[PATCH] Make "dev -d|-D" options parse sbitmap on Linux 4.18 and later

[HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx>]

There have been a few reports that the "dev -d|-D" options displayed
incorrect I/O stats due to racy blk_mq_ctx.rq_* counters.  To fix it,
make the options parse sbitmap to count I/O stats on Linux 4.18 and
later kernels, which include RHEL8 ones.

To do this, adjust to the blk_mq_tags structure of Linux 5.10 through
5.15 kernels, which contain kernel commit 222a5ae03cdd ("blk-mq: Use
pointers for blk_mq_tags bitmap tags") and do not contain ae0f1a732f4a
("blk-mq: Stop using pointers for blk_mq_tags bitmap tags").

Signed-off-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
---
  dev.c | 25 +++++++++++++++++++++++--
  1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/dev.c b/dev.c
index 0172c83ffaea..1685f9302837 100644
--- a/dev.c
+++ b/dev.c
@@ -4339,6 +4339,10 @@ static void bt_for_each(ulong q, ulong tags, ulong sbq, uint reserved, uint nr_r
  static void queue_for_each_hw_ctx(ulong q, ulong *hctx, uint cnt, struct diskio *dio)
  {
  	uint i;
+	int bitmap_tags_is_ptr = 0;
+
+	if (MEMBER_TYPE("blk_mq_tags", "bitmap_tags") == TYPE_CODE_PTR)
+		bitmap_tags_is_ptr = 1;
  
  	for (i = 0; i < cnt; i++) {
  		ulong addr = 0, tags = 0;
@@ -4357,9 +4361,17 @@ static void queue_for_each_hw_ctx(ulong q, ulong *hctx, uint cnt, struct diskio
  
  		if (nr_reserved_tags) {
  			addr = tags + OFFSET(blk_mq_tags_breserved_tags);
+			if (bitmap_tags_is_ptr &&
+			    !readmem(addr, KVADDR, &addr, sizeof(ulong),
+					"blk_mq_tags.bitmap_tags", RETURN_ON_ERROR))
+				break;
  			bt_for_each(q, tags, addr, 1, nr_reserved_tags, dio);
  		}
  		addr = tags + OFFSET(blk_mq_tags_bitmap_tags);
+		if (bitmap_tags_is_ptr &&
+		    !readmem(addr, KVADDR, &addr, sizeof(ulong),
+				"blk_mq_tags.bitmap_tags", RETURN_ON_ERROR))
+			break;
  		bt_for_each(q, tags, addr, 0, nr_reserved_tags, dio);
  	}
  }
@@ -4423,14 +4435,23 @@ get_mq_diskio(unsigned long q, unsigned long *mq_count)
  	unsigned long mctx_addr;
  	struct diskio tmp = {0};
  
-	if (INVALID_MEMBER(blk_mq_ctx_rq_dispatched) ||
-	    INVALID_MEMBER(blk_mq_ctx_rq_completed)) {
+	/*
+	 * Currently this function does not support old blk-mq implementation
+	 * before 12f5b9314545 ("blk-mq: Remove generation seqeunce"), so
+	 * filter them out.
+	 */
+	if (VALID_MEMBER(request_state)) {
+		if (CRASHDEBUG(1))
+			fprintf(fp, "mq: using sbitmap\n");
  		get_mq_diskio_from_hw_queues(q, &tmp);
  		mq_count[0] = tmp.read;
  		mq_count[1] = tmp.write;
  		return;
  	}
  
+	if (CRASHDEBUG(1))
+		fprintf(fp, "mq: using blk_mq_ctx counters\n");
+
  	readmem(q + OFFSET(request_queue_queue_ctx), KVADDR, &queue_ctx,
  		sizeof(ulong), "request_queue.queue_ctx",
  		FAULT_ON_ERROR);
-- 
2.31.1
--
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