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Subject: Re: linux-next: boot warning from the bpf-next tree
To:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>
Cc:     Yonghong Song <yonghong.song@linux.dev>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>
References: <20230913133436.0eeec4cb@canb.auug.org.au>
 <20230913145919.6060ae61@canb.auug.org.au>
From:   Hou Tao <houtao@huaweicloud.com>
Message-ID: <64f1f578-17e7-a8a8-12f2-6a1a0d98a4af@huaweicloud.com>
Date:   Wed, 13 Sep 2023 15:56:04 +0800
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Hi,

On 9/13/2023 12:59 PM, Stephen Rothwell wrote:
> Hi all,
>
> On Wed, 13 Sep 2023 13:34:36 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>> Today's linux-next boot tests (powerpc pseries_le_defconfig) produced
>> this warning:
>>
>>  ------------[ cut here ]------------
>>  bpf_mem_cache[0]: unexpected object size 16, expect 96
>>  WARNING: CPU: 0 PID: 1 at kernel/bpf/memalloc.c:500 bpf_mem_alloc_init+0x410/0x440
>>  Modules linked in:
>>  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.6.0-rc1-04964-g2e08ed1d459f #1
>>  Hardware name: IBM pSeries (emulated by qemu) POWER8 (raw) 0x4d0200 0xf000004 of:SLOF,HEAD pSeries
>>  NIP:  c0000000003c0890 LR: c0000000003c088c CTR: 0000000000000000
>>  REGS: c000000004783890 TRAP: 0700   Not tainted  (6.6.0-rc1-04964-g2e08ed1d459f)
>>  MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 24000280  XER: 00000000
>>  CFAR: c00000000014cfa0 IRQMASK: 0 
>>  GPR00: c0000000003c088c c000000004783b30 c000000001578c00 0000000000000036 
>>  GPR04: 0000000000000000 c000000002667e18 0000000000000001 0000000000000000 
>>  GPR08: c000000002667ce0 0000000000000001 0000000000000000 0000000044000280 
>>  GPR12: 0000000000000000 c000000002b00000 c000000000011188 0000000000000060 
>>  GPR16: c0000000011f9a30 c000000002920f68 c0000000021fac40 c0000000021fac40 
>>  GPR20: c000000002a3ed88 c000000002921560 c0000000014867f0 c00000000291ccd8 
>>  GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000010 
>>  GPR28: c0000000011f9a30 0000000000000000 000000000000000b c00000007fc9ac40 
>>  NIP [c0000000003c0890] bpf_mem_alloc_init+0x410/0x440
>>  LR [c0000000003c088c] bpf_mem_alloc_init+0x40c/0x440
>>  Call Trace:
>>  [c000000004783b30] [c0000000003c088c] bpf_mem_alloc_init+0x40c/0x440 (unreliable)
>>  [c000000004783c20] [c00000000203d0c0] bpf_global_ma_init+0x5c/0x9c
>>  [c000000004783c50] [c000000000010bc0] do_one_initcall+0x80/0x300
>>  [c000000004783d20] [c000000002004978] kernel_init_freeable+0x30c/0x3b4
>>  [c000000004783df0] [c0000000000111b0] kernel_init+0x30/0x1a0
>>  [c000000004783e50] [c00000000000debc] ret_from_kernel_user_thread+0x14/0x1c
>>  --- interrupt: 0 at 0x0
>>  NIP:  0000000000000000 LR: 0000000000000000 CTR: 0000000000000000
>>  REGS: c000000004783e80 TRAP: 0000   Not tainted  (6.6.0-rc1-04964-g2e08ed1d459f)
>>  MSR:  0000000000000000 <>  CR: 00000000  XER: 00000000
>>  CFAR: 0000000000000000 IRQMASK: 0 
>>  GPR00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR12: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  GPR28: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
>>  NIP [0000000000000000] 0x0
>>  LR [0000000000000000] 0x0
>>  --- interrupt: 0
>>  Code: 3b000000 4bfffcbc 78650020 3c62ffe7 39200001 3d420130 7cc607b4 7ba40020 386382f0 992a1e24 4bd8c631 60000000 <0fe00000> 4bffff40 ea410080 3860fff4 
>>  ---[ end trace 0000000000000000 ]---
>>
>> Presumably related to commit
>>
>>   41a5db8d8161 ("bpf: Add support for non-fix-size percpu mem allocation")
>>
>> (or other commist in that series) from the bpf-next tree.
> Actually it looks like it is some interaction between that commit a
> commits in the bpf tree.

Yes. The warning is due to the checking added in commit c93047255202
("bpf: Ensure unit_size is matched with slab cache object size").
Considering that bpf-next has not merged the patch-set yet, should I
post a patch to bpf tree to fix it ? A fix patch is attached which can
fix the warning in my local setup.

>
>


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From 395d19f1ac747070fce43356cea336b4430afed2 Mon Sep 17 00:00:00 2001
From: Hou Tao <houtao1@huawei.com>
Date: Wed, 13 Sep 2023 15:33:13 +0800
Subject: [PATCH] bpf: Skip unit_size checking for global per-cpu allocator

For global per-cpu allocator, the size of free object in free list
doesn't match with unit_size and now there is no way to get the size of
per-cpu pointer saved in free object, so just skip the checking.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 kernel/bpf/memalloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index aad558cdc70f..0ad175277f89 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -491,6 +491,13 @@ static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)
 	struct llist_node *first;
 	unsigned int obj_size;
 
+	/* For per-cpu allocator, the size of free objects in free list doesn't
+	 * match with unit_size and now there is no way to get the size of
+	 * per-cpu pointer saved in free object, so just skip the checking.
+	 */
+	if (c->percpu_size)
+		return 0;
+
 	first = c->free_llist.first;
 	if (!first)
 		return 0;
-- 
2.29.2


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