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Mon, 09 Jun 2025 17:49:04 -0700 (PDT) From: Jason Xing To: axboe@kernel.dk, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Jason Xing , Yushan Zhou Subject: [PATCH v4 5/5] relayfs: support a counter tracking if data is too big to write Date: Tue, 10 Jun 2025 08:48:44 +0800 Message-Id: <20250610004844.66688-6-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20250610004844.66688-1-kerneljasonxing@gmail.com> References: <20250610004844.66688-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing 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. Reviewed-by: Yushan Zhou Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Jason Xing --- include/linux/relay.h | 5 +++-- kernel/relay.c | 18 ++++++++++-------- 2 files changed, 13 insertions(+), 10 deletions(-) diff --git a/include/linux/relay.h b/include/linux/relay.h index 5310967f9d74..6772a7075840 100644 --- a/include/linux/relay.h +++ b/include/linux/relay.h @@ -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 */ diff --git a/kernel/relay.c b/kernel/relay.c index fd70d0e03216..bcc889dc0970 100644 --- a/kernel/relay.c +++ b/kernel/relay.c @@ -304,6 +304,7 @@ 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; @@ -603,7 +604,7 @@ 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); @@ -663,11 +664,6 @@ 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); @@ -720,11 +716,17 @@ 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; + } } } -- 2.43.5