From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 15 Apr 2014 16:50:12 +0000 (-0400)
Subject: Fix: pass proper args when writing commit counter
X-Git-Tag: v2.4.2~9
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=1f280b069d5fd9ca2cac2a957dab4f657d12a658;p=lttng-modules.git

Fix: pass proper args when writing commit counter

lib_ring_buffer_write_commit_counter()'s 'buf_offset' argument should
contain offset of beginning of area used by the record being comitted.

However, lib_ring_buffer_commit() passes ctx->buf_offset, that gets
advanced by lib_ring_buffer_write() and thus points to just-after-
end-of-record at lib_ring_buffer_commit() time. This causes
lib_ring_buffer_write_commit_counter() to return without changing
commit_hot[idx].seq, due to

	if (unlikely(subbuf_offset(offset - commit_count, chan)))
		return;

Since after-crash data extraction tool checks 'seq' field to find out
how much data is in buffer, this results into inavailability of
data from partially-filled subbuffer for after-crash analysis.

This patch modifies lib_ring_buffer_write_commit_counter() and all its
callers to pass and expect the end of the area. So code works as it
should, and complete information becomes visible in crash dump.

[ Changelog inspired from Nikita Yushchenko's original patch. ]

Fixes #784

Reported-by: Nikita Yushchenko <nyoushchenko@mvista.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/lib/ringbuffer/frontend_api.h b/lib/ringbuffer/frontend_api.h
index 31ccbfad..ff6abce9 100644
--- a/lib/ringbuffer/frontend_api.h
+++ b/lib/ringbuffer/frontend_api.h
@@ -298,8 +298,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	 * ring_buffer buffers from vmcore, after crash.
 	 */
 	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
-					     ctx->buf_offset, commit_count,
-					 ctx->slot_size);
+			offset_end, commit_count);
 }
 
 /**
diff --git a/lib/ringbuffer/frontend_internal.h b/lib/ringbuffer/frontend_internal.h
index eda800de..47c08029 100644
--- a/lib/ringbuffer/frontend_internal.h
+++ b/lib/ringbuffer/frontend_internal.h
@@ -421,23 +421,20 @@ void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *c
 				          struct channel *chan,
 				          unsigned long idx,
 				          unsigned long buf_offset,
-				          unsigned long commit_count,
-				          size_t slot_size)
+				          unsigned long commit_count)
 {
-	unsigned long offset, commit_seq_old;
+	unsigned long commit_seq_old;
 
 	if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 		return;
 
-	offset = buf_offset + slot_size;
-
 	/*
 	 * subbuf_offset includes commit_count_mask. We can simply
 	 * compare the offsets within the subbuffer without caring about
 	 * buffer full/empty mismatch because offset is never zero here
 	 * (subbuffer header and record headers have non-zero length).
 	 */
-	if (unlikely(subbuf_offset(offset - commit_count, chan)))
+	if (unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 		return;
 
 	commit_seq_old = v_read(config, &buf->commit_hot[idx].seq);
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index fc8d5413..86d5398a 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1261,8 +1261,8 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old,
 				      commit_count, oldidx, tsc);
 	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
-					     offsets->old, commit_count,
-					     config->cb.subbuffer_header_size());
+			offsets->old + config->cb.subbuffer_header_size(),
+			commit_count);
 }
 
 /*
@@ -1305,8 +1305,7 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
 				      commit_count, oldidx, tsc);
 	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
-					     offsets->old, commit_count,
-					     padding_size);
+			offsets->old + padding_size, commit_count);
 }
 
 /*
@@ -1348,8 +1347,8 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin,
 				      commit_count, beginidx, tsc);
 	lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx,
-					     offsets->begin, commit_count,
-					     config->cb.subbuffer_header_size());
+			offsets->begin + config->cb.subbuffer_header_size(),
+			commit_count);
 }
 
 /*