linux-kernel - Re: [REGRESSION] 9pfs issues on 6.12-rc1

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Message-ID: <ZxZ4-9guCQdAQLpu@Antony2201.local>
Date: Mon, 21 Oct 2024 17:53:31 +0200
From: Antony Antony <antony@...nome.org>
To: David Howells <dhowells@...hat.com>
Cc: Antony Antony <antony@...nome.org>, Sedat Dilek <sedat.dilek@...il.com>,
	Maximilian Bosch <maximilian@...sch.me>,
	Linux regressions mailing list <regressions@...ts.linux.dev>,
	LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	Christian Brauner <brauner@...nel.org>
Subject: Re: [REGRESSION] 9pfs issues on 6.12-rc1

On Mon, Oct 21, 2024 at 03:45:50PM +0100, David Howells wrote:
> Can you tell me what parameters you're mounting 9p with?  Looking at the
> backtrace:
> 
> [   32.390878]  bad_page+0x70/0x110
> [   32.391056]  free_unref_page+0x363/0x4f0
> [   32.391257]  p9_release_pages+0x41/0x90 [9pnet]
> [   32.391627]  p9_virtio_zc_request+0x3d4/0x720 [9pnet_virtio]
> [   32.391896]  ? p9pdu_finalize+0x32/0xa0 [9pnet]
> [   32.392153]  p9_client_zc_rpc.constprop.0+0x102/0x310 [9pnet]
> [   32.392447]  ? kmem_cache_free+0x36/0x370
> [   32.392703]  p9_client_read_once+0x1a6/0x310 [9pnet]
> [   32.392992]  p9_client_read+0x56/0x80 [9pnet]
> [   32.393238]  v9fs_issue_read+0x50/0xd0 [9p]
> [   32.393467]  netfs_read_to_pagecache+0x20c/0x480 [netfs]
> [   32.393832]  netfs_readahead+0x225/0x330 [netfs]
> [   32.394154]  read_pages+0x6a/0x250
> 
> it's using buffered I/O, but when I try and use 9p from qemu, it wants to use
> unbuffered/direct I/O.

how can I check what it is using?
could you see from the command line? 

/nix/store/s7zgdx5i9gs4abxjl94jcsw3xn4m861i-qemu-host-cpu-only-for-vm-tests-9.1.0/bin/qemu-kvm -cpu max -name machine -m 1024 -smp 1 -device virtio-rng-pci -net nic,netdev=user.0,model=virtio -netdev user,id=user.0, -virtfs local,path=/nix/store,security_model=none,mount_tag=nix-store -virtfs local,path=/build/shared-xchg,security_model=none,mount_tag=shared -virtfs local,path=/build/vm-state-machine/xchg,security_model=none,mount_tag=xchg -drive cache=writeback,file=/build/vm-state-machine/machine.qcow2,id=drive1,if=none,index=1,werror=report -device virtio-blk-pci,bootindex=1,drive=drive1,serial=root -device virtio-net-pci,netdev=vlan1,mac=52:54:00:12:01:01 -netdev vde,id=vlan1,sock=/build/vde1.ctl -device virtio-keyboard -usb -device usb-tablet,bus=usb-bus.0 -kernel /nix/store/i4xrqfq4jrk2chv6iqm2rgxdk8biynlr-nixos-system-machine-test/kernel -initrd /nix/store/i06b3wvd4c83x8slnd1f85dj7msjy398-initrd-linux-6.12-rc3/initrd -append console=ttyS0 console=tty0 panic=1 boot.panic_on_fail clocksource=acpi_pm loglevel=7 net.ifnames=0 init=/nix/store/i4xrqfq4jrk2chv6iqm2rgxdk8biynlr-nixos-system-machine-test/init regInfo=/nix/store/5ygkzfld2zk20cy95iipmw2xxfvqalaz-closure-info/registration console=ttyS0  -qmp unix:/build/vm-state-machine/qmp,server=on,wait=off -monitor unix:/build/vm-state-machine/monitor -chardev socket,id=shell,path=/build/vm-state-machine/shell -device virtio-serial -device virtconsole,chardev=shell -device virtio-rng-pci -serial stdio -no-reboot -nographic

or inside a guest (running similar test an older kernel)

>>> print(alice.execute("mount | grep 9p")[1])
nix-store on /nix/.ro-store type 9p (rw,relatime,dirsync,loose,access=client,msize=16384,trans=virtio)
shared on /tmp/shared type 9p (rw,relatime,sync,dirsync,access=client,msize=16384,trans=virtio)
xchg on /tmp/xchg type 9p (rw,relatime,sync,dirsync,access=client,msize=16384,trans=virtio)

-antony