lockdep reports possible recursive locking for sb_writers from do_iter_write and do_sendfile

[Andrei Vagin]

Hello,

We run CRIU tests for Linus' tree and today we found this warning:

[   27.131931] ============================================
[   27.132008] WARNING: possible recursive locking detected
[   27.132085] 4.12.0+ #1 Not tainted
[   27.132158] --------------------------------------------
[   27.132243] criu/1537 is trying to acquire lock:
[   27.132330]  (sb_writers#5){.+.+.+}, at: [<ffffffffac3af8a4>]
do_iter_write+0x1d4/0x390
[   27.132429]
[   27.132429] but task is already holding lock:
[   27.132511]  (sb_writers#5){.+.+.+}, at: [<ffffffffac3b0861>] +0x671/0x6e0
[   27.132594]
[   27.132594] other info that might help us debug this:
[   27.132671]  Possible unsafe locking scenario:
[   27.132671]
[   27.132747]        CPU0
[   27.132819]        ----
[   27.132892]   lock(sb_writers#5);
[   27.132972]   lock(sb_writers#5);
[   27.133056]
[   27.133056]  *** DEADLOCK ***
[   27.133056]
[   27.133154]  May be due to missing lock nesting notation
[   27.133154]
[   27.133245] 1 lock held by criu/1537:
[   27.133325]  #0:  (sb_writers#5){.+.+.+}, at: [<ffffffffac3b0861>]
do_sendfile+0x671/0x6e0
[   27.133424]
[   27.133424] stack backtrace:
[   27.133515] CPU: 0 PID: 1537 Comm: criu Not tainted 4.12.0+ #1
[   27.133598] Hardware name: Google Google Compute Engine/Google
Compute Engine, BIOS Google 01/01/2011
[   27.133690] Call Trace:
[   27.133774]  dump_stack+0x85/0xc2
[   27.133859]  __lock_acquire+0x1dbc/0x1e70
[   27.133949]  ? debug_check_no_locks_freed+0x1c0/0x1c0
[   27.134034]  ? do_splice_direct+0x113/0x160
[   27.134117]  ? do_sendfile+0x37e/0x6e0
[   27.134199]  ? SyS_sendfile64+0x122/0x130
[   27.134282]  ? entry_SYSCALL_64_fastpath+0x23/0xc2
[   27.134367]  ? find_held_lock+0x119/0x150
[   27.134456]  ? __lock_is_held+0x93/0x100
[   27.134539]  ? current_time+0x18/0x80
[   27.134623]  lock_acquire+0x101/0x220
[   27.134706]  ? lock_acquire+0x101/0x220
[   27.134791]  ? do_iter_write+0x1d4/0x390
[   27.134895]  __sb_start_write+0xc6/0x1e0
[   27.134998]  ? do_iter_write+0x1d4/0x390
[   27.135082]  do_iter_write+0x1d4/0x390
[   27.135167]  ? kasan_unpoison_shadow+0x36/0x50
[   27.135256]  ? kasan_kmalloc+0xad/0xe0
[   27.135346]  vfs_iter_write+0x4e/0x70
[   27.135430]  iter_file_splice_write+0x409/0x650
[   27.135515]  ? page_cache_pipe_buf_steal+0x140/0x140
[   27.135599]  ? mark_held_locks+0x8e/0xc0
[   27.135686]  ? common_file_perm+0xe6/0x2c0
[   27.135769]  ? trace_hardirqs_on_caller+0x18b/0x270
[   27.135853]  ? __fsnotify_parent+0x2c/0x130
[   27.135942]  ? rw_verify_area+0x78/0x140
[   27.136026]  direct_splice_actor+0x94/0xb0
[   27.136110]  splice_direct_to_actor+0x1b9/0x400
[   27.136194]  ? generic_pipe_buf_nosteal+0x10/0x10
[   27.136278]  ? do_splice_to+0xc0/0xc0
[   27.136362]  ? rw_verify_area+0x78/0x140
[   27.136446]  do_splice_direct+0x113/0x160
[   27.136537]  ? splice_direct_to_actor+0x400/0x400
[   27.136621]  ? __sb_start_write+0xed/0x1e0
[   27.136704]  ? do_sendfile+0x671/0x6e0
[   27.136788]  ? __fget_light+0xa7/0xc0
[   27.136872]  do_sendfile+0x37e/0x6e0
[   27.136961]  ? do_compat_pwritev64+0xa0/0xa0
[   27.137047]  ? ext4_find_unwritten_pgoff.isra.14+0x480/0x480
[   27.137132]  ? vfs_read+0x15d/0x1d0
[   27.137215]  SyS_sendfile64+0x122/0x130
[   27.137297]  ? SyS_sendfile+0x120/0x120
[   27.137385]  ? trace_hardirqs_on_caller+0x18b/0x270
[   27.137469]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[   27.137554]  entry_SYSCALL_64_fastpath+0x23/0xc2
[   27.137638] RIP: 0033:0x7f2bb27e8f5a
[   27.137720] RSP: 002b:00007ffc53a398d8 EFLAGS: 00000206 ORIG_RAX:
0000000000000028
[   27.137813] RAX: ffffffffffffffda RBX: ffffffffac168175 RCX: 00007f2bb27e8f5a
[   27.137897] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
[   27.137985] RBP: ffff8801c8547f98 R08: 00000000004af768 R09: ffffffffffffe6f0
[   27.138069] R10: 00000000000059a8 R11: 0000000000000206 R12: 0000000001e49f00
[   27.138152] R13: 00007f2bb33081e0 R14: 000000000000000b R15: 0000000000000001
[   27.138243]  ? trace_hardirqs_off_caller+0xc5/0x110

$ git describe origin/master
v4.12-7934-g9f45efb

Here is all logs: https://goo.gl/TK6VSy

Thanks.
Andrei