[syzbot] WARNING: suspicious RCU usage in copy_pte_range

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1e43c377 Merge tag 'xtensa-20210329' of git://github.com/j..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15604986d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=71a75beb62b62a34
dashboard link: https://syzkaller.appspot.com/bug?extid=c2d2a6e2af34adb88749
compiler:       Debian clang version 11.0.1-2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c2d2a6e2af34adb88749@xxxxxxxxxxxxxxxxxxxxxxxxx

=============================
WARNING: suspicious RCU usage
5.12.0-rc5-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:8294 Illegal context switch in RCU-sched read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
3 locks held by syz-executor.2/8400:
 #0: ffffffff8c796770 (dup_mmap_sem){.+.+}-{0:0}, at: dup_mmap+0x73/0xde0 kernel/fork.c:479
 #1: ffff8880286c0158 (&mm->mmap_lock#2){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff8880286c0158 (&mm->mmap_lock#2){++++}-{3:3}, at: dup_mmap+0x87/0xde0 kernel/fork.c:480
 #2: ffff8880286c2458 (&mm->mmap_lock/1){+.+.}-{3:3}, at: mmap_write_lock_nested include/linux/mmap_lock.h:78 [inline]
 #2: ffff8880286c2458 (&mm->mmap_lock/1){+.+.}-{3:3}, at: dup_mmap+0xd1/0xde0 kernel/fork.c:489

stack backtrace:
CPU: 1 PID: 8400 Comm: syz-executor.2 Not tainted 5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x176/0x24e lib/dump_stack.c:120
 ___might_sleep+0xb4/0x530 kernel/sched/core.c:8294
 copy_pte_range+0x255b/0x2a20 mm/memory.c:1010
 copy_pmd_range mm/memory.c:1064 [inline]
 copy_pud_range mm/memory.c:1101 [inline]
 copy_p4d_range mm/memory.c:1125 [inline]
 copy_page_range+0xba9/0xff0 mm/memory.c:1198
 dup_mmap+0x9aa/0xde0 kernel/fork.c:594
 dup_mm+0x8c/0x310 kernel/fork.c:1368
 copy_mm kernel/fork.c:1424 [inline]
 copy_process+0x24c1/0x5690 kernel/fork.c:2113
 kernel_clone+0x1a6/0x6c0 kernel/fork.c:2500
 __do_sys_clone kernel/fork.c:2617 [inline]
 __se_sys_clone kernel/fork.c:2601 [inline]
 __x64_sys_clone+0x1d5/0x220 kernel/fork.c:2601
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x464a4b
Code: ed 0f 85 60 01 00 00 64 4c 8b 0c 25 10 00 00 00 45 31 c0 4d 8d 91 d0 02 00 00 31 d2 31 f6 bf 11 00 20 01 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 89 00 00 00 41 89 c5 85 c0 0f 85 90 00 00
RSP: 002b:00007ffc64260880 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000464a4b
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000003070400
R10: 00000000030706d0 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000001 R15: 00007ffc64260970


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