From: Gao Xiang hsiangkao@redhat.com Subject: mm, THP, swap: fix allocating cluster for swapfile by mistake

SWP_FS is used to make swap_{read,write}page() go through the filesystem, and it's only used for swap files over NFS. So, !SWP_FS means non NFS for now, it could be either file backed or device backed. Something similar goes with legacy SWP_FILE.

So in order to achieve the goal of the original patch, SWP_BLKDEV should be used instead.

FS corruption can be observed with SSD device + XFS + fragmented swapfile due to CONFIG_THP_SWAP=y.

I reproduced the issue with the following details:

Environment: QEMU + upstream kernel + buildroot + NVMe (2 GB)

Kernel config: CONFIG_BLK_DEV_NVME=y CONFIG_THP_SWAP=y

Some reproducable steps: mkfs.xfs -f /dev/nvme0n1 mkdir /tmp/mnt mount /dev/nvme0n1 /tmp/mnt bs="32k" sz="1024m" # doesn't matter too much, I also tried 16m xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw xfs_io -f -c "pwrite -F -S 0 -b $bs 0 $sz" -c "fdatasync" /tmp/mnt/sw xfs_io -f -c "pwrite -R -b $bs 0 $sz" -c "fsync" /tmp/mnt/sw

mkswap /tmp/mnt/sw swapon /tmp/mnt/sw

stress --vm 2 --vm-bytes 600M # doesn't matter too much as well

Symptoms: - FS corruption (e.g. checksum failure) - memory corruption at: 0xd2808010 - segfault

Link: https://lkml.kernel.org/r/20200820045323.7809-1-hsiangkao@redhat.com Fixes: f0eea189e8e9 ("mm, THP, swap: Don't allocate huge cluster for file backed swap device") Fixes: 38d8b4e6bdc8 ("mm, THP, swap: delay splitting THP during swap out") Signed-off-by: Gao Xiang hsiangkao@redhat.com Reviewed-by: "Huang, Ying" ying.huang@intel.com Reviewed-by: Yang Shi shy828301@gmail.com Acked-by: Rafael Aquini aquini@redhat.com Cc: Matthew Wilcox willy@infradead.org Cc: Carlos Maiolino cmaiolino@redhat.com Cc: Eric Sandeen esandeen@redhat.com Cc: Dave Chinner david@fromorbit.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/swapfile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/swapfile.c~mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake +++ a/mm/swapfile.c @@ -1078,7 +1078,7 @@ start_over: goto nextsi; } if (size == SWAPFILE_CLUSTER) { - if (!(si->flags & SWP_FS)) + if (si->flags & SWP_BLKDEV) n_ret = swap_alloc_cluster(si, swp_entries); } else n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE, _