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

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Message-ID: <44a91c46-08ba-9693-6c9c-a0a59921e9f1@arm.com>
Date:   Wed, 26 Jul 2023 20:38:25 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Yu Zhao <yuzhao@...gle.com>, Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 3/3] mm: Batch-zap large anonymous folio PTE mappings

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@...5769) (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).

Thanks,
Ryan