On Wed, Aug 6, 2025 at 2:40 PM Lianbo Jiang <[email protected]> wrote:
>
> Hi, Tao
>
> Thank you for the patch.
>
> On 6/27/25 19:33, [email protected] wrote:
> > Date: Fri, 27 Jun 2025 23:30:59 +1200
> > From: Tao Liu<[email protected]>
> > Subject: [Crash-utility] [PATCH] Add blk_mq shared tags support for
> > dev -d/-D
> > To:[email protected]
> > Cc: Tao Liu<[email protected]>
> > Message-ID:<[email protected]>
> > 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<[email protected]>
> > ---
> >
> > 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;
>
> Found a warning here:
>
> gcc -c -g -DX86_64 -DLZO -DGDB_16_2 dev.c -Wall -O2 -Wstrict-prototypes
> -Wmissing-prototypes -fstack-protector -Wformat-security
> dev.c: In function ‘queue_for_each_hw_ctx’:
> dev.c:4415:14: warning: unused variable ‘i’ [-Wunused-variable]
> 4415 | uint i, nr_reserved_tags = 0;
> | ^
>
>
> Other changes are fine to me, so: Ack(with the above fix).
>
Thanks for the comments, will apply it with the corrections.
Thanks,
Tao Liu
>
> Thanks
>
> Lianbo
>
> > + 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
>
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