BUG: unable to handle kernel paging request in rb_erase

[syzbot <syzbot+0e37e9d19bded16b8ab9@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    9b1f2cbd Merge tag 'clk-fixes-for-linus' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15dfdeaa100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c14212794ed9ad24
dashboard link: https://syzkaller.appspot.com/bug?extid=0e37e9d19bded16b8ab9
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0e37e9d19bded16b8ab9@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: ffff887ffffffff0
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8682 Comm: syz-executor.3 Not tainted 5.7.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__rb_erase_augmented include/linux/rbtree_augmented.h:201 [inline]
RIP: 0010:rb_erase+0x37/0x18d0 lib/rbtree.c:443
Code: 89 f7 41 56 41 55 49 89 fd 48 83 c7 08 48 89 fa 41 54 48 c1 ea 03 55 53 48 83 ec 18 80 3c 02 00 0f 85 89 10 00 00 49 8d 7d 10 <4d> 8b 75 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80
RSP: 0018:ffffc900178ffb58 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8880354d0000 RCX: ffffc9000fb6d000
RDX: 1ffff10ffffffffe RSI: ffff88800011dfe0 RDI: ffff887ffffffff8
RBP: ffff887fffffffb0 R08: ffff888057284280 R09: fffffbfff185d12e
R10: ffffffff8c2e896f R11: fffffbfff185d12d R12: ffff88800011dfe0
R13: ffff887fffffffe8 R14: 000000000001dfe0 R15: ffff88800011dfe0
FS:  00007fa002d21700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff887ffffffff0 CR3: 00000000a2164000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 nfsd_reply_cache_free_locked+0x198/0x380 fs/nfsd/nfscache.c:127
 nfsd_reply_cache_shutdown+0x150/0x350 fs/nfsd/nfscache.c:203
 nfsd_exit_net+0x189/0x4c0 fs/nfsd/nfsctl.c:1504
 ops_exit_list.isra.0+0xa8/0x150 net/core/net_namespace.c:186
 setup_net+0x50c/0x860 net/core/net_namespace.c:364
 copy_net_ns+0x293/0x590 net/core/net_namespace.c:482
 create_new_namespaces+0x3fb/0xb30 kernel/nsproxy.c:108
 unshare_nsproxy_namespaces+0xbd/0x1f0 kernel/nsproxy.c:229
 ksys_unshare+0x43d/0x8e0 kernel/fork.c:2970
 __do_sys_unshare kernel/fork.c:3038 [inline]
 __se_sys_unshare kernel/fork.c:3036 [inline]
 __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3036
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45ca29
Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fa002d20c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 000000000050a1c0 RCX: 000000000045ca29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040000000
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000c4e R14: 00000000004ce9bd R15: 00007fa002d216d4
Modules linked in:
CR2: ffff887ffffffff0
---[ end trace f929dcba0362906a ]---
RIP: 0010:__rb_erase_augmented include/linux/rbtree_augmented.h:201 [inline]
RIP: 0010:rb_erase+0x37/0x18d0 lib/rbtree.c:443
Code: 89 f7 41 56 41 55 49 89 fd 48 83 c7 08 48 89 fa 41 54 48 c1 ea 03 55 53 48 83 ec 18 80 3c 02 00 0f 85 89 10 00 00 49 8d 7d 10 <4d> 8b 75 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80
RSP: 0018:ffffc900178ffb58 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8880354d0000 RCX: ffffc9000fb6d000
RDX: 1ffff10ffffffffe RSI: ffff88800011dfe0 RDI: ffff887ffffffff8
RBP: ffff887fffffffb0 R08: ffff888057284280 R09: fffffbfff185d12e
R10: ffffffff8c2e896f R11: fffffbfff185d12d R12: ffff88800011dfe0
R13: ffff887fffffffe8 R14: 000000000001dfe0 R15: ffff88800011dfe0
FS:  00007fa002d21700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff887ffffffff0 CR3: 00000000a2164000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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