Re: [PATCH v3 3/3] mm: Batch-zap large anonymous folio PTE mappings

[Ryan Roberts]

On 26/07/2023 22:23, Nathan Chancellor wrote:
> On Wed, Jul 26, 2023 at 10:17:18PM +0100, Ryan Roberts wrote:
>> On 26/07/2023 20:50, Nathan Chancellor wrote:
>>> On Wed, Jul 26, 2023 at 08:38:25PM +0100, Ryan Roberts wrote:
>>>> On 26/07/2023 17:19, Nathan Chancellor wrote:
>>>>> Hi Ryan,
>>>>>
>>>>> On Thu, Jul 20, 2023 at 12:29:55PM +0100, Ryan Roberts wrote:
>>>>
>>>> ...
>>>>
>>>>>>
>>>>>
>>>>> After this change in -next as commit 904d9713b3b0 ("mm: batch-zap large
>>>>> anonymous folio PTE mappings"), I see the following splats several times
>>>>> when booting Debian's s390x configuration (which I have mirrored at [1])
>>>>> in QEMU (bisect log below):
>>>>>
>>>>> $ qemu-system-s390x \
>>>>>     -display none \
>>>>>     -nodefaults \
>>>>>     -M s390-ccw-virtio \
>>>>>     -kernel arch/s390/boot/bzImage \
>>>>>     -initrd rootfs.cpio \
>>>>>     -m 512m \
>>>>>     -serial mon:stdio
>>>>
>>>> I'm compiling the kernel for next-20230726 using the s390 cross compiler from kernel.org and the config you linked. Then booting with qemu-system-s390x (tried both distro's 4.2.1 and locally built 8.0.3) and the initrd you provided (tried passing it compressed and uncompressed), but I'm always getting a kernel panic due to not finding a rootfs:
>>>>
>>>> $ qemu-system-s390x \
>>>> 	-display none \
>>>> 	-nodefaults \
>>>> 	-M s390-ccw-virtio \
>>>> 	-kernel arch/s390/boot/bzImage
>>>> 	-initrd ../s390-rootfs.cpio.zst \
>>>> 	-m 512m \
>>>> 	-serial mon:stdio
>>>> KASLR disabled: CPU has no PRNG
>>>> KASLR disabled: CPU has no PRNG
>>>> Linux version 6.5.0-rc3-next-20230726 (ryarob01@e125769) (s390-linux-gcc (GCC) 13.1.0, GNU ld (GNU Binutils) 2.40) #1 SMP Wed Jul 26 19:56:26 BST 2023
>>>> setup: Linux is running under KVM in 64-bit mode
>>>> setup: The maximum memory size is 512MB
>>>> setup: Relocating AMODE31 section of size 0x00003000
>>>> cpu: 1 configured CPUs, 0 standby CPUs
>>>> Write protected kernel read-only data: 4036k
>>>> Zone ranges:
>>>>   DMA      [mem 0x0000000000000000-0x000000007fffffff]
>>>>   Normal   empty
>>>> Movable zone start for each node
>>>> Early memory node ranges
>>>>   node   0: [mem 0x0000000000000000-0x000000001fffffff]
>>>> Initmem setup node 0 [mem 0x0000000000000000-0x000000001fffffff]
>>>> percpu: Embedded 14 pages/cpu s26368 r0 d30976 u57344
>>>> Kernel command line: 
>>>> random: crng init done
>>>> Dentry cache hash table entries: 65536 (order: 7, 524288 bytes, linear)
>>>> Inode-cache hash table entries: 32768 (order: 6, 262144 bytes, linear)
>>>> Built 1 zonelists, mobility grouping on.  Total pages: 129024
>>>> mem auto-init: stack:all(zero), heap alloc:off, heap free:off
>>>> Memory: 507720K/524288K available (3464K kernel code, 788K rwdata, 572K rodata, 796K init, 400K bss, 16568K reserved, 0K cma-reserved)
>>>> SLUB: HWalign=256, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
>>>> rcu: Hierarchical RCU implementation.
>>>> rcu:    RCU restricting CPUs from NR_CPUS=64 to nr_cpu_ids=1.
>>>> rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
>>>> rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
>>>> NR_IRQS: 3, nr_irqs: 3, preallocated irqs: 3
>>>> rcu: srcu_init: Setting srcu_struct sizes based on contention.
>>>> clocksource: tod: mask: 0xffffffffffffffff max_cycles: 0x3b0a9be803b0a9, max_idle_ns: 1805497147909793 ns
>>>> Console: colour dummy device 80x25
>>>> printk: console [ttysclp0] enabled
>>>> pid_max: default: 32768 minimum: 301
>>>> Mount-cache hash table entries: 1024 (order: 1, 8192 bytes, linear)
>>>> Mountpoint-cache hash table entries: 1024 (order: 1, 8192 bytes, linear)
>>>> rcu: Hierarchical SRCU implementation.
>>>> rcu:    Max phase no-delay instances is 1000.
>>>> smp: Bringing up secondary CPUs ...
>>>> smp: Brought up 1 node, 1 CPU
>>>> clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
>>>> futex hash table entries: 256 (order: 4, 65536 bytes, linear)
>>>> kvm-s390: SIE is not available
>>>> hypfs: The hardware system does not support hypfs
>>>> workingset: timestamp_bits=62 max_order=17 bucket_order=0
>>>> io scheduler mq-deadline registered
>>>> io scheduler kyber registered
>>>> cio: Channel measurement facility initialized using format extended (mode autodetected)
>>>> Discipline DIAG cannot be used without z/VM
>>>> vmur: The z/VM virtual unit record device driver cannot be loaded without z/VM
>>>> sclp_sd: Store Data request failed (eq=2, di=3, response=0x40f0, flags=0x00, status=0, rc=-5)
>>>> List of all partitions:
>>>> No filesystem could mount root, tried: 
>>>>
>>>> Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(1,0)
>>>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc3-next-20230726 #1
>>>> Hardware name: QEMU 8561 QEMU (KVM/Linux)
>>>> Call Trace:
>>>>  [<0000000000432b22>] dump_stack_lvl+0x62/0x80 
>>>>  [<0000000000158898>] panic+0x2f8/0x310 
>>>>  [<00000000005b7a56>] mount_root_generic+0x276/0x3b8 
>>>>  [<00000000005b7e46>] prepare_namespace+0x56/0x220 
>>>>  [<00000000004593e8>] kernel_init+0x28/0x1c8 
>>>>  [<000000000010217e>] __ret_from_fork+0x36/0x50 
>>>>  [<000000000046143a>] ret_from_fork+0xa/0x30
>>>>
>>>>
>>>> Any idea what I'm doing wrong here? Do I need to specify something on the kernel command line? (I've tried root=/dev/ram0, but get the same result).
>>>
>>> Hmmm, interesting. The rootfs does need to be used decompressed (I think
>>> the kernel does support zstd compressed initrds but we only compress
>>> them to save space, not for running). Does the sha256sum sum match the
>>> one I just tested?
>>>
>>> $ curl -LSsO https://github.com/ClangBuiltLinux/boot-utils/releases/download/20230707-182910/s390-rootfs.cpio.zst
>>> $ zstd -d s390-rootfs.cpio.zst
>>> $ sha256sum s390-rootfs.cpio
>>> 948fb3c2ad65e26aee8eb0a069f5c9e1ab2c59e4b4f62b63ead271e12a8479b4  s390-rootfs.cpio
>>
>> Yes, this matches.
>>
>>> $ qemu-system-s390x -display none -nodefaults -M s390-ccw-virtio -kernel arch/s390/boot/bzImage -initrd s390-rootfs.cpio -m 512m -serial mon:stdio
>>> ...
>>> [    7.890385] Trying to unpack rootfs image as initramfs...
>>> ...
>>>
>>> I suppose it could be something with Kconfig too, here is the actual one
>>> that olddefconfig produces for me:
>>>
>>> https://gist.github.com/nathanchance/3e4c1721ac204bbb969e2f288e1695c9
>>
>> Ahh, I think this was the problem, after downloading this, the kernel is taking
>> much longer to compile and eventually giving me an assembler error:
>>
>> arch/s390/kernel/mcount.S: Assembler messages:
>> arch/s390/kernel/mcount.S:140: Error: Unrecognized opcode: `aghik'
>> make[4]: *** [scripts/Makefile.build:360: arch/s390/kernel/mcount.o] Error 1
>> make[4]: *** Waiting for unfinished jobs....
>> make[3]: *** [scripts/Makefile.build:480: arch/s390/kernel] Error 2
>> make[2]: *** [scripts/Makefile.build:480: arch/s390] Error 2
>> make[2]: *** Waiting for unfinished jobs....
>> make[1]: *** [/data_nvme0n1/ryarob01/granule_perf/linux/Makefile:2035: .] Error 2
>> make: *** [Makefile:234: __sub-make] Error 2
>>
>> The assembler that comes with the kernel.org toolchain is from binutils 2.40.
>> Perhaps that's too old for this instruction? It's inside an "#ifdef
>> CONFIG_FUNCTION_GRAPH_TRACER" block, so I'm guessing whatever config I was
>> previously using didn't have that enabled. I'll try to disable some configs to
>> workaround. What assembler are you using?
> 
> Ah sorry about that, I forgot about that issue because I handled it
> during my bisect and all the manual reproduction/verification I have
> been doing in this thread has been against Andrew's -mm tree, which does
> not have that problem. Apply this patch on top of next-20230726 and
> everything should work...
> 
> https://lore.kernel.org/20230726061834.1300984-1-hca@xxxxxxxxxxxxx/

No problem - I just got it working by disabling FUNCTION_TRACER, which avoids
aghik, and then disabling generation of BTF (which was complaining that pahole
wasn't available).

Anyway, I'm up and running now - can repro what you are seeing. Although it's
late in the UK now, so will have to look at this tomorrow. Hopefully I can get
to the bottom of it in reasonable time.

> 
> Cheers,
> Nathan