrap_count_mtx, "fasttrap count mtx", MUTEX_DEFAULT,
NULL);
+ ret = kproc_create(fasttrap_pid_cleanup_cb, NULL,
+ &fasttrap_cleanup_proc, 0, 0, "ftcleanup");
+ if (ret != 0) {
+ destroy_dev(fasttrap_cdev);
+ return (ret);
+ }
+
#if defined(sun)
fasttrap_max = ddi_getprop(DDI_DEV_T_ANY, devi, DDI_PROP_DONTPASS,
"fasttrap-max-probes", FASTTRAP_MAX_DEFAULT);
@@ -2389,15 +2389,6 @@ fasttrap_unload(void)
return (-1);
/*
- * Prevent any new timeouts from running by setting fasttrap_timeout
- * to a non-zero value, and wait for the current timeout to complete.
- */
- mtx_lock(&fasttrap_cleanup_mtx);
- fasttrap_cleanup_work = 0;
- callout_drain(&fasttrap_timeout);
- mtx_unlock(&fasttrap_cleanup_mtx);
-
- /*
* Iterate over all of our providers. If there's still a process
* that corresponds to that pid, fail to detach.
*/
@@ -2431,26 +2422,21 @@ fasttrap_unload(void)
}
if (fail) {
- uint_t work;
- /*
- * If we're failing to detach, we need to unblock timeouts
- * and start a new timeout if any work has accumulated while
- * we've been unsuccessfully trying to detach.
- */
- mtx_lock(&fasttrap_cleanup_mtx);
- work = fasttrap_cleanup_work;
- callout_drain(&fasttrap_timeout);
- mtx_unlock(&fasttrap_cleanup_mtx);
-
- if (work)
- fasttrap_pid_cleanup();
-
(void) dtrace_meta_register("fasttrap", &fasttrap_mops, NULL,
&fasttrap_meta_id);
return (-1);
}
+ mtx_lock(&fasttrap_cleanup_mtx);
+ fasttrap_cleanup_drain = 1;
+ /* Wait for the cleanup thread to finish up and signal us. */
+ wakeup(&fasttrap_cleanup_cv);
+ mtx_sleep(&fasttrap_cleanup_drain, &fasttrap_cleanup_mtx, 0, "ftcld",
+ 0);
+ fasttrap_cleanup_proc = NULL;
+ mtx_destroy(&fasttrap_cleanup_mtx);
+
#ifdef DEBUG
mutex_enter(&fasttrap_count_mtx);
ASSERT(fasttrap_pid_count == 0);
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