The patch titled Subject: mm, THP, swap: fix allocating cluster for swapfile by mistake has been added to the -mm tree. Its filename is mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-swap-fix-allocating-cluster... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-swap-fix-allocating-cluster...

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated there every 3-4 working days

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

SWP_FS doesn't mean the device is file-backed swap device, which just means each writeback request should go through fs by DIO. Or it'll just use extents added by .swap_activate(), but it also works as file-backed swap device.

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/20200819195613.24269-1-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 Cc: "Huang, Ying" ying.huang@intel.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, _

Patches currently in -mm which might be from hsiangkao@redhat.com are

mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake.patch