[PATCH v1] perf session: fix loading of compressed data split across adjacent records

[Alexey Budankov]

Fix decompression failure found during the loading of compressed trace
collected on larger scale systems (>48 cores).

The error happened due to lack of decompression space for a mmaped buffer 
data chunk split across adjacent PERF_RECORD_COMPRESSED records.

  $ perf report -i bt.16384.data --stats
  failed to decompress (B): 63869 -> 0 : Destination buffer is too small
  user stack dump failure
  Can't parse sample, err = -14
  0x2637e436 [0x4080]: failed to process type: 9
  Error:
  failed to process sample

  $ perf test 71
  71: Zstd perf.data compression/decompression              : Ok

Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
---
 tools/perf/util/session.c | 22 ++++++++++++++--------
 tools/perf/util/session.h |  1 +
 tools/perf/util/zstd.c    |  4 ++--
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index d0fd6c614e68..37efa1f43d8b 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -36,10 +36,16 @@ static int perf_session__process_compressed_event(struct perf_session *session,
 	void *src;
 	size_t decomp_size, src_size;
 	u64 decomp_last_rem = 0;
-	size_t decomp_len = session->header.env.comp_mmap_len;
+	size_t mmap_len, decomp_len = session->header.env.comp_mmap_len;
 	struct decomp *decomp, *decomp_last = session->decomp_last;
 
-	decomp = mmap(NULL, sizeof(struct decomp) + decomp_len, PROT_READ|PROT_WRITE,
+	if (decomp_last) {
+		decomp_last_rem = decomp_last->size - decomp_last->head;
+		decomp_len += decomp_last_rem;
+	}
+
+	mmap_len = sizeof(struct decomp) + decomp_len;
+	decomp = mmap(NULL, mmap_len, PROT_READ|PROT_WRITE,
 		      MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
 	if (decomp == MAP_FAILED) {
 		pr_err("Couldn't allocate memory for decompression\n");
@@ -47,10 +53,10 @@ static int perf_session__process_compressed_event(struct perf_session *session,
 	}
 
 	decomp->file_pos = file_offset;
+	decomp->mmap_len = mmap_len;
 	decomp->head = 0;
 
-	if (decomp_last) {
-		decomp_last_rem = decomp_last->size - decomp_last->head;
+	if (decomp_last_rem) {
 		memcpy(decomp->data, &(decomp_last->data[decomp_last->head]), decomp_last_rem);
 		decomp->size = decomp_last_rem;
 	}
@@ -61,7 +67,7 @@ static int perf_session__process_compressed_event(struct perf_session *session,
 	decomp_size = zstd_decompress_stream(&(session->zstd_data), src, src_size,
 				&(decomp->data[decomp_last_rem]), decomp_len - decomp_last_rem);
 	if (!decomp_size) {
-		munmap(decomp, sizeof(struct decomp) + decomp_len);
+		munmap(decomp, mmap_len);
 		pr_err("Couldn't decompress data\n");
 		return -1;
 	}
@@ -255,15 +261,15 @@ static void perf_session__delete_threads(struct perf_session *session)
 static void perf_session__release_decomp_events(struct perf_session *session)
 {
 	struct decomp *next, *decomp;
-	size_t decomp_len;
+	size_t mmap_len;
 	next = session->decomp;
-	decomp_len = session->header.env.comp_mmap_len;
 	do {
 		decomp = next;
 		if (decomp == NULL)
 			break;
 		next = decomp->next;
-		munmap(decomp, decomp_len + sizeof(struct decomp));
+		mmap_len = decomp->mmap_len;
+		munmap(decomp, mmap_len);
 	} while (1);
 }
 
diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
index dd8920b745bc..863dbad87849 100644
--- a/tools/perf/util/session.h
+++ b/tools/perf/util/session.h
@@ -46,6 +46,7 @@ struct perf_session {
 struct decomp {
 	struct decomp *next;
 	u64 file_pos;
+	size_t mmap_len;
 	u64 head;
 	size_t size;
 	char data[];
diff --git a/tools/perf/util/zstd.c b/tools/perf/util/zstd.c
index 23bdb9884576..d2202392ffdb 100644
--- a/tools/perf/util/zstd.c
+++ b/tools/perf/util/zstd.c
@@ -99,8 +99,8 @@ size_t zstd_decompress_stream(struct zstd_data *data, void *src, size_t src_size
 	while (input.pos < input.size) {
 		ret = ZSTD_decompressStream(data->dstream, &output, &input);
 		if (ZSTD_isError(ret)) {
-			pr_err("failed to decompress (B): %ld -> %ld : %s\n",
-			       src_size, output.size, ZSTD_getErrorName(ret));
+			pr_err("failed to decompress (B): %ld -> %ld, dst_size %ld : %s\n",
+			       src_size, output.size, dst_size, ZSTD_getErrorName(ret));
 			break;
 		}
 		output.dst  = dst + output.pos;
-- 
2.20.1