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

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").

--- 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