Commit 19f3cb64 authored by Jason Xing's avatar Jason Xing Committed by Andrew Morton
Browse files

relayfs: support a counter tracking if data is too big to write 

It really doesn't matter if the user/admin knows what the last too big
value is.  Record how many times this case is triggered would be helpful.

Solve the existing issue where relay_reset() doesn't restore the value.

Store the counter in the per-cpu buffer structure instead of the global
buffer structure.  It also solves the racy condition which is likely to
happen when a few of per-cpu buffers encounter the too big data case and
then access the global field last_toobig without lock protection.

Remove the printk in relay_close() since kernel module can directly call
relay_stats() as they want.

Link: https://lkml.kernel.org/r/20250612061201.34272-6-kerneljasonxing@gmail.com


Signed-off-by: default avatarJason Xing <kernelxing@tencent.com>
Reviewed-by: default avatarYushan Zhou <katrinzhou@tencent.com>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7f217389

include/linux/relay.h

+3 −2
Original line number Diff line number Diff line
@@ -33,13 +33,15 @@ 
 */

enum {

	RELAY_STATS_BUF_FULL = (1 << 0),

	RELAY_STATS_WRT_BIG = (1 << 1),



	RELAY_STATS_LAST = RELAY_STATS_BUF_FULL,

	RELAY_STATS_LAST = RELAY_STATS_WRT_BIG,

};



struct rchan_buf_stats

{

	unsigned int full_count;	/* counter for buffer full */

	unsigned int big_count;		/* counter for too big to write */

};



/*
@@ -79,7 +81,6 @@ struct rchan 
	const struct rchan_callbacks *cb; /* client callbacks */

	struct kref kref;		/* channel refcount */

	void *private_data;		/* for user-defined data */

	size_t last_toobig;		/* tried to log event > subbuf size */

	struct rchan_buf * __percpu *buf; /* per-cpu channel buffers */

	int is_global;			/* One global buffer ? */

	struct list_head list;		/* for channel list */

kernel/relay.c

+10 −8
Original line number Diff line number Diff line
@@ -303,6 +303,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init) 
	buf->data = buf->start;

	buf->offset = 0;

	buf->stats.full_count = 0;

	buf->stats.big_count = 0;



	for (i = 0; i < buf->chan->n_subbufs; i++)

		buf->padding[i] = 0;
@@ -602,7 +603,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length) 
	return length;



toobig:

	buf->chan->last_toobig = length;

	buf->stats.big_count++;

	return 0;

}

EXPORT_SYMBOL_GPL(relay_switch_subbuf);
@@ -662,11 +663,6 @@ void relay_close(struct rchan *chan) 
			if ((buf = *per_cpu_ptr(chan->buf, i)))

				relay_close_buf(buf);



	if (chan->last_toobig)

		printk(KERN_WARNING "relay: one or more items not logged "

		       "[item size (%zd) > sub-buffer size (%zd)]\n",

		       chan->last_toobig, chan->subbuf_size);



	list_del(&chan->list);

	kref_put(&chan->kref, relay_destroy_channel);

	mutex_unlock(&relay_channels_mutex);
@@ -719,11 +715,17 @@ size_t relay_stats(struct rchan *chan, int flags) 
		rbuf = *per_cpu_ptr(chan->buf, 0);

		if (flags & RELAY_STATS_BUF_FULL)

			count = rbuf->stats.full_count;

		else if (flags & RELAY_STATS_WRT_BIG)

			count = rbuf->stats.big_count;

	} else {

		for_each_online_cpu(i) {

			rbuf = *per_cpu_ptr(chan->buf, i);

			if (rbuf && flags & RELAY_STATS_BUF_FULL)

			if (rbuf) {

				if (flags & RELAY_STATS_BUF_FULL)

					count += rbuf->stats.full_count;

				else if (flags & RELAY_STATS_WRT_BIG)

					count += rbuf->stats.big_count;

			}

		}

	}