Re: [PATCH v6 4/6] connector/cn_proc: Performance improvements

[Anjali Kulkarni]

> On Jun 30, 2023, at 1:34 PM, Liam Howlett <liam.howlett@xxxxxxxxxx> wrote:
> 
> * Anjali Kulkarni <anjali.k.kulkarni@xxxxxxxxxx> [230614 19:41]:
>> This patch adds the capability to filter messages sent by the proc
>> connector on the event type supplied in the message from the client
>> to the connector. The client can register to listen for an event type
>> given in struct proc_input.
>> 
>> This event based filteting will greatly enhance performance - handling
>> 8K exits takes about 70ms, whereas 8K-forks + 8K-exits takes about 150ms
>> & handling 8K-forks + 8K-exits + 8K-execs takes 200ms. There are currently
>> 9 different types of events, and we need to listen to all of them. Also,
>> measuring the time using pidfds for monitoring 8K process exits took
>> much longer - 200ms, as compared to 70ms using only exit notifications of
>> proc connector.
>> 
>> We also add a new event type - PROC_EVENT_NONZERO_EXIT, which is
>> only sent by kernel to a listening application when any process exiting,
>> has a non-zero exit status. This will help the clients like Oracle DB,
>> where a monitoring process wants notfications for non-zero process exits
>> so it can cleanup after them.
>> 
>> This kind of a new event could also be useful to other applications like
>> Google's lmkd daemon, which needs a killed process's exit notification.
>> 
>> The patch takes care that existing clients using old mechanism of not
>> sending the event type work without any changes.
>> 
>> cn_filter function checks to see if the event type being notified via
>> proc connector matches the event type requested by client, before
>> sending(matches) or dropping(does not match) a packet.
>> 
>> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@xxxxxxxxxx>
>> ---
>> drivers/connector/cn_proc.c | 64 ++++++++++++++++++++++++++++++++----
>> include/uapi/linux/cn_proc.h | 19 +++++++++++
>> 2 files changed, 77 insertions(+), 6 deletions(-)
>> 
>> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
>> index 84f38d2bd4b9..825d5f506919 100644
>> --- a/drivers/connector/cn_proc.c
>> +++ b/drivers/connector/cn_proc.c
>> @@ -50,21 +50,47 @@ static DEFINE_PER_CPU(struct local_event, local_event) = {
>> 
>> static int cn_filter(struct sock *dsk, struct sk_buff *skb, void *data)
>> {
>> +	uintptr_t val;
>> +	__u32 what, exit_code, *ptr;
>> 	enum proc_cn_mcast_op mc_op;
> 
> I guess reverse xmas tree would be requested here as well?

Will add here.

> 
>> 
>> -	if (!dsk)
>> +	if (!dsk || !data)
>> 		return 0;
>> 
>> +	ptr = (__u32 *)data;
>> +	what = *ptr++;
>> +	exit_code = *ptr;
>> +	val = ((struct proc_input *)(dsk->sk_user_data))->event_type;
>> 	mc_op = ((struct proc_input *)(dsk->sk_user_data))->mcast_op;
>> 
>> 	if (mc_op == PROC_CN_MCAST_IGNORE)
>> 		return 1;
>> 
>> -	return 0;
>> +	if ((__u32)val == PROC_EVENT_ALL)
>> +		return 0;
>> +
>> +	/*
>> +	 * Drop packet if we have to report only non-zero exit status
>> +	 * (PROC_EVENT_NONZERO_EXIT) and exit status is 0
>> +	 */
>> +	if (((__u32)val & PROC_EVENT_NONZERO_EXIT) &&
>> +	 (what == PROC_EVENT_EXIT)) {
>> +		if (exit_code)
>> +			return 0;
>> +		else
> 
> Nit: don't really need the else here.

Will remove it.

> 
>> +			return 1;
>> +	}
>> +
>> +	if ((__u32)val & what)
>> +		return 0;
>> +
>> +	return 1;
>> }
>> 
>> static inline void send_msg(struct cn_msg *msg)
>> {
>> +	__u32 filter_data[2];
>> +
>> 	local_lock(&local_event.lock);
>> 
>> 	msg->seq = __this_cpu_inc_return(local_event.count) - 1;
>> @@ -76,8 +102,16 @@ static inline void send_msg(struct cn_msg *msg)
>> 	 *
>> 	 * If cn_netlink_send() fails, the data is not sent.
>> 	 */
>> +	filter_data[0] = ((struct proc_event *)msg->data)->what;
>> +	if (filter_data[0] == PROC_EVENT_EXIT) {
>> +		filter_data[1] =
>> +		((struct proc_event *)msg->data)->event_data.exit.exit_code;
>> +	} else {
>> +		filter_data[1] = 0;
>> +	}
>> +
>> 	cn_netlink_send_mult(msg, msg->len, 0, CN_IDX_PROC, GFP_NOWAIT,
>> -			 cn_filter, NULL);
>> +			 cn_filter, (void *)filter_data);
>> 
>> 	local_unlock(&local_event.lock);
>> }
>> @@ -357,12 +391,15 @@ static void cn_proc_ack(int err, int rcvd_seq, int rcvd_ack)
>> 
>> /**
>> * cn_proc_mcast_ctl
>> - * @data: message sent from userspace via the connector
>> + * @msg: message sent from userspace via the connector
>> + * @nsp: NETLINK_CB of the client's socket buffer
>> */
>> static void cn_proc_mcast_ctl(struct cn_msg *msg,
>> 			 struct netlink_skb_parms *nsp)
>> {
>> 	enum proc_cn_mcast_op mc_op = 0, prev_mc_op = 0;
>> +	struct proc_input *pinput = NULL;
>> +	enum proc_cn_event ev_type = 0;
>> 	int err = 0, initial = 0;
>> 	struct sock *sk = NULL;
>> 
>> @@ -381,10 +418,21 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
>> 		goto out;
>> 	}
>> 
>> -	if (msg->len == sizeof(mc_op))
>> +	if (msg->len == sizeof(*pinput)) {
>> +		pinput = (struct proc_input *)msg->data;
>> +		mc_op = pinput->mcast_op;
>> +		ev_type = pinput->event_type;
>> +	} else if (msg->len == sizeof(mc_op)) {
>> 		mc_op = *((enum proc_cn_mcast_op *)msg->data);
>> -	else
>> +		ev_type = PROC_EVENT_ALL;
>> +	} else {
>> 		return;
>> +	}
>> +
>> +	ev_type = valid_event((enum proc_cn_event)ev_type);
>> +
>> +	if (ev_type == PROC_EVENT_NONE)
>> +		ev_type = PROC_EVENT_ALL;
>> 
>> 	if (nsp->sk) {
>> 		sk = nsp->sk;
>> @@ -396,6 +444,8 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
>> 			prev_mc_op =
>> 			((struct proc_input *)(sk->sk_user_data))->mcast_op;
>> 		}
>> +		((struct proc_input *)(sk->sk_user_data))->event_type =
>> +			ev_type;
>> 		((struct proc_input *)(sk->sk_user_data))->mcast_op = mc_op;
>> 	}
>> 
>> @@ -407,6 +457,8 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
>> 	case PROC_CN_MCAST_IGNORE:
>> 		if (!initial && (prev_mc_op != PROC_CN_MCAST_IGNORE))
>> 			atomic_dec(&proc_event_num_listeners);
>> +		((struct proc_input *)(sk->sk_user_data))->event_type =
>> +			PROC_EVENT_NONE;
>> 		break;
>> 	default:
>> 		err = EINVAL;
>> diff --git a/include/uapi/linux/cn_proc.h b/include/uapi/linux/cn_proc.h
>> index 6a06fb424313..f2afb7cc4926 100644
>> --- a/include/uapi/linux/cn_proc.h
>> +++ b/include/uapi/linux/cn_proc.h
>> @@ -30,6 +30,15 @@ enum proc_cn_mcast_op {
>> 	PROC_CN_MCAST_IGNORE = 2
>> };
>> 
>> +#define PROC_EVENT_ALL (PROC_EVENT_FORK | PROC_EVENT_EXEC | PROC_EVENT_UID | \
>> +			PROC_EVENT_GID | PROC_EVENT_SID | PROC_EVENT_PTRACE | \
>> +			PROC_EVENT_COMM | PROC_EVENT_NONZERO_EXIT | \
>> +			PROC_EVENT_COREDUMP | PROC_EVENT_EXIT)
>> +
>> +/*
>> + * If you add an entry in proc_cn_event, make sure you add it in
>> + * PROC_EVENT_ALL above as well.
>> + */
>> enum proc_cn_event {
>> 	/* Use successive bits so the enums can be used to record
>> 	 * sets of events as well
>> @@ -45,15 +54,25 @@ enum proc_cn_event {
>> 	/* "next" should be 0x00000400 */
>> 	/* "last" is the last process event: exit,
>> 	 * while "next to last" is coredumping event
>> +	 * before that is report only if process dies
>> +	 * with non-zero exit status
>> 	 */
>> +	PROC_EVENT_NONZERO_EXIT = 0x20000000,
>> 	PROC_EVENT_COREDUMP = 0x40000000,
>> 	PROC_EVENT_EXIT = 0x80000000
>> };
>> 
>> struct proc_input {
>> 	enum proc_cn_mcast_op mcast_op;
>> +	enum proc_cn_event event_type;
>> };
>> 
>> +static inline enum proc_cn_event valid_event(enum proc_cn_event ev_type)
>> +{
>> +	ev_type &= PROC_EVENT_ALL;
>> +	return ev_type;
>> +}
>> +
>> /*
>> * From the user's point of view, the process
>> * ID is the thread group ID and thread ID is the internal
>> -- 
>> 2.41.0