[syzbot] WARNING: suspicious RCU usage in mas_walk

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bdc61aad77fa Add linux-next specific files for 20220428
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15bb3dc2f00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=87767e89da13a759
dashboard link: https://syzkaller.appspot.com/bug?extid=2ee18845e89ae76342c5
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1118a5f6f00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=125bd212f00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2ee18845e89ae76342c5@xxxxxxxxxxxxxxxxxxxxxxxxx

=============================
WARNING: suspicious RCU usage
5.18.0-rc4-next-20220428-syzkaller #0 Not tainted
-----------------------------
lib/maple_tree.c:844 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
5 locks held by syz-executor842/4211:
 #0: ffff88807f0ae460 (sb_writers#8){.+.+}-{0:0}, at: ksys_write+0x127/0x250 fs/read_write.c:644
 #1: ffff88801df04488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x28c/0x610 fs/kernfs/file.c:282
 #2: ffff8881453b9a00 (kn->active#106){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b0/0x610 fs/kernfs/file.c:283
 #3: ffffffff8bedc528 (ksm_thread_mutex){+.+.}-{3:3}, at: run_store+0xd1/0xa60 mm/ksm.c:2917
 #4: ffff88801e5e8fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_read_lock include/linux/mmap_lock.h:117 [inline]
 #4: ffff88801e5e8fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: unmerge_and_remove_all_rmap_items mm/ksm.c:989 [inline]
 #4: ffff88801e5e8fd8 (&mm->mmap_lock#2){++++}-{3:3}, at: run_store+0x2a5/0xa60 mm/ksm.c:2923

stack backtrace:
CPU: 0 PID: 4211 Comm: syz-executor842 Not tainted 5.18.0-rc4-next-20220428-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 mas_root lib/maple_tree.c:844 [inline]
 mas_start lib/maple_tree.c:1331 [inline]
 mas_state_walk lib/maple_tree.c:3745 [inline]
 mas_walk+0x45e/0x670 lib/maple_tree.c:4923
 mas_find+0x442/0xc90 lib/maple_tree.c:5861
 vma_find include/linux/mm.h:664 [inline]
 vma_next include/linux/mm.h:673 [inline]
 unmerge_and_remove_all_rmap_items mm/ksm.c:990 [inline]
 run_store+0x2ed/0xa60 mm/ksm.c:2923
 kobj_attr_store+0x50/0x80 lib/kobject.c:824
 sysfs_kf_write+0x110/0x160 fs/sysfs/file.c:136
 kernfs_fop_write_iter+0x3f8/0x610 fs/kernfs/file.c:291
 call_write_iter include/linux/fs.h:2059 [inline]
 new_sync_write+0x38a/0x560 fs/read_write.c:504
 vfs_write+0x7c0/0xac0 fs/read_write.c:591
 ksys_write+0x127/0x250 fs/read_write.c:644
 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+0x44/0xae
RIP: 0033:0x7f6a91306e79
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffddeb8cde8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000000f4240 RCX: 00007f6a91306e79
RDX: 0000000000000002 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000020117000 R11: 0000000000000246 R12: 000000000000cf84
R13: 00007ffddeb8cdfc R14: 00007ffddeb8ce10 R15: 00007ffddeb8ce00
 </TASK>


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