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

[Ryan Roberts <ryan.roberts@arm.com>]

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?



> 
> Cheers,
> Nathan