fasttrap.c

Sun Solaris 10 中的 DTrace 组件的源代码。请参看: http://www.sun.com/software/solaris/observability.jsp

	 * Tracepoints whose provider is now defunct are also considered
	 * defunct.
	 */
again:
	mutex_enter(&bucket->ftb_mtx);
	for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
		if (tp->ftt_pid != pid || tp->ftt_pc != pc ||
		    tp->ftt_prov->ftp_defunct)
			continue;

		/*
		 * Now that we've found a matching tracepoint, it would be
		 * a decent idea to confirm that the tracepoint is still
		 * enabled and the trap instruction hasn't been overwritten.
		 * Since this is a little hairy, we'll punt for now.
		 */

		/*
		 * This can't be the first interested probe. We don't have
		 * to worry about another thread being in the midst of
		 * deleting this tracepoint (which would be the only valid
		 * reason for a tracepoint to have no interested probes)
		 * since we're holding P_PR_LOCK for this process.
		 */
		ASSERT(tp->ftt_ids != NULL || tp->ftt_retids != NULL);

		if (probe->ftp_type == DTFTP_RETURN ||
		    probe->ftp_type == DTFTP_POST_OFFSETS) {
			id->fti_next = tp->ftt_retids;
			membar_producer();
			tp->ftt_retids = id;
			membar_producer();
		} else {
			id->fti_next = tp->ftt_ids;
			membar_producer();
			tp->ftt_ids = id;
			membar_producer();
		}

		mutex_exit(&bucket->ftb_mtx);

		if (new_tp != NULL) {
			new_tp->ftt_ids = NULL;
			new_tp->ftt_retids = NULL;
		}

		return (0);
	}

	/*
	 * If we have a good tracepoint ready to go, install it now while
	 * we have the lock held and no one can screw with us.
	 */
	if (new_tp != NULL) {
		int rc;

		new_tp->ftt_next = bucket->ftb_data;
		membar_producer();
		bucket->ftb_data = new_tp;
		membar_producer();
		mutex_exit(&bucket->ftb_mtx);

		/*
		 * Activate the tracepoint in the isa-specific manner.
		 */
		if (fasttrap_tracepoint_install(p, new_tp) != 0) {
			rc = 1;
		} else {
			/*
			 * Increment the count of the number of tracepoints
			 * active in the victim process.
			 */
			ASSERT(p->p_proc_flag & P_PR_LOCK);
			p->p_dtrace_count++;
			rc = 0;
		}

		return (rc);
	}

	mutex_exit(&bucket->ftb_mtx);

	/*
	 * Initialize the tracepoint that's been preallocated with the probe.
	 */
	new_tp = probe->ftp_tps[index].fit_tp;

	ASSERT(new_tp->ftt_pid == pid);
	ASSERT(new_tp->ftt_pc == pc);
	ASSERT(new_tp->ftt_prov == probe->ftp_prov);
	ASSERT(new_tp->ftt_ids == NULL);
	ASSERT(new_tp->ftt_retids == NULL);

	if (probe->ftp_type == DTFTP_RETURN ||
	    probe->ftp_type == DTFTP_POST_OFFSETS) {
		id->fti_next = NULL;
		new_tp->ftt_retids = id;
	} else {
		id->fti_next = NULL;
		new_tp->ftt_ids = id;
	}

	/*
	 * If the isa-dependent initialization goes to plan, go back to the
	 * beginning and try to install this freshly made tracepoint.
	 */
	if (fasttrap_tracepoint_init(p, probe, new_tp, pc) == 0)
		goto again;

	new_tp->ftt_ids = NULL;
	new_tp->ftt_retids = NULL;

	return (1);
}

static void
fasttrap_tracepoint_disable(proc_t *p, fasttrap_probe_t *probe, uint_t index)
{
	fasttrap_bucket_t *bucket;
	fasttrap_provider_t *provider = probe->ftp_prov;
	fasttrap_tracepoint_t **pp, *tp;
	fasttrap_id_t *id, **idp;
	pid_t pid;
	uintptr_t pc;

	ASSERT(index < probe->ftp_ntps);

	pid = probe->ftp_pid;
	pc = probe->ftp_tps[index].fit_tp->ftt_pc;

	ASSERT(probe->ftp_tps[index].fit_tp->ftt_pid == pid);

	/*
	 * Find the tracepoint and make sure that our id is one of the
	 * ones registered with it.
	 */
	bucket = &fasttrap_tpoints.fth_table[FASTTRAP_TPOINTS_INDEX(pid, pc)];
	mutex_enter(&bucket->ftb_mtx);
	for (tp = bucket->ftb_data; tp != NULL; tp = tp->ftt_next) {
		if (tp->ftt_pid == pid && tp->ftt_pc == pc &&
		    tp->ftt_prov == provider)
			break;
	}

	/*
	 * If we somehow lost this tracepoint, we're in a world of hurt.
	 */
	ASSERT(tp != NULL);

	if (probe->ftp_type == DTFTP_RETURN ||
	    probe->ftp_type == DTFTP_POST_OFFSETS) {
		ASSERT(tp->ftt_retids != NULL);
		idp = &tp->ftt_retids;
	} else {
		ASSERT(tp->ftt_ids != NULL);
		idp = &tp->ftt_ids;
	}

	while ((*idp)->fti_probe != probe) {
		idp = &(*idp)->fti_next;
		ASSERT(*idp != NULL);
	}

	id = *idp;
	*idp = id->fti_next;
	membar_producer();

	ASSERT(id->fti_probe == probe);

	/*
	 * If there are other registered enablings of this tracepoint, we're
	 * all done, but if this was the last probe assocated with this
	 * this tracepoint, we need to remove and free it.
	 */
	if (tp->ftt_ids != NULL || tp->ftt_retids != NULL) {

		/*
		 * If the current probe's tracepoint is in use, swap it
		 * for an unused tracepoint.
		 */
		if (tp == probe->ftp_tps[index].fit_tp) {
			fasttrap_probe_t *tmp_probe;
			fasttrap_tracepoint_t **tmp_tp;
			uint_t tmp_index;

			if (tp->ftt_ids != NULL) {
				tmp_probe = tp->ftt_ids->fti_probe;
				tmp_index = FASTTRAP_ID_INDEX(tp->ftt_ids);
				tmp_tp = &tmp_probe->ftp_tps[tmp_index].fit_tp;
			} else {
				tmp_probe = tp->ftt_retids->fti_probe;
				tmp_index = FASTTRAP_ID_INDEX(tp->ftt_retids);
				tmp_tp = &tmp_probe->ftp_tps[tmp_index].fit_tp;
			}

			ASSERT(*tmp_tp != NULL);
			ASSERT(*tmp_tp != probe->ftp_tps[index].fit_tp);
			ASSERT((*tmp_tp)->ftt_ids == NULL);
			ASSERT((*tmp_tp)->ftt_retids == NULL);

			probe->ftp_tps[index].fit_tp = *tmp_tp;
			*tmp_tp = tp;

		}

		mutex_exit(&bucket->ftb_mtx);

		/*
		 * Tag the modified probe with the generation in which it was
		 * changed.
		 */
		probe->ftp_gen = fasttrap_mod_gen;
		return;
	}

	mutex_exit(&bucket->ftb_mtx);

	/*
	 * We can't safely remove the tracepoint from the set of active
	 * tracepoints until we've actually removed the fasttrap instruction
	 * from the process's text. We can, however, operate on this
	 * tracepoint secure in the knowledge that no other thread is going to
	 * be looking at it since we hold P_PR_LOCK on the process if it's
	 * live or we hold the provider lock on the process if it's dead and
	 * gone.
	 */

	/*
	 * We only need to remove the actual instruction if we're looking
	 * at an existing process
	 */
	if (p != NULL) {
		/*
		 * If we fail to restore the instruction we need to kill
		 * this process since it's in a completely unrecoverable
		 * state.
		 */
		if (fasttrap_tracepoint_remove(p, tp) != 0)
			fasttrap_sigtrap(p, NULL, pc);

		/*
		 * Decrement the count of the number of tracepoints active
		 * in the victim process.
		 */
		ASSERT(p->p_proc_flag & P_PR_LOCK);
		p->p_dtrace_count--;
	}

	/*
	 * Remove the probe from the hash table of active tracepoints.
	 */
	mutex_enter(&bucket->ftb_mtx);
	pp = (fasttrap_tracepoint_t **)&bucket->ftb_data;
	ASSERT(*pp != NULL);
	while (*pp != tp) {
		pp = &(*pp)->ftt_next;
		ASSERT(*pp != NULL);
	}

	*pp = tp->ftt_next;
	membar_producer();

	mutex_exit(&bucket->ftb_mtx);

	/*
	 * Tag the modified probe with the generation in which it was changed.
	 */
	probe->ftp_gen = fasttrap_mod_gen;
}

typedef int fasttrap_probe_f(struct regs *);

static void
fasttrap_enable_common(int *count, fasttrap_probe_f **fptr, fasttrap_probe_f *f,
    fasttrap_probe_f **fptr2, fasttrap_probe_f *f2)
{
	/*
	 * We don't have to play the rw lock game here because we're
	 * providing something rather than taking something away --
	 * we can be sure that no threads have tried to follow this
	 * function pointer yet.
	 */
	mutex_enter(&fasttrap_count_mtx);
	if (*count == 0) {
		ASSERT(*fptr == NULL);
		*fptr = f;
		if (fptr2 != NULL)
			*fptr2 = f2;
	}
	ASSERT(*fptr == f);
	ASSERT(fptr2 == NULL || *fptr2 == f2);
	(*count)++;
	mutex_exit(&fasttrap_count_mtx);
}

static void
fasttrap_disable_common(int *count, fasttrap_probe_f **fptr,
    fasttrap_probe_f **fptr2)
{
	ASSERT(MUTEX_HELD(&cpu_lock));

	mutex_enter(&fasttrap_count_mtx);
	(*count)--;
	ASSERT(*count >= 0);
	if (*count == 0) {
		cpu_t *cur, *cpu = CPU;

		for (cur = cpu->cpu_next_onln; cur != cpu;
			cur = cur->cpu_next_onln) {
			rw_enter(&cur->cpu_ft_lock, RW_WRITER);
		}

		*fptr = NULL;
		if (fptr2 != NULL)
			*fptr2 = NULL;

		for (cur = cpu->cpu_next_onln; cur != cpu;
			cur = cur->cpu_next_onln) {
			rw_exit(&cur->cpu_ft_lock);
		}
	}
	mutex_exit(&fasttrap_count_mtx);
}

/*ARGSUSED*/
static void
fasttrap_enable(void *arg, dtrace_id_t id, void *parg)
{
	/*
	 * Enable the probe that corresponds to statically placed trace
	 * points which have not explicitly been placed in the process's text
	 * by the fasttrap provider.
	 */
	ASSERT(arg == NULL);
	ASSERT(id == fasttrap_probe_id);

	fasttrap_enable_common(&fasttrap_count,
	    &dtrace_fasttrap_probe_ptr, fasttrap_probe, NULL, NULL);
}


/*ARGSUSED*/
static void
fasttrap_pid_enable(void *arg, dtrace_id_t id, void *parg)
{
	fasttrap_probe_t *probe = parg;
	proc_t *p;
	int i;

	ASSERT(probe != NULL);
	ASSERT(!probe->ftp_enabled);
	ASSERT(id == probe->ftp_id);
	ASSERT(MUTEX_HELD(&cpu_lock));

	/*
	 * Increment the count of enabled probes on this probe's provider;
	 * the provider can't go away while the probe still exists. We
	 * must increment this even if we aren't able to properly enable
	 * this probe.
	 */
	mutex_enter(&probe->ftp_prov->ftp_mtx);
	probe->ftp_prov->ftp_rcount++;
	mutex_exit(&probe->ftp_prov->ftp_mtx);

	/*
	 * Bail out if we can't find the process for this probe or its
	 * provider is defunct (meaning it was valid in a previously exec'ed
	 * incarnation of this address space). The provider can't go away
	 * while we're in this code path.
	 */
	if (probe->ftp_prov->ftp_defunct ||
	    (p = sprlock(probe->ftp_pid)) == NULL)
		return;

	ASSERT(!(p->p_flag & SVFORK));
	mutex_exit(&p->p_lock);

	/*
	 * We have to enable the trap entry before any user threads have
	 * the chance to execute the trap instruction we're about to place
	 * in their process's text.
	 */
	fasttrap_enable_common(&fasttrap_pid_count,
	    &dtrace_pid_probe_ptr, fasttrap_pid_probe,
	    &dtrace_return_probe_ptr, fasttrap_return_probe);

	/*
	 * Enable all the tracepoints and add this probe's id to each
	 * tracepoint's list of active probes.
	 */
	for (i = 0; i < probe->ftp_ntps; i++) {
		if (fasttrap_tracepoint_enable(p, probe, i) != 0) {
			/*
			 * Back up and pull out all the tracepoints we've
			 * created so far for this probe.
			 */
			while (--i >= 0) {
				fasttrap_tracepoint_disable(p, probe, i);
			}

			mutex_enter(&p->p_lock);
			sprunlock(p);

			/*
			 * Since we're not actually enabling this probe,
			 * drop our reference on the trap table entry.
			 */
			fasttrap_disable_common(&fasttrap_pid_count,
			    &dtrace_pid_probe_ptr, &dtrace_return_probe_ptr);
			return;
		}
	}

	mutex_enter(&p->p_lock);
	sprunlock(p);

	probe->ftp_enabled = 1;
}


/*ARGSUSED*/
static void
fasttrap_disable(void *arg, dtrace_id_t id, void *parg)
{
	/*
	 * Disable the probe the corresponds to statically placed trace
	 * points.
	 */
	ASSERT(arg == NULL);
	ASSERT(id == fasttrap_probe_id);
	ASSERT(MUTEX_HELD(&cpu_lock));
	fasttrap_disable_common(&fasttrap_count, &dtrace_fasttrap_probe_ptr,
	    NULL);
}

/*ARGSUSED*/
static void
fasttrap_pid_disable(void *arg, dtrace_id_t id, void *parg)
{
	fasttrap_probe_t *probe = parg;
	fasttrap_provider_t *provider = probe->ftp_prov;
	proc_t *p;
	int i, whack = 0;

	if (!probe->ftp_enabled) {
		mutex_enter(&provider->ftp_mtx);
		provider->ftp_rcount--;
		ASSERT(provider->ftp_rcount >= 0);
		mutex_exit(&provider->ftp_mtx);
		return;
	}

	ASSERT(id == probe->ftp_id);

	/*
	 * We won't be able to acquire a /proc-esque lock on the process
	 * iff the process is dead and gone. In this case, we rely on the
	 * provider lock as a point of mutual exclusion to prevent other
	 * DTrace consumers from disabling this probe.
	 */
	if ((p = sprlock(probe->ftp_pid)) != NULL) {
		ASSERT(!(p->p_flag & SVFORK));
		mutex_exit(&p->p_lock);
	}

	mutex_enter(&provider->ftp_mtx);

	/*
	 * Disable all the associated tracepoints.
	 */
	for (i = 0; i < probe->ftp_ntps; i++) {
		fasttrap_tracepoint_disable(p, probe, i);
	}

	ASSERT(provider->ftp_rcount > 0);
	provider->ftp_rcount--;

	if (p != NULL) {
		/*
		 * Even though we may not be able to remove it entirely, we
		 * mark this defunct provider to get a chance to remove some
		 * of the associated probes.
		 */
		if (provider->ftp_defunct && !provider->ftp_marked)
			whack = provider->ftp_marked = 1;
		mutex_exit(&provider->ftp_mtx);

		mutex_enter(&p->p_lock);