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Fri, 28 Nov 2025 09:45:01 GMT Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4D87458059; Fri, 28 Nov 2025 09:45:01 +0000 (GMT) Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A1EB05805B; Fri, 28 Nov 2025 09:44:59 +0000 (GMT) Received: from [9.61.122.162] (unknown [9.61.122.162]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 28 Nov 2025 09:44:59 +0000 (GMT) Message-ID: <6e326cbf-2f19-4619-aa27-3e8b72835b03@linux.ibm.com> Date: Fri, 28 Nov 2025 15:14:58 +0530 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: kernel build failure when CONFIG_DEBUG_INFO_BTF and CONFIG_KCSAN are enabled To: Alan Maguire , Jiri Olsa Cc: bpf@vger.kernel.org, Bart Van Assche , "linux-block@vger.kernel.org" References: <42a1b4b0-83d0-4dda-b1df-15a1b7c7638d@linux.ibm.com> <214308ce-763c-47a8-8719-70564b3ef49c@oracle.com> <65e3ff98-4490-413e-a075-c1df8e7b2bd1@linux.ibm.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTIyMDAyMSBTYWx0ZWRfX2yKjykrERnki mVVQt8xsKIZf54p9Oib6pbqhLEGabHJB05gjCiUQc4M8pSrMWOOpKJyM7w0JEiEAPHZofcaM9Xh AfoeZprpNES+jWWI2AuoL/UgjsESpGrUQUygpzKuJO/iLOGH+NRXIte87z4Yx7HSVR2VeumOAzL Sn54xydFxWV2BILT3ABRDaZnEoTRcQg5NUJ2yWJKlau05m5W5GdTCRMkaBn8GrwWC1excXphBs9 NhgqYe/8KZrN3FIHQeUAHooXQ9bkrz+EKDxdTZx0JCnKTyposFI4W6K4/HoFsVzuOx6zNseNvUC YbFCEYMXob8QVXZvK80OscDKWaZhVoIwAl+gxq6eodcW+TsYpvX4IWKD30MNl/yiSmfXFdVCwiS fJ2R335AmUwgz7DR+WLwVUGttjvsKw== X-Proofpoint-ORIG-GUID: 9Rq8V7FFGK70suPbJD_o94mjVVVXmVbB X-Proofpoint-GUID: iCy5q_o9XRVzPKsK7RnagxGLw1XwhPX2 X-Authority-Analysis: v=2.4 cv=TMJIilla c=1 sm=1 tr=0 ts=69296f1f cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=yPCof4ZbAAAA:8 a=UoiQlHMdomGLu2Lrzl0A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-28_03,2025-11-27_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 phishscore=0 impostorscore=0 clxscore=1015 adultscore=0 bulkscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511220021 On 11/28/25 1:23 PM, Alan Maguire wrote: > On 28/11/2025 06:27, Nilay Shroff wrote: >> >> Hi Alan, >> >> On 11/27/25 9:06 PM, Alan Maguire wrote: >>> On 27/11/2025 11:19, Jiri Olsa wrote: >>>> On Wed, Nov 26, 2025 at 03:59:28PM +0530, Nilay Shroff wrote: >>>>> Hi, >>>>> >>>>> I am encountering the following build failures when compiling the kernel source checked out >>>>> from the for-6.19/block branch [1]: >>>>> >>>>> KSYMS .tmp_vmlinux2.kallsyms.S >>>>> AS .tmp_vmlinux2.kallsyms.o >>>>> LD vmlinux.unstripped >>>>> BTFIDS vmlinux.unstripped >>>>> WARN: multiple IDs found for 'task_struct': 110, 3046 - using 110 >>>>> WARN: multiple IDs found for 'module': 170, 3055 - using 170 >>>>> WARN: multiple IDs found for 'file': 697, 3130 - using 697 >>>>> WARN: multiple IDs found for 'vm_area_struct': 714, 3140 - using 714 >>>>> WARN: multiple IDs found for 'seq_file': 1060, 3167 - using 1060 >>>>> WARN: multiple IDs found for 'cgroup': 2355, 3304 - using 2355 >>>>> WARN: multiple IDs found for 'inode': 553, 3339 - using 553 >>>>> WARN: multiple IDs found for 'path': 586, 3369 - using 586 >>>>> WARN: multiple IDs found for 'bpf_prog': 2565, 3640 - using 2565 >>>>> WARN: multiple IDs found for 'bpf_map': 2657, 3837 - using 2657 >>>>> WARN: multiple IDs found for 'bpf_link': 2849, 3965 - using 2849 >>>>> [...] >>>>> make[2]: *** [scripts/Makefile.vmlinux:72: vmlinux.unstripped] Error 255 >>>>> make[2]: *** Deleting file 'vmlinux.unstripped' >>>>> make[1]: *** [/home/src/linux/Makefile:1242: vmlinux] Error 2 >>>>> make: *** [Makefile:248: __sub-make] Error 2 >>>>> >>>>> >>>>> The build failure appears after commit 42adb2d4ef24 (“fs: Add the __data_racy annotation >>>>> to backing_dev_info.ra_pages”) and commit 935a20d1bebf (“block: Remove queue freezing >>>>> from several sysfs store callbacks”). However, the root cause does not seem to be specific >>>> >>>> yep, looks like __data_racy macro that adds 'volatile' to struct member is causing >>>> the mismatch during deduplication >>>> >>>> when you enable KCSAN some objects may opt out from it (via KCSAN_SANITIZE := n or >>>> such) and they will be compiled without __SANITIZE_THREAD__ macro defined which means >>>> __data_racy will be empty .. and we will get 2 versions of 'struct backing_dev_info' >>>> which cascades up to the task_struct and others >>>> >>>> not sure what's the best solution in here.. could we ignore volatile for >>>> the field in the struct during deduplication? >>>> >>> >>> Yeah, it seems like a slightly looser form of equivalence matching might be needed. >>> The following libbpf change ignores modifiers in type equivalence comparison and >>> resolves the issue for me. It might be too big a hammer though, what do folks think? >>> >>> From 160fb6610d75d3cdc38a9729cc17875a302a7189 Mon Sep 17 00:00:00 2001 >>> From: Alan Maguire >>> Date: Thu, 27 Nov 2025 15:22:04 +0000 >>> Subject: [RFC bpf-next] libbpf: BTF dedup should ignore modifiers in type >>> equivalence checks >>> >>> We see identical type problems in [1] as a result of an occasionally >>> applied volatile modifier to kernel data structures. Such things can >>> result from different header include patterns, explicit Makefile >>> rules etc. As a result consider types with modifiers (const, volatile, >>> restrict, type tag) as equivalent for dedup equivalence testing purposes. >>> >>> [1] https://lore.kernel.org/bpf/42a1b4b0-83d0-4dda-b1df-15a1b7c7638d@linux.ibm.com/ >>> >>> Reported-by: Nilay Shroff >>> Signed-off-by: Alan Maguire >>> --- >>> tools/lib/bpf/btf.c | 27 +++++++++++++++++++++------ >>> 1 file changed, 21 insertions(+), 6 deletions(-) >>> >>> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c >>> index e5003885bda8..384194a6cdae 100644 >>> --- a/tools/lib/bpf/btf.c >>> +++ b/tools/lib/bpf/btf.c >>> @@ -4678,12 +4678,10 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, >>> cand_kind = btf_kind(cand_type); >>> canon_kind = btf_kind(canon_type); >>> >>> - if (cand_type->name_off != canon_type->name_off) >>> - return 0; >>> - >>> /* FWD <--> STRUCT/UNION equivalence check, if enabled */ >>> - if ((cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD) >>> - && cand_kind != canon_kind) { >>> + if ((cand_kind == BTF_KIND_FWD || canon_kind == BTF_KIND_FWD) && >>> + cand_type->name_off == canon_type->name_off && >>> + cand_kind != canon_kind) { >>> __u16 real_kind; >>> __u16 fwd_kind; >>> >>> @@ -4700,7 +4698,24 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, >>> return fwd_kind == real_kind; >>> } >>> >>> - if (cand_kind != canon_kind) >>> + /* >>> + * Types are considered equivalent if modifiers (const, volatile, >>> + * restrict, type tag) are present for one but not the other. >>> + */ >>> + if (cand_kind != canon_kind) { >>> + __u32 next_cand_id = cand_id; >>> + __u32 next_canon_id = canon_id; >>> + >>> + if (btf_is_mod(cand_type)) >>> + next_cand_id = cand_type->type; >>> + if (btf_is_mod(canon_type)) >>> + next_canon_id = canon_type->type; >>> + if (cand_id == next_cand_id && canon_id == next_canon_id) >>> + return 0; >>> + return btf_dedup_is_equiv(d, next_cand_id, next_canon_id); >>> + } >>> + >>> + if (cand_type->name_off != canon_type->name_off) >>> return 0; >>> >>> switch (cand_kind) { >> >> Thanks for your patch! I just applied it on my tree and rebuild the >> tree. However I am still seeing the same compilation warnings. I am >> using the latest for-6.19/block branch[1]. >> >> [1] https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git/log/?h=for-6.19/block >> > > hi Nilay, > > The tricky part with testing this is ensure that pahole is using the updated libbpf > rather than just the kernel itself. Did you "make install" the modified libbpf and > ensure that pahole was using it by building pahole with the cmake option > -DLIBBPF_EMBEDDED=OFF ? That's the easiest way to ensure the change makes it into pahole; > you can check shared library usage using "ldd /usr/local/bin/pahole". The other option > is to apply the change to the embedded libbpf in the lib/bpf directory in pahole. > > I tested the for-6.19/block branch with your config before and after making the > above change and applying it to pahole and things woorked. If that's doable from your > side that would be great. Thanks! > Thanks Alan! And obviously I didn't updated pahole using patched libbpf. Now I have just updated pahole which uses the your patched libbpf. With this change, I confirmed that your patch fixes this compilation warnings for me. # which pahole /usr/local/bin/pahole # ldd /usr/local/bin/pahole | grep libbpf libbpf.so.1 => /usr/local/lib64/libbpf.so.1 (0x00007fffa2fc0000) With this test, please feel free to add, Acked-by: Nilay Shroff