[Crash-utility] Re: [PATCH] Add blk_mq shared tags support for dev -d/-D

Date: Fri, 27 Jun 2025 23:30:59 +1200 From: Tao Liu&lt;ltao(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] Add blk_mq shared tags support for dev -d/-D To:devel@lists.crash-utility.osci.io Cc: Tao Liu&lt;ltao(a)redhat.com&gt; Message-ID:<20250627113058.42612-2-ltao@redhat.com> Content-Type: text/plain; charset="US-ASCII"; x-default=true When blk_mq shared tags enabled for devices like scsi, the IO status is incorrect, e.g: crash> dev -d MAJOR GENDISK NAME REQUEST_QUEUE TOTAL ASYNC SYNC 8 ffff90528df86000 sda ffff9052a3d61800 144 144 0 8 ffff905280718c00 sdb ffff9052a3d63c00 48 48 0 crash> epython rqlist ffff90528e94a5c0 sda is unknown, deadline: 89.992 (90) rq_alloc: 0.196 ffff90528e92f700 sda is unknown, deadline: 89.998 (90) rq_alloc: 0.202 ffff90528e95ccc0 sda is unknown, deadline: 89.999 (90) rq_alloc: 0.203 ffff90528e968bc0 sdb is unknown, deadline: 89.997 (90) rq_alloc: 0.201 The root cause is: for shared tags case, only the shared tags are put into count. Without this patch, tags of all the hw_ctx are counted, which is incorrect. After apply the patch: crash> dev -d MAJOR GENDISK NAME REQUEST_QUEUE TOTAL READ WRITE 8 ffff90528df86000 sda ffff9052a3d61800 3 3 0 8 ffff905280718c00 sdb ffff9052a3d63c00 1 1 0 This patch makes the following modification: 1) blk_mq shared tag support. 2) Function renaming: queue_for_each_hw_ctx -> blk_mq_queue_tag_busy_iter, because the latter is more close to the corresponding kernel function. 3) Extract a new queue_for_each_hw_ctx() function to be called for both shared-tags case and the hw_ctx case. Note: The patch is safe for earlier kernels which have no blk_mq shared tags implemented, because the blk_mq_is_shared_tags() check will exit safely. Signed-off-by: Tao Liu&lt;ltao(a)redhat.com&gt; --- Please discard the previous patch "Filter repeated rq for cmd dev -d/-D", because filtering is an incorrect fix. --- defs.h | 3 ++ dev.c | 96 ++++++++++++++++++++++++++++++++++++++----------------- symbols.c | 6 ++++ 3 files changed, 76 insertions(+), 29 deletions(-) diff --git a/defs.h b/defs.h index bbd6d4b..4fecb83 100644 --- a/defs.h +++ b/defs.h @@ -2271,6 +2271,9 @@ struct offset_table { /* stash of commonly-used offsets */ long task_struct_thread_context_x28; long neigh_table_hash_heads; long neighbour_hash; + long request_queue_tag_set; + long blk_mq_tag_set_flags; + long blk_mq_tag_set_shared_tags; }; struct size_table { /* stash of commonly-used sizes */ diff --git a/dev.c b/dev.c index 9d38aef..0a4d5c9 100644 --- a/dev.c +++ b/dev.c @@ -4326,6 +4326,12 @@ struct bt_iter_data { #define MQ_RQ_IN_FLIGHT 1 #define REQ_OP_BITS 8 #define REQ_OP_MASK ((1 << REQ_OP_BITS) - 1) +#define BLK_MQ_F_TAG_HCTX_SHARED (1 << 3) + +static bool blk_mq_is_shared_tags(unsigned int flags) +{ + return flags & BLK_MQ_F_TAG_HCTX_SHARED; +} static uint op_is_write(uint op) { @@ -4403,43 +4409,72 @@ static void bt_for_each(ulong q, ulong tags, ulong sbq, uint reserved, uint nr_r sbitmap_for_each_set(&sc, bt_iter, &iter_data); } -static void queue_for_each_hw_ctx(ulong q, ulong *hctx, uint cnt, struct diskio *dio) +static bool queue_for_each_hw_ctx(ulong q, ulong blk_mq_tags_ptr, + bool bitmap_tags_is_ptr, struct diskio *dio) { - uint i; + uint i, nr_reserved_tags = 0;

+ ulong tags = 0, addr = 0; + bool ret = FALSE; + + if (!readmem(blk_mq_tags_ptr, KVADDR, &tags, sizeof(ulong), + "blk_mq_hw_ctx.tags", RETURN_ON_ERROR)) + goto out; + + addr = tags + OFFSET(blk_mq_tags_nr_reserved_tags); + if (!readmem(addr, KVADDR, &nr_reserved_tags, sizeof(uint), + "blk_mq_tags_nr_reserved_tags", RETURN_ON_ERROR)) + goto out; + + 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)) + goto out; + 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)) + goto out; + bt_for_each(q, tags, addr, 0, nr_reserved_tags, dio); + + ret = TRUE; +out: + return ret; +} + +/* + * Replica of kernel block/blk-mq-tag.c:blk_mq_queue_tag_busy_iter() +*/ +static void blk_mq_queue_tag_busy_iter(ulong q, ulong *hctx, uint cnt, + struct diskio *dio) +{ + uint i, flags; int bitmap_tags_is_ptr = 0; + ulong addr = 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; - uint nr_reserved_tags = 0; + readmem(q + OFFSET(request_queue_tag_set), KVADDR, &addr, + sizeof(ulong), "request_queue.tag_set", RETURN_ON_ERROR); - /* Tags owned by the block driver */ - addr = hctx[i] + OFFSET(blk_mq_hw_ctx_tags); - if (!readmem(addr, KVADDR, &tags, sizeof(ulong), - "blk_mq_hw_ctx.tags", RETURN_ON_ERROR)) - break; + readmem(addr + OFFSET(blk_mq_tag_set_flags), KVADDR, + &flags, sizeof(uint), "blk_mq_tag_set.flags", RETURN_ON_ERROR); - addr = tags + OFFSET(blk_mq_tags_nr_reserved_tags); - if (!readmem(addr, KVADDR, &nr_reserved_tags, sizeof(uint), - "blk_mq_tags_nr_reserved_tags", RETURN_ON_ERROR)) - break; + if (blk_mq_is_shared_tags(flags)) { + addr = addr + OFFSET(blk_mq_tag_set_shared_tags); + queue_for_each_hw_ctx(q, addr, bitmap_tags_is_ptr, dio); + return; + } - 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); + for (i = 0; i < cnt; i++) { + /* Tags owned by the block driver */ + addr = hctx[i] + OFFSET(blk_mq_hw_ctx_tags); + if (queue_for_each_hw_ctx(q, addr, bitmap_tags_is_ptr, dio) == FALSE) + return; } } @@ -4489,7 +4524,7 @@ static void get_mq_diskio_from_hw_queues(ulong q, struct diskio *dio) return; } - queue_for_each_hw_ctx(q, hctx_array, cnt, dio); + blk_mq_queue_tag_busy_iter(q, hctx_array, cnt, dio); FREEBUF(hctx_array); } @@ -4914,6 +4949,9 @@ void diskio_init(void) MEMBER_SIZE_INIT(class_private_devices, "class_private", "class_devices"); MEMBER_OFFSET_INIT(disk_stats_in_flight, "disk_stats", "in_flight"); + MEMBER_OFFSET_INIT(request_queue_tag_set, "request_queue", "tag_set"); + MEMBER_OFFSET_INIT(blk_mq_tag_set_flags, "blk_mq_tag_set", "flags"); + MEMBER_OFFSET_INIT(blk_mq_tag_set_shared_tags, "blk_mq_tag_set", "shared_tags"); dt->flags |= DISKIO_INIT; } diff --git a/symbols.c b/symbols.c index e30fafe..794519a 100644 --- a/symbols.c +++ b/symbols.c @@ -11487,6 +11487,12 @@ dump_offset_table(char *spec, ulong makestruct) OFFSET(blk_mq_tags_nr_reserved_tags)); fprintf(fp, " blk_mq_tags_rqs: %ld\n", OFFSET(blk_mq_tags_rqs)); + fprintf(fp, " request_queue_tag_set: %ld\n", + OFFSET(request_queue_tag_set)); + fprintf(fp, " blk_mq_tag_set_flags: %ld\n", + OFFSET(blk_mq_tag_set_flags)); + fprintf(fp, " blk_mq_tag_set_shared_tags: %ld\n", + OFFSET(blk_mq_tag_set_shared_tags)); fprintf(fp, " subsys_private_subsys: %ld\n", OFFSET(subsys_private_subsys)); fprintf(fp, " subsys_private_klist_devices: %ld\n", -- 2.47.0