[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&gt; wrote: > > On Wed, Nov 19, 2025 at 12:51 PM < devel-request(a)lists.crash-utility.osci.io&gt; wrote: >> >> Date: Wed, 19 Nov 2025 15:36:29 +1300 >> From: Tao Liu <ltao(a)redhat.com&gt; >> 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&gt; >> Message-ID: <20251119023628.15998-2-ltao(a)redhat.com&gt; >> 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().

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&gt; >> --- >> 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