============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz-executor255/5609 is trying to acquire lock:
ffff8880446a23e0 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
ffff8880446a23e0 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: lookup_slow+0x46/0x70 fs/namei.c:1935

but task is already holding lock:
ffff8880446a2990 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff8880446a2990 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: cache_write+0x7b/0x210 net/sunrpc/cache.c:961

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

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#11);
  lock(&sb->s_type->i_mutex_key#11);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

locks held by syz-executor255/5609: 2, last CPU#0:
 #0: ffff8880371ca510 (sb_writers#3){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline]
 #0: ffff8880371ca510 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #1: ffff8880446a2990 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #1: ffff8880446a2990 (&sb->s_type->i_mutex_key#11){++++}-{4:4}, at: cache_write+0x7b/0x210 net/sunrpc/cache.c:961

stack backtrace:
CPU: 0 UID: 0 PID: 5609 Comm: syz-executor255 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x27a/0x290 kernel/locking/lockdep.c:3057
 check_deadlock kernel/locking/lockdep.c:3109 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x261c/0x2e40 kernel/locking/lockdep.c:5254
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
 down_read+0x97/0x200 kernel/locking/rwsem.c:1574
 inode_lock_shared include/linux/fs.h:1039 [inline]
 lookup_slow+0x46/0x70 fs/namei.c:1935
 walk_component fs/namei.c:2282 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x3f5/0x8c0 fs/namei.c:2813
 filename_lookup+0x265/0x5d0 fs/namei.c:2842
 kern_path+0x3d/0x150 fs/namei.c:3036
 svc_export_parse+0x237/0xa90 fs/nfsd/export.c:1341
 cache_do_downcall net/sunrpc/cache.c:922 [inline]
 cache_downcall net/sunrpc/cache.c:944 [inline]
 cache_write+0x194/0x210 net/sunrpc/cache.c:962
 pde_write fs/proc/inode.c:330 [inline]
 proc_reg_write+0x1f6/0x2f0 fs/proc/inode.c:342
 vfs_write+0x29f/0xbb0 fs/read_write.c:685
 ksys_write+0x156/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd4f92f3649
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffca6d23698 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 645f636f72702f2e RCX: 00007fd4f92f3649
RDX: 0000000000000025 RSI: 0000200000000b00 RDI: 0000000000000004
RBP: 0000000000000001 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000006 R11: 0000000000000246 R12: 00007ffca6d23808
R13: 431bde82d7b634db R14: 00007fd4f9386c40 R15: 0000000000000002
 </TASK>