Hi lianbo,
On Wed, Nov 19, 2025 at 10:31 PM lijiang <[email protected]> wrote:
>
> On Wed, Nov 19, 2025 at 12:51 PM <[email protected]>
> wrote:
>>
>> Date: Wed, 19 Nov 2025 15:36:29 +1300
>> From: Tao Liu <[email protected]>
>> Subject: [Crash-utility] [PATCH] Add blk_mq_tag_set shared_tags check
>> To: [email protected]
>> Cc: Tao Liu <[email protected]>
>> Message-ID: <[email protected]>
>> 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
$1 = {name = 0xe4911b "BLK_MQ_F_TAG_HCTX_SHARED", member = 0x0, type =
8192, size = 0, member_offset = 0, member_size = 0,
member_typecode = 0, flags = 0, tagname = 0xd41dfd "(unknown)",
value = 8, vaddr = 0}
[1]:
https://www.mail-archive.com/[email protected]/msg01841.html
>
> static bool blk_mq_is_shared_tags(unsigned int flags)
> {
> return flags & BLK_MQ_F_TAG_HCTX_SHARED;
> }
>
> That can follow the changes once the upstream kernel modifies the value.
>
>> blk_mq_is_shared_tags() check is not sufficient. This patch will add
>> shared_tagsblk_mq_is_shared_tags() check is not sufficient. This patch will
>> add shared_tags
>> member check within blk_mq_tag_set struct as an enhancment.
>
>
> Anyway, this change looks good, so: Ack
>
> Lianbo
>
>> [1]:
>> https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-8/-/blob/c8s/include/linux/blk-mq.h?ref_type=heads#L321
>>
>> Fixes: 62486400d35b ("Add blk_mq shared tags support for dev -d/-D")
>> Signed-off-by: Tao Liu <[email protected]>
>> ---
>> dev.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/dev.c b/dev.c
>> index 8391d71..27318e8 100644
>> --- a/dev.c
>> +++ b/dev.c
>> @@ -4464,7 +4464,7 @@ static void blk_mq_queue_tag_busy_iter(ulong q, ulong
>> *hctx, uint cnt,
>> readmem(addr + OFFSET(blk_mq_tag_set_flags), KVADDR,
>> &flags, sizeof(uint), "blk_mq_tag_set.flags",
>> RETURN_ON_ERROR);
>>
>> - if (blk_mq_is_shared_tags(flags)) {
>> + if (blk_mq_is_shared_tags(flags) &&
>> VALID_MEMBER(blk_mq_tag_set_shared_tags)) {
>> addr = addr + OFFSET(blk_mq_tag_set_shared_tags);
>> queue_for_each_hw_ctx(q, addr, bitmap_tags_is_ptr, dio);
>> return;
>> --
>> 2.47.0
--
Crash-utility mailing list -- [email protected]
To unsubscribe send an email to [email protected]
https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/
Contribution Guidelines: https://github.com/crash-utility/crash/wiki
