Re: [BUG] regression from 974c5e6139db "xfs: flag as supporting FOP_DONTCACHE" (double free on page?)

[Al Viro <viro@zeniv.linux.org.uk>]

On Sun, May 25, 2025 at 09:32:09AM +0100, Al Viro wrote:
> generic/127 with xfstests built on debian-testing (trixie) ends up with
> assorted memory corruption; trace below is with CONFIG_DEBUG_PAGEALLOC and
> CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT and it looks like a double free
> somewhere in iomap.  Unfortunately, commit in question is just making
> xfs use the infrastructure built in earlier series - not that useful
> for isolating the breakage.

FWIW, the same breakage is reproduced within a couple of iterations of
./check generic/127 on debian-testing image with xfstests built fresh from
git and debian linux-image-6.15-rc7-amd64-unsigned_6.15~rc7-1~exp1_amd64.deb

IOW, it's not something exotic in .config here.  KVM setup is also not
unusual -

kvm \
	-boot order=c \
	-m 16384 \
	-netdev "tap,id=nic0,ifname=tap4,script=no,downscript=no" \
	-device "e1000,netdev=nic0" \
	-nographic \
	-smp 4 \
	-hdb /home/al/emu/ssd/image \
	trixie.img

with image partitioned into two 6G xfs filesystems, with

export TEST_DEV=/dev/sdb1
export TEST_DIR=/home/test
export SCRATCH_DEV=/dev/sdb2
export SCRATCH_MNT=/home/scratch

for local.config.  Bog-standard install, ext4 for everything on sda,
nothing fancy for storage setup - qemu defaults all way through.