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

Hi lianbo, Kindly ping for this patch... Sorry about it. I will take a look next week.

Thanks, Tao Liu On Fri, Jun 27, 2025 at 11:33 PM Tao Liu <ltao(a)redhat.com&gt; wrote: > > 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 <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 >