From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: [patch 03/10] page-flags: fix a crash at
 SetPageError(THP_SWAP)
Date: Sat, 21 Mar 2020 18:22:17 -0700
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From: Qian Cai <cai@lca.pw>
Subject: page-flags: fix a crash at SetPageError(THP_SWAP)

The commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after swapped
out") supported writing THP to a swap device but forgot to upgrade an
older commit df8c94d13c7e ("page-flags: define behavior of FS/IO-related
flags on compound pages") which could trigger a crash during THP swapping
out with DEBUG_VM_PGFLAGS=y,

kernel BUG at include/linux/page-flags.h:317!

page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
page:fffff3b2ec3a8000 refcount:512 mapcount:0 mapping:000000009eb0338c
index:0x7f6e58200 head:fffff3b2ec3a8000 order:9 compound_mapcount:0
compound_pincount:0
anon flags:
0x45fffe0000d8454(uptodate|lru|workingset|owner_priv_1|writeback|head|reclaim|swapbacked)

end_swap_bio_write()
  SetPageError(page)
    VM_BUG_ON_PAGE(1 && PageCompound(page))

<IRQ>
bio_endio+0x297/0x560
dec_pending+0x218/0x430 [dm_mod]
clone_endio+0xe4/0x2c0 [dm_mod]
bio_endio+0x297/0x560
blk_update_request+0x201/0x920
scsi_end_request+0x6b/0x4b0
scsi_io_completion+0x509/0x7e0
scsi_finish_command+0x1ed/0x2a0
scsi_softirq_done+0x1c9/0x1d0
__blk_mqnterrupt+0xf/0x20
</IRQ>

Fix by checking PF_NO_TAIL in those places instead.

Link: http://lkml.kernel.org/r/20200310235846.1319-1-cai@lca.pw
Fixes: bd4c82c22c36 ("mm, THP, swap: delay splitting THP after swapped out")
Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Rafael Aquini <aquini@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/page-flags.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/page-flags.h~page-flags-fix-a-crash-at-setpageerrorthp_swap
+++ a/include/linux/page-flags.h
@@ -311,7 +311,7 @@ static inline int TestClearPage##uname(s
 
 __PAGEFLAG(Locked, locked, PF_NO_TAIL)
 PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
-PAGEFLAG(Error, error, PF_NO_COMPOUND) TESTCLEARFLAG(Error, error, PF_NO_COMPOUND)
+PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
 PAGEFLAG(Referenced, referenced, PF_HEAD)
 	TESTCLEARFLAG(Referenced, referenced, PF_HEAD)
 	__SETPAGEFLAG(Referenced, referenced, PF_HEAD)
_