KASAN: user-memory-access Read in put_page

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    bef7b2a7 Merge tag 'devicetree-for-5.7' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16940efbe00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f72ba8a207627d60
dashboard link: https://syzkaller.appspot.com/bug?extid=b4501d3e966ff59f6090
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15d79efbe00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1705901be00000

The bug was bisected to:

commit 4426e945df588f2878affddf88a51259200f7e29
Author: Peter Xu <peterx@xxxxxxxxxx>
Date:   Thu Apr 2 04:08:49 2020 +0000

    mm/gup: allow VM_FAULT_RETRY for multiple times

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1441b1fbe00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1641b1fbe00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1241b1fbe00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b4501d3e966ff59f6090@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")

==================================================================
BUG: KASAN: user-memory-access in atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: user-memory-access in page_ref_count include/linux/page_ref.h:67 [inline]
BUG: KASAN: user-memory-access in put_page_testzero include/linux/mm.h:675 [inline]
BUG: KASAN: user-memory-access in put_page+0x110/0x1d0 include/linux/mm.h:1136
Read of size 4 at addr 00003fbf7e8680b0 by task syz-executor574/7201

CPU: 0 PID: 7201 Comm: syz-executor574 Not tainted 5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 __kasan_report+0x122/0x190 mm/kasan/report.c:507
 kasan_report+0x4d/0x80 mm/kasan/common.c:648
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 7201 Comm: syz-executor574 Tainted: G    B             5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 panic+0x264/0x7a0 kernel/panic.c:221
 end_report mm/kasan/report.c:96 [inline]
 __kasan_report+0x187/0x190 mm/kasan/report.c:510
 kasan_report+0x4d/0x80 mm/kasan/common.c:648
Kernel Offset: disabled
Rebooting in 86400 seconds..


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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
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