[Crash-utility] Re: [PATCH] Add blk_mq_tag_set shared_tags check
Hi lianbo,
On Wed, Nov 19, 2025 at 10:31 PM lijiang <lijiang(a)redhat.com> wrote:
On Wed, Nov 19, 2025 at 12:51 PM <devel-request(a)lists.crash-utility.osci.io>
wrote:
>
> Date: Wed, 19 Nov 2025 15:36:29 +1300
> From: Tao Liu <ltao(a)redhat.com>
> Subject: [Crash-utility] [PATCH] Add blk_mq_tag_set shared_tags check
> To: devel(a)lists.crash-utility.osci.io
> Cc: Tao Liu <ltao(a)redhat.com>
> Message-ID: <20251119023628.15998-2-ltao(a)redhat.com>
> Content-Type: text/plain; charset="US-ASCII"; x-default=true
>
> A regression of cmd dev -d/-D noticed on some vmcores as:
>
> dev: invalid structure member offset: blk_mq_tag_set_shared_tags
> FILE: dev.c LINE: 4468 FUNCTION: blk_mq_queue_tag_busy_iter()
>
> MAJOR GENDISK NAME REQUEST_QUEUE TOTAL ASYNC SYNC
> [crash] error trace: 91aa85 => 91a552 => 94d6ba => 94d647
>
> 94d647: OFFSET_verify.part.0+55
> 94d6ba: OFFSET_verify+42
> 91a552: get_diskio_1+2194
> 91aa85: display_all_diskio+1253
>
> The root cause is, though upstream kernel have defined BLK_MQ_F_TAG_HCTX_SHARED
> as (1 << 3), the value might be set different, e.g. [1]. So a single
We should be able to get the value of BLK_MQ_F_TAG_HCTX_SHARED via the
dump_enumerator_list(), and then test it in the following function:
Please see [1], I removed (1<<3) and resolved it at runtime.
dump_enumerator_list() is not appropriate, but I used
arg_to_datatype().
In dump_enumerator_list("BLK_MQ_F_TAG_HCTX_SHARED"),
if (!arg_to_datatype(e, dm, RETURN_ON_ERROR) ||
(dm->size < 0) || (dm->type != ENUM) || dm->tagname)
dm->tagname is not NULL and will make dump_enumerator_list return false:
(gdb) p dm
$1 = {name = 0xe4911b "BLK_MQ_F_TAG_HCTX_SHARED", member = 0x0, type =
8192, size = 0, member_offset = 0, member_size = 0,
member_typecode = 0, flags = 0, tagname = 0xd41dfd "(unknown)",
value = 8, vaddr = 0}
[1]: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01841.html
static bool blk_mq_is_shared_tags(unsigned int flags)
{
return flags & BLK_MQ_F_TAG_HCTX_SHARED;
}
That can follow the changes once the upstream kernel modifies the value.
> blk_mq_is_shared_tags() check is not sufficient. This patch will add
shared_tagsblk_mq_is_shared_tags() check is not sufficient. This patch will add
shared_tags
> member check within blk_mq_tag_set struct as an enhancment.
Anyway, this change looks good, so: Ack
Lianbo
> [1]:
https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-8/-/blob...
>
> Fixes: 62486400d35b ("Add blk_mq shared tags support for dev -d/-D")
> Signed-off-by: Tao Liu <ltao(a)redhat.com>
> ---
> dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/dev.c b/dev.c
> index 8391d71..27318e8 100644
> --- a/dev.c
> +++ b/dev.c
> @@ -4464,7 +4464,7 @@ static void blk_mq_queue_tag_busy_iter(ulong q, ulong *hctx,
uint cnt,
> readmem(addr + OFFSET(blk_mq_tag_set_flags), KVADDR,
> &flags, sizeof(uint), "blk_mq_tag_set.flags",
RETURN_ON_ERROR);
>
> - if (blk_mq_is_shared_tags(flags)) {
> + if (blk_mq_is_shared_tags(flags) &&
VALID_MEMBER(blk_mq_tag_set_shared_tags)) {
> addr = addr + OFFSET(blk_mq_tag_set_shared_tags);
> queue_for_each_hw_ctx(q, addr, bitmap_tags_is_ptr, dio);
> return;
> --
> 2.47.0