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

Jens Axboe
2026-01-23T18:00:59Z

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.

--
Jens Axboe