linux-kernel - [PATCH 4.19 239/245] mm, THP, swap: fix allocating cluster for swapfile by mistake

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Message-Id: <20200929105958.626004366@linuxfoundation.org>
Date:   Tue, 29 Sep 2020 13:01:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Gao Xiang <hsiangkao@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Huang, Ying" <ying.huang@...el.com>,
        Yang Shi <shy828301@...il.com>,
        Rafael Aquini <aquini@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        Eric Sandeen <esandeen@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 239/245] mm, THP, swap: fix allocating cluster for swapfile by mistake

From: Gao Xiang <hsiangkao@...hat.com>

commit 41663430588c737dd735bad5a0d1ba325dcabd59 upstream.

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 reproducible 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

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@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
Acked-by: Rafael Aquini <aquini@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Carlos Maiolino <cmaiolino@...hat.com>
Cc: Eric Sandeen <esandeen@...hat.com>
Cc: Dave Chinner <david@...morbit.com>
Cc: <stable@...r.kernel.org>
Link: https://lkml.kernel.org/r/20200820045323.7809-1-hsiangkao@redhat.com
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -998,7 +998,7 @@ start_over:
 			goto nextsi;
 		}
 		if (size == SWAPFILE_CLUSTER) {
-			if (!(si->flags & SWP_FILE))
+			if (si->flags & SWP_BLKDEV)
 				n_ret = swap_alloc_cluster(si, swp_entries);
 		} else
 			n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,