Date: Wed, 19 Nov 2025 15:36:29 +1300
From: Tao Liu <ltao@redhat.com>
Subject: [Crash-utility] [PATCH] Add blk_mq_tag_set shared_tags check
To: devel@lists.crash-utility.osci.io
Cc: Tao Liu <ltao@redhat.com>
Message-ID: <20251119023628.15998-2-ltao@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:
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 <ltao@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