============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.17/4316 is trying to acquire lock:
ffff8880170af728 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:797 [inline]
ffff8880170af728 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: lookup_slow+0x46/0x70 fs/namei.c:1687

but task is already holding lock:
ffff8880170af1d0 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
ffff8880170af1d0 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: cache_write+0x75/0x1e0 net/sunrpc/cache.c:942

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#10);
  lock(&sb->s_type->i_mutex_key#10);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.0.17/4316:
 #0: ffff888026112460 (sb_writers#4){.+.+}-{0:0}, at: vfs_write+0x296/0xd70 fs/read_write.c:590
 #1: ffff8880170af1d0 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
 #1: ffff8880170af1d0 (&sb->s_type->i_mutex_key#10){++++}-{3:3}, at: cache_write+0x75/0x1e0 net/sunrpc/cache.c:942

stack backtrace:
CPU: 1 PID: 4316 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 __lock_acquire+0x1247/0x7b50 kernel/locking/lockdep.c:-1
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
 down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
 inode_lock_shared include/linux/fs.h:797 [inline]
 lookup_slow+0x46/0x70 fs/namei.c:1687
 walk_component+0x314/0x460 fs/namei.c:1984
 lookup_last fs/namei.c:2439 [inline]
 path_lookupat+0x148/0x420 fs/namei.c:2463
 filename_lookup+0x21e/0x550 fs/namei.c:2492
 kern_path+0x37/0x190 fs/namei.c:2590
 svc_export_parse+0x22d/0x9c0 fs/nfsd/export.c:609
 cache_do_downcall net/sunrpc/cache.c:903 [inline]
 cache_downcall net/sunrpc/cache.c:925 [inline]
 cache_write+0x180/0x1e0 net/sunrpc/cache.c:943
 pde_write fs/proc/inode.c:335 [inline]
 proc_reg_write+0x1dd/0x2c0 fs/proc/inode.c:347
 vfs_write+0x304/0xd70 fs/read_write.c:592
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f51a57ce0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdd8fbdb58 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f51a5a55fa0 RCX: 00007f51a57ce0d9
RDX: 0000000000000025 RSI: 0000200000000b00 RDI: 0000000000000004
RBP: 00007f51a5865024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f51a5a55fac R14: 00007f51a5a55fa0 R15: 00007f51a5a55fa0
 </TASK>