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

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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: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Reviewed-by: Masami 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jason Xing 2025-06-12 14:12:01 +08:00 • committed by Andrew Morton
parent 7f2173894f
commit 19f3cb64a2
2 changed files with 13 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

5
include/linux/relay.h
View file

@ -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 */

18
kernel/relay.c
View file

@ -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)
count += rbuf->stats.full_count;
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;
}
}
}