Re: [PATCH bpf 3/4] bpf: Ensure unit_size is matched with slab cache object size

[Nathan Chancellor <nathan@kernel.org>]

On Sat, Sep 16, 2023 at 10:38:09AM +0800, Hou Tao wrote:
> Hi,
> 
> On 9/15/2023 2:14 AM, Nathan Chancellor wrote:
> > Hi Hou,
> >
> > On Fri, Sep 08, 2023 at 09:39:22PM +0800, Hou Tao wrote:
> >> From: Hou Tao <houtao1@huawei.com>
> >>
> >> Add extra check in bpf_mem_alloc_init() to ensure the unit_size of
> >> bpf_mem_cache is matched with the object_size of underlying slab cache.
> >> If these two sizes are unmatched, print a warning once and return
> >> -EINVAL in bpf_mem_alloc_init(), so the mismatch can be found early and
> >> the potential issue can be prevented.
> >>
> >> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> >> Signed-off-by: Hou Tao <houtao1@huawei.com>
> >> ---
> >>  kernel/bpf/memalloc.c | 33 +++++++++++++++++++++++++++++++--
> >>  1 file changed, 31 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> >> index 90c1ed8210a2..1c22b90e754a 100644
> >> --- a/kernel/bpf/memalloc.c
> >> +++ b/kernel/bpf/memalloc.c
> >> @@ -486,6 +486,24 @@ static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
> >>  	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
> >>  }
> >>  
> >> +static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)
> >> +{
> >> +	struct llist_node *first;
> >> +	unsigned int obj_size;
> >> +
> >> +	first = c->free_llist.first;
> >> +	if (!first)
> >> +		return 0;
> >> +
> >> +	obj_size = ksize(first);
> >> +	if (obj_size != c->unit_size) {
> >> +		WARN_ONCE(1, "bpf_mem_cache[%u]: unexpected object size %u, expect %u\n",
> >> +			  idx, obj_size, c->unit_size);
> >> +		return -EINVAL;
> >> +	}
> >> +	return 0;
> >> +}
> > I am seeing the warning added by this change as commit c93047255202
> > ("bpf: Ensure unit_size is matched with slab cache object size") when
> > booting ARCH=riscv defconfig in QEMU. I have seen some discussion on the
> > mailing list around this, so I apologize if this is a duplicate report
> > but it sounded like the previously reported instance of this warning was
> > already resolved by some other changeor supposed to be resolved by [1].
> > Unfortunately, I tested both current bpf master (currently at
> > 6bd5bcb18f94) with and without that change and I still see the warning
> > in both cases. The rootfs is available at [2], if it is relevant.
> 
> Thanks for the report. It seems it is a new problem which should be
> fixed by commit d52b59315bf5 ("bpf: Adjust size_index according to the
> value of KMALLOC_MIN_SIZE"), but failed to. However I could not
> reproduce the problem by using the provided steps. Do you configure any
> boot cmd line in your local setup ? I suspect dma_get_cache_alignment()
> returns 64 of 1 in your setup, so slab-96 is rounded up to slab-128.
> Could you please run the attached debug patch and post its output ?

Apologies for the delay, I have been traveling (and will be again
shortly). It seems like your theory could be accurate, as I see:

[    0.120969] ==== bpf_mem_cache: KMALLOC_MIN_SIZE 8 ARCH_KMALLOC_MINALIGN 8 min_align 64

There are no cmdline arguments aside from 'earlycon'. Could the QEMU
version matter here for reproduction purposes, as I am still able to
reproduce with my commands on next-20230919? I am using 8.1.0.

Cheers,
Nathan

> > $ make -skj"$(nproc)" ARCH=riscv CROSS_COMPILE=riscv64-linux- mrproper defconfig Image
> >
> > $ qemu-system-riscv64 \
> >     -display none \
> >     -nodefaults \
> >     -bios default \
> >     -M virt \
> >     -append earlycon \
> >     -kernel arch/riscv/boot/Image \
> >     -initrd riscv-rootfs.cpio \
> >     -m 512m \
> >     -serial mon:stdio
> > ...
> > [    0.000000] Linux version 6.5.0-12679-gc93047255202 (nathan@dev-arch.thelio-3990X) (riscv64-linux-gcc (GCC) 13.2.0, GNU ld (GNU Binutils) 2.41) #1 SMP Thu Sep 14 10:44:41 MST 2023
> > ...
> > [    0.433002] ------------[ cut here ]------------
> > [    0.433128] bpf_mem_cache[0]: unexpected object size 128, expect 96
> > [    0.433585] WARNING: CPU: 0 PID: 1 at kernel/bpf/memalloc.c:500 bpf_mem_alloc_init+0x348/0x354
> > [    0.433810] Modules linked in:
> > [    0.433928] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-12679-gc93047255202 #1
> > [    0.434025] Hardware name: riscv-virtio,qemu (DT)
> > [    0.434105] epc : bpf_mem_alloc_init+0x348/0x354
> > [    0.434140]  ra : bpf_mem_alloc_init+0x348/0x354
> > [    0.434163] epc : ffffffff80112572 ra : ffffffff80112572 sp : ff2000000000bd30
> > [    0.434177]  gp : ffffffff81501588 tp : ff600000018d0000 t0 : ffffffff808cd1a0
> > [    0.434190]  t1 : 0720072007200720 t2 : 635f6d656d5f6670 s0 : ff2000000000bdd0
> > [    0.434202]  s1 : ffffffff80e17620 a0 : 0000000000000037 a1 : ffffffff814866b8
> > [    0.434215]  a2 : 0000000000000000 a3 : 0000000000000001 a4 : 0000000000000000
> > [    0.434227]  a5 : 0000000000000000 a6 : 0000000000000047 a7 : 0000000000000046
> > [    0.434239]  s2 : 000000000000000b s3 : 0000000000000000 s4 : 0000000000000000
> > [    0.434251]  s5 : 0000000000000100 s6 : ffffffff815031f8 s7 : ffffffff8153a610
> > [    0.434264]  s8 : 0000000000000060 s9 : 0000000000000060 s10: 0000000000000000
> > [    0.434276]  s11: ff6000001ffe5410 t3 : ff60000001858f00 t4 : ff60000001858f00
> > [    0.434288]  t5 : ff60000001858000 t6 : ff2000000000bb48
> > [    0.434299] status: 0000000200000120 badaddr: 0000000000000000 cause: 0000000000000003
> > [    0.434394] [<ffffffff80112572>] bpf_mem_alloc_init+0x348/0x354
> > [    0.434492] [<ffffffff80a0f302>] bpf_global_ma_init+0x1c/0x30
> > [    0.434516] [<ffffffff8000212c>] do_one_initcall+0x58/0x19c
> > [    0.434526] [<ffffffff80a0105e>] kernel_init_freeable+0x214/0x27e
> > [    0.434537] [<ffffffff808db4dc>] kernel_init+0x1e/0x10a
> > [    0.434548] [<ffffffff80003386>] ret_from_fork+0xa/0x1c
> > [    0.434618] ---[ end trace 0000000000000000 ]---
> >
> > [1]: https://lore.kernel.org/20230913135943.3137292-1-houtao@huaweicloud.com/
> > [2]: https://github.com/ClangBuiltLinux/boot-utils/releases
> >
> > Cheers,
> > Nathan
> >
> > # bad: [98897dc735cf6635f0966f76eb0108354168fb15] Add linux-next specific files for 20230914
> > # good: [aed8aee11130a954356200afa3f1b8753e8a9482] Merge tag 'pmdomain-v6.6-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/linux-pm
> > git bisect start '98897dc735cf6635f0966f76eb0108354168fb15' 'aed8aee11130a954356200afa3f1b8753e8a9482'
> > # good: [ea1bbd78a48c8b325583e8c0bc2690850cb51807] bcachefs: Fix assorted checkpatch nits
> > git bisect good ea1bbd78a48c8b325583e8c0bc2690850cb51807
> > # bad: [9c4e2139cfa15d769eafd51bf3e051293b106986] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git
> > git bisect bad 9c4e2139cfa15d769eafd51bf3e051293b106986
> > # bad: [4f07b13481ab390108b015da2bc8f560416e48d2] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/qcom/linux.git
> > git bisect bad 4f07b13481ab390108b015da2bc8f560416e48d2
> > # bad: [bcfe98207530e1ea0004f4e5dbd6e7e4d9eb2471] Merge branch 'for-linux-next-fixes' of git://anongit.freedesktop.org/drm/drm-misc
> > git bisect bad bcfe98207530e1ea0004f4e5dbd6e7e4d9eb2471
> > # bad: [95d3e99b1ca8ad3da86c525cc1c00e4ba27592ac] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/wireless/wireless.git
> > git bisect bad 95d3e99b1ca8ad3da86c525cc1c00e4ba27592ac
> > # good: [6836d373943afeeeb8e2989c22aaaa51218a83c6] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc.git
> > git bisect good 6836d373943afeeeb8e2989c22aaaa51218a83c6
> > # good: [3d3e2fb5e45a08a45ae01f0dfaf9621ae0e439f9] Merge branch 'main' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git
> > git bisect good 3d3e2fb5e45a08a45ae01f0dfaf9621ae0e439f9
> > # bad: [51d56d51d3881addaea2c7242ae859155ae75607] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec.git
> > git bisect bad 51d56d51d3881addaea2c7242ae859155ae75607
> > # bad: [1a49f4195d3498fe458a7f5ff7ec5385da70d92e] bpf: Avoid dummy bpf_offload_netdev in __bpf_prog_dev_bound_init
> > git bisect bad 1a49f4195d3498fe458a7f5ff7ec5385da70d92e
> > # bad: [c930472552022bd09aab3cd946ba3f243070d5c7] bpf: Ensure unit_size is matched with slab cache object size
> > git bisect bad c930472552022bd09aab3cd946ba3f243070d5c7
> > # good: [7182e56411b9a8b76797ed7b6095fc84be76dfb0] selftests/bpf: Add kprobe_multi override test
> > git bisect good 7182e56411b9a8b76797ed7b6095fc84be76dfb0
> > # good: [b1d53958b69312e43c118d4093d8f93d3f6f80af] bpf: Don't prefill for unused bpf_mem_cache
> > git bisect good b1d53958b69312e43c118d4093d8f93d3f6f80af
> > # first bad commit: [c930472552022bd09aab3cd946ba3f243070d5c7] bpf: Ensure unit_size is matched with slab cache object size
> 

> From 369f2e59cc6c63c3924f654ba3f8491dba58b87b Mon Sep 17 00:00:00 2001
> From: Hou Tao <houtao1@huawei.com>
> Date: Sat, 16 Sep 2023 10:35:52 +0800
> Subject: [PATCH] bpf: Check the return value of dma_get_cache_alignment()
> 
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
>  kernel/bpf/memalloc.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> index 1c22b90e754a..c8d2c3097c43 100644
> --- a/kernel/bpf/memalloc.c
> +++ b/kernel/bpf/memalloc.c
> @@ -6,6 +6,8 @@
>  #include <linux/irq_work.h>
>  #include <linux/bpf_mem_alloc.h>
>  #include <linux/memcontrol.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/swiotlb.h>
>  #include <asm/local.h>
>  
>  /* Any context (including NMI) BPF specific memory allocator.
> @@ -958,6 +960,14 @@ void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
>  	return !ret ? NULL : ret + LLIST_NODE_SZ;
>  }
>  
> +static unsigned int __kmalloc_minalign(void)
> +{
> +	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
> +	    is_swiotlb_allocated())
> +		return ARCH_KMALLOC_MINALIGN;
> +	return dma_get_cache_alignment();
> +}
> +
>  /* Most of the logic is taken from setup_kmalloc_cache_index_table() */
>  static __init int bpf_mem_cache_adjust_size(void)
>  {
> @@ -992,6 +1002,9 @@ static __init int bpf_mem_cache_adjust_size(void)
>  			size_index[(size - 1) / 8] = index;
>  	}
>  
> +	pr_info("==== bpf_mem_cache: KMALLOC_MIN_SIZE %u ARCH_KMALLOC_MINALIGN %u min_align %u\n",
> +		KMALLOC_MIN_SIZE, ARCH_KMALLOC_MINALIGN, __kmalloc_minalign());
> +
>  	return 0;
>  }
>  subsys_initcall(bpf_mem_cache_adjust_size);
> -- 
> 2.29.2
>