[PATCH v2] coresight: tmc-etr: Fix updating buffer in not-snapshot mode.

From: Yabin Cui
Date: Mon Aug 12 2019 - 18:12:03 EST


TMC etr always copies all available data to perf aux buffer, which
may exceed the available space in perf aux buffer. It isn't suitable
for not-snapshot mode, because:
1) It may overwrite previously written data.
2) It may make the perf_event_mmap_page->aux_head report having more
or less data than the reality.

So change to only copy the latest data fitting the available space in
perf aux buffer.

Signed-off-by: Yabin Cui <yabinc@xxxxxxxxxx>
---

v1 -> v2: copy the latest data instead of the earliest data.

---
.../hwtracing/coresight/coresight-tmc-etr.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 17006705287a..676dcb4cf0e2 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1410,9 +1410,10 @@ static void tmc_free_etr_buffer(void *config)
* tmc_etr_sync_perf_buffer: Copy the actual trace data from the hardware
* buffer to the perf ring buffer.
*/
-static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
+static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf,
+ unsigned long to_copy)
{
- long bytes, to_copy;
+ long bytes;
long pg_idx, pg_offset, src_offset;
unsigned long head = etr_perf->head;
char **dst_pages, *src_buf;
@@ -1422,8 +1423,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
pg_idx = head >> PAGE_SHIFT;
pg_offset = head & (PAGE_SIZE - 1);
dst_pages = (char **)etr_perf->pages;
- src_offset = etr_buf->offset;
- to_copy = etr_buf->len;
+ src_offset = etr_buf->offset + etr_buf->len - to_copy;

while (to_copy > 0) {
/*
@@ -1434,6 +1434,8 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
* 3) what is available in the destination page.
* in one iteration.
*/
+ if (src_offset >= etr_buf->size)
+ src_offset -= etr_buf->size;
bytes = tmc_etr_buf_get_data(etr_buf, src_offset, to_copy,
&src_buf);
if (WARN_ON_ONCE(bytes <= 0))
@@ -1454,8 +1456,6 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)

/* Move source pointers */
src_offset += bytes;
- if (src_offset >= etr_buf->size)
- src_offset -= etr_buf->size;
}
}

@@ -1501,7 +1501,11 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
spin_unlock_irqrestore(&drvdata->spinlock, flags);

size = etr_buf->len;
- tmc_etr_sync_perf_buffer(etr_perf);
+ if (!etr_perf->snapshot && size > handle->size) {
+ size = handle->size;
+ lost = true;
+ }
+ tmc_etr_sync_perf_buffer(etr_perf, size);

/*
* In snapshot mode we simply increment the head by the number of byte
--
2.23.0.rc1.153.gdeed80330f-goog