linux-kernel - Re: linux-next: build failure after merge of the block tree

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Message-ID: <ed061c97-9d4f-41c1-a340-1b1e57985e50@kernel.dk>
Date: Fri, 23 Jan 2026 11:06:43 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Mark Brown <broonie@...nel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the block tree

On 1/23/26 11:00 AM, Jens Axboe wrote:
> On 1/23/26 10:42 AM, Mark Brown wrote:
>> Hi all,
>>
>> After merging the block tree, today's linux-next build (x86 allmodconfig)
>> failed like this:
>>
>> In file included from /tmp/next/build/include/linux/string.h:386,
>>                  from /tmp/next/build/include/linux/bitmap.h:13,
>>                  from /tmp/next/build/include/linux/cpumask.h:11,
>>                  from /tmp/next/build/arch/x86/include/asm/paravirt.h:21,
>>                  from /tmp/next/build/arch/x86/include/asm/cpuid/api.h:57,
>>                  from /tmp/next/build/arch/x86/include/asm/processor.h:19,
>>                  from /tmp/next/build/include/linux/sched.h:13,
>>                  from /tmp/next/build/include/linux/io_uring.h:5,
>>                  from /tmp/next/build/io_uring/bpf_filter.c:7:
>> In function 'fortify_memset_chk',
>>     inlined from 'io_uring_populate_bpf_ctx' at /tmp/next/build/io_uring/bpf_filter.c:33:2:
>> /tmp/next/build/include/linux/fortify-string.h:480:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>>   480 |                         __write_overflow_field(p_size_field, size);
>>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> cc1: all warnings being treated as errors
>>
>> Caused by commit
>>
>>   f1e3672e49e2c (io_uring: add support for BPF filtering for opcode restrictions)
> 
> Huh, that am I missing here? The struct looks as follows:
> 
> struct io_uring_bpf_ctx {
> 	__u64	user_data;
> 	__u8	opcode;
> 	__u8	sqe_flags;
> 	__u8	pad[6];
> 	union {
> 		__u64	resv[6];
> 		struct {
> 			__u32	family;
> 			__u32	type;
> 			__u32	protocol;
> 		} socket;
> 		struct {
> 			__u64	flags;
> 			__u64	mode;
> 			__u64	resolve;
> 		} open;
> 	};
> };
> 
> and the offending line is:
> 
> memset(bctx->pad, 0, sizeof(bctx->pad) + sizeof(bctx->resv));
> 
> which should clear from offset 10 (start of pad) for a total of 6 + 48
> bytes, which is 54 bytes. The size of the struct is 64b.
> 
> I guess the part it doesn't like is that it thinks we're clearing the
> pad field, which would of course be way overwriting it. Guess we can do
> something ala:
> 
> memset((void *) bctx + offsetof(struct io_uring_bpf_ctx, pad), 0,
> 	sizeof(bctx->pad) + sizeof(bctx->resv));
> 
> to make it happier.

Folded that in and pushed it out, should be happy for you now. I wonder
if we have a helper for that...

-- 
Jens Axboe