syzkaller reports the following issue:

BUG: unable to handle page fault for address: ffff888021f7e005
PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e79 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64
Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01
RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb
RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005
RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005
R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005
R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb
FS:  00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 zero_user_segments include/linux/highmem.h:272 [inline]
 folio_zero_range include/linux/highmem.h:428 [inline]
 truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237
 truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381
 truncate_inode_pages mm/truncate.c:452 [inline]
 truncate_pagecache+0x63/0x90 mm/truncate.c:753
 simple_setattr+0xed/0x110 fs/libfs.c:535
 secretmem_setattr+0xae/0xf0 mm/secretmem.c:170
 notify_change+0xb8c/0x12b0 fs/attr.c:424
 do_truncate+0x13c/0x200 fs/open.c:65
 do_sys_ftruncate+0x536/0x730 fs/open.c:193
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7fb29d900899
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899
RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003
RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c
R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000
 </TASK>
Modules linked in:
CR2: ffff888021f7e005
---[ end trace 0000000000000000 ]---

Eric Biggers suggested that this happens when
secretmem_setattr()->simple_setattr() races with secretmem_fault() so that
a page that is faulted in by secretmem_fault() (and thus removed from the
direct map) is zeroed by inode truncation right afterwards.

Use mapping->invalidate_lock to make secretmem_fault() and
secretmem_setattr() mutually exclusive.

[rppt@linux.ibm.com: v3]
  Link: https://lkml.kernel.org/r/20220714091337.412297-1-rppt@kernel.org
Link: https://lkml.kernel.org/r/20220707165650.248088-1-rppt@kernel.org
Reported-by: syzbot+9bd2b7adbd34b30b87e4@syzkaller.appspotmail.com
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>