+ mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake.patch added to -mm tree

* + mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake.patch added to -mm tree
@ 2020-08-20 21:21 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2020-08-20 21:21 UTC (permalink / raw)
  To: aquini, cmaiolino, esandeen, hsiangkao, mm-commits, shy828301,
	stable, willy, ying.huang


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-for-swapfile-by-mistake.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-swap-fix-allocating-cluster-for-swapfile-by-mistake.patch

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------------------------------------------------------
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: <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


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