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* Boot warning at rcu_check_gp_start_stall()
@ 2020-01-21  4:25 Qian Cai
  2020-01-21  5:09 ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-21  4:25 UTC (permalink / raw)
  To: Paul E. McKenney; +Cc: rcu, LKML

Booting a server generates this warning on linux-next with this config,

https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config

Does it ring any bell?

[   96.714534] 0xffffffffff800000-0x0000000000000000           8M                               pmd
[   96.872278] Dentry cache hash table entries: 8388608 (order: 14, 67108864 bytes, vmalloc)
[   96.938599] Inode-cache hash table entries: 4194304 (order: 13, 33554432 bytes, vmalloc)
[   96.955357] Mount-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
[   96.965514] Mountpoint-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
[   96.994553] ------------[ cut here ]------------
[   96.999922] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_stall.h:672 rcu_check_gp_start_stall.isra.67+0x1ae/0x260
[   97.004526] Modules linked in:
[   97.004526] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G    B             5.5.0-rc6-next-20200120+ #1
[   97.004526] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
[   97.004526] RIP: 0010:rcu_check_gp_start_stall.isra.67+0x1ae/0x260
[   97.004526] Code: 61 01 4c 01 e6 48 39 f2 78 58 be 04 00 00 00 48 c7 c7 e0 24 b7 85 e8 71 0f 25 00 b8 01 00 00 00 87 05 66 32 7b 04 85 c0 75 2f <0f> 0b 48 81 fb 40 13 9d 82 74 0c 48 c7 c7 40 13 9d 82 e8 2b 2a 8d
[   97.004526] RSP: 0000:ffffc90000007e18 EFLAGS: 00010046
[   97.004526] RAX: 0000000000000000 RBX: ffffffff829d1700 RCX: ffffffff813bf26f
[   97.004526] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff85b724e0
[   97.004526] RBP: ffffc90000007e30 R08: fffffbfff0b6e49d R09: fffffbfff0b6e49d
[   97.004526] R10: fffffbfff0b6e49c R11: ffffffff85b724e3 R12: 0000000000001964
[   97.004526] R13: 0000000000000246 R14: ffff888843045050 R15: ffff888843045018
[   97.004526] FS:  0000000000000000(0000) GS:ffff888843000000(0000) knlGS:0000000000000000
[   97.004526] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   97.004526] CR2: ffff8890779ff000 CR3: 0000000b7d212000 CR4: 00000000000406b0
[   97.004526] Call Trace:
[   97.004526]  <IRQ>
[   97.004526]  rcu_core+0x22b/0xb80
[   97.004526]  ? debug_lockdep_rcu_enabled+0x11/0x60
[   97.004526]  ? call_timer_fn+0x4e0/0x4e0
[   97.004526]  ? rcu_note_context_switch+0x3b0/0x3b0
[   97.004526]  ? lock_downgrade+0x3c0/0x3c0
[   97.004526]  ? rwlock_bug.part.1+0x60/0x60
[   97.004526]  ? lockdep_hardirqs_on+0x16/0x2a0
[   97.004526]  rcu_core_si+0xe/0x10
[   97.004526]  __do_softirq+0x123/0x766
[   97.004526]  ? do_raw_spin_unlock+0xa8/0x140
[   97.004526]  irq_exit+0xd6/0xf0
[   97.004526]  do_IRQ+0xa3/0x1e0
[   97.004526]  common_interrupt+0xf/0xf
[   97.004526]  </IRQ>
[   97.004526] RIP: 0010:__asan_load8+0x0/0xa0
[   97.004526] Code: e8 03 0f b6 04 30 84 c0 74 c2 38 d0 0f 9e c0 84 c0 74 b9 ba 01 00 00 00 be 04 00 00 00 e8 c8 e3 ff ff 5d c3 66 0f 1f 44 00 00 <55> 48 89 e5 48 8b 4d 08 e9 a3 d3 9f 01 48 b8 00 00 00 00 00 00 00
[   97.004526] RSP: 0000:ffffffff82807af0 EFLAGS: 00000257 ORIG_RAX: ffffffffffffffcf
[   97.004526] RAX: ffffffff82f25840 RBX: ffffffff82f25840 RCX: 0000000000000028
[   97.004526] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff82f25840
[   97.004526] RBP: ffffffff82807b30 R08: 0000000000000000 R09: 0000000000000004
[   97.004526] R10: ffff8890313c98fc R11: ffff8890313c98ff R12: 0000000000000000
[   97.004526] R13: 0000000000000080 R14: 0000000000000028 R15: 0000000000000000
[   97.004526]  ? _find_next_bit.constprop.1+0x4a/0x100
[   97.004526]  find_next_bit+0x14/0x20
[   97.004526]  cpumask_next+0x35/0x40
[   97.004526]  pcpu_alloc+0x4bf/0xa40
[   97.004526]  __alloc_percpu+0x15/0x20
[   97.004526]  __percpu_init_rwsem+0x28/0xa0
[   97.004526]  alloc_super+0x164/0x530
[   97.004526]  sget_fc+0xb9/0x3a0
[   97.004526]  ? compare_single+0x10/0x10
[   97.004526]  ? ramfs_symlink+0xe0/0xe0
[   97.004526]  vfs_get_super+0x4e/0x1a0
[   97.004526]  ? vfs_parse_fs_string+0x110/0x110
[   97.004526]  get_tree_nodev+0x16/0x20
[   97.004526]  ramfs_get_tree+0x15/0x20
[   97.004526]  vfs_get_tree+0x54/0x150
[   97.004526]  fc_mount+0x14/0x60
[   97.004526]  vfs_kern_mount.part.13+0x61/0xa0
[   97.004526]  mnt_init+0x1b0/0x34a
[   97.004526]  ? set_mphash_entries+0xa2/0xa2
[   97.004526]  ? __percpu_counter_init+0x127/0x140
[   97.004526]  vfs_caches_init+0xda/0xe6
[   97.004526]  start_kernel+0x55d/0x5dc
[   97.004526]  ? thread_stack_cache_init+0xb/0xb
[   97.004526]  ? idt_setup_from_table+0xd9/0x130
[   97.004526]  x86_64_start_reservations+0x24/0x26
[   97.004526]  x86_64_start_kernel+0xf4/0xfb
[   97.004526]  secondary_startup_64+0xb6/0xc0
[   97.004526] irq event stamp: 16832
[   97.004526] hardirqs last  enabled at (16831): [<ffffffff812a8399>] switch_mm+0x49/0x60
[   97.004526] hardirqs last disabled at (16832): [<ffffffff82fc0b52>] efi_set_virtual_address_map+0x4a7/0x574
[   97.004526] softirqs last  enabled at (15286): [<ffffffff82000447>] __do_softirq+0x447/0x766
[   97.004526] softirqs last disabled at (15279): [<ffffffff812d3ac6>] irq_exit+0xd6/0xf0
[   97.004526] ---[ end trace 33b25e8237e68c3c ]---
[   97.004535] rcu: rcu_sched: wait state: RCU_GP_IDLE(0) ->state: 0x1ffff delta ->gp_activity 4294945934 ->gp_req_activity 8637 ->gp_wake_time 4294945934 ->gp_wake_seq 0 ->gp_seq -1200 ->gp_seq_needed -1196 ->gp_flags 0x1
[   97.014531] rcu:     rcu_node 0:127 ->gp_seq -1200 ->gp_seq_needed -1196
[   97.024538] rcu:     rcu_node 0:15 ->gp_seq -1200 ->gp_seq_needed -1196
[   97.034530] rcu:     cpu 1 ->gp_seq_needed 0
[   97.039268] rcu:     cpu 2 ->gp_seq_needed 0
[   97.044530] rcu:     cpu 3 ->gp_seq_needed 0
[   97.049268] rcu:     cpu 4 ->gp_seq_needed 0
[   97.054530] rcu:     cpu 5 ->gp_seq_needed 0
[   97.059268] rcu:     cpu 6 ->gp_seq_needed 0
[   97.064006] rcu:     cpu 7 ->gp_seq_needed 0
[   97.064530] rcu:     cpu 8 ->gp_seq_needed 0
[   97.069268] rcu:     cpu 9 ->gp_seq_needed 0
[   97.074530] rcu:     cpu 10 ->gp_seq_needed 0
[   97.079354] rcu:     cpu 11 ->gp_seq_needed 0
[   97.084531] rcu:     cpu 12 ->gp_seq_needed 0
[   97.089356] rcu:     cpu 13 ->gp_seq_needed 0
[   97.094530] rcu:     cpu 14 ->gp_seq_needed 0
[   97.099355] rcu:     cpu 15 ->gp_seq_needed 0
[   97.192987] LVT offset 2 assigned for vector 0xf4
[   97.194558] numa_add_cpu cpu 0 node 0: mask now 0
[   97.194563] Last level iTLB entries: 4KB 1024, 2MB 1024, 4MB 512

or this,

[   96.807008] Inode-cache hash table entries: 4194304 (order: 13, 33554432 bytes, vmalloc)
[   96.823729] Mount-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
[   96.827982] Mountpoint-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
[   96.866430] ------------[ cut here ]------------
[   96.871797] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_stall.h:672 rcu_check_gp_start_stall.isra.67+0x1ae/0x260
[   96.876402] Modules linked in:
[   96.876402] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G    B             5.5.0-rc6-next-20200120+ #1
[   96.876402] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
[   96.876402] RIP: 0010:rcu_check_gp_start_stall.isra.67+0x1ae/0x260
[   96.876402] Code: 61 01 4c 01 e6 48 39 f2 78 58 be 04 00 00 00 48 c7 c7 e0 24 f7 b3 e8 71 0f 25 00 b8 01 00 00 00 87 05 66 32 7b 04 85 c0 75 2f <0f> 0b 48 81 fb 40 13 dd b0 74 0c 48 c7 c7 40 13 dd b0 e8 8b 2b 8d
[   96.876402] RSP: 0000:ffffc90000007e18 EFLAGS: 00010046
[   96.876402] RAX: 0000000000000000 RBX: ffffffffb0dd1700 RCX: ffffffffaf7bf26f
[   96.876402] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffffb3f724e0
[   96.876402] RBP: ffffc90000007e30 R08: fffffbfff67ee49d R09: fffffbfff67ee49d
[   96.876402] R10: fffffbfff67ee49c R11: ffffffffb3f724e3 R12: 0000000000001964
[   96.876402] R13: 0000000000000246 R14: ffff888843045050 R15: ffff888843045018
[   96.876402] FS:  0000000000000000(0000) GS:ffff888843000000(0000) knlGS:0000000000000000
[   96.876402] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   96.876402] CR2: ffff8890779ff000 CR3: 0000000b2a012000 CR4: 00000000000406b0
[   96.876402] Call Trace:
[   96.876402]  <IRQ>
[   96.876402]  rcu_core+0x22b/0xb80
[   96.876402]  ? debug_lockdep_rcu_enabled+0x11/0x60
[   96.876402]  ? call_timer_fn+0x4e0/0x4e0
[   96.876402]  ? rcu_note_context_switch+0x3b0/0x3b0
[   96.876402]  ? lock_downgrade+0x3c0/0x3c0
[   96.876402]  ? rwlock_bug.part.1+0x60/0x60
[   96.876402]  ? lockdep_hardirqs_on+0x16/0x2a0
[   96.876402]  rcu_core_si+0xe/0x10
[   96.876402]  __do_softirq+0x123/0x766
[   96.876402]  ? do_raw_spin_unlock+0xa8/0x140
[   96.876402]  irq_exit+0xd6/0xf0
[   96.876402]  do_IRQ+0xa3/0x1e0
[   96.876402]  common_interrupt+0xf/0xf
[   96.876402]  </IRQ>
[   96.876402] RIP: 0010:_raw_spin_unlock_irqrestore+0x46/0x50
[   96.876402] Code: 6a 6f ff 4c 89 e7 e8 69 fb 6f ff f6 c7 02 75 13 53 9d e8 ad 4c 7f ff 65 ff 0d fe ef f8 4f 5b 41 5c 5d c3 e8 ec 4d 7f ff 53 9d <eb> eb 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 65 ff 05 db ef f8
[   96.876402] RSP: 0000:ffffffffb0c07ab0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffcf
[   96.876402] RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffffffffaf789c26
[   96.876402] RDX: 0000000000000007 RSI: dffffc0000000000 RDI: ffffffffb1329794
[   96.876402] RBP: ffffffffb0c07ac0 R08: fffffbfff626282a R09: fffffbfff626282a
[   96.876402] R10: fffffbfff6262829 R11: ffffffffb131414b R12: ffffffffb0f8a860
[   96.876402] R13: ffffffffb0f8a980 R14: ffffffffb982af38 R15: ffff888216688310
[   96.876402]  ? lockdep_hardirqs_on+0x16/0x2a0
[   96.876402]  create_object+0x4a2/0x540
[   96.876402]  kmemleak_alloc_percpu+0xbd/0x150
[   96.876402]  pcpu_alloc+0x50c/0xa40
[   96.876402]  __alloc_percpu+0x15/0x20
[   96.876402]  __percpu_init_rwsem+0x28/0xa0
[   96.876402]  alloc_super+0x1ac/0x530
[   96.876402]  sget_fc+0xb9/0x3a0
[   96.876402]  ? compare_single+0x10/0x10
[   96.876402]  ? ramfs_symlink+0xe0/0xe0
[   96.876402]  vfs_get_super+0x4e/0x1a0
[   96.876402]  ? vfs_parse_fs_string+0x110/0x110
[   96.876402]  get_tree_nodev+0x16/0x20
[   96.876402]  ramfs_get_tree+0x15/0x20
[   96.876402]  vfs_get_tree+0x54/0x150
[   96.876402]  fc_mount+0x14/0x60
[   96.876402]  vfs_kern_mount.part.13+0x61/0xa0
[   96.876402]  mnt_init+0x1b0/0x34a
[   96.876402]  ? set_mphash_entries+0xa2/0xa2
[   96.876402]  ? __percpu_counter_init+0x127/0x140
[   96.876402]  vfs_caches_init+0xda/0xe6
[   96.876402]  start_kernel+0x55d/0x5dc
[   96.876402]  ? thread_stack_cache_init+0xb/0xb
[   96.876402]  ? idt_setup_from_table+0xd9/0x130
[   96.876402]  x86_64_start_reservations+0x24/0x26
[   96.876402]  x86_64_start_kernel+0xf4/0xfb
[   96.876402]  secondary_startup_64+0xb6/0xc0
[   96.876402] irq event stamp: 16832
[   96.876402] hardirqs last  enabled at (16831): [<ffffffffaf6a8399>] switch_mm+0x49/0x60
[   96.876402] hardirqs last disabled at (16832): [<ffffffffb13c0b52>] efi_set_virtual_address_map+0x4a7/0x574
[   96.876402] softirqs last  enabled at (15278): [<ffffffffb0400447>] __do_softirq+0x447/0x766
[   96.876402] softirqs last disabled at (15271): [<ffffffffaf6d3ac6>] irq_exit+0xd6/0xf0
[   96.876402] ---[ end trace 8c99b667a2f37d07 ]---
[   96.876412] rcu: rcu_sched: wait state: RCU_GP_IDLE(0) ->state: 0x1ffff delta ->gp_activity 4294945938 ->gp_req_activity 8641 ->gp_wake_time 4294945938 ->gp_wake_seq 0 ->gp_seq -1200 ->gp_seq_needed -1196 ->gp_flags 0x1
[   96.886409] rcu:     rcu_node 0:127 ->gp_seq -1200 ->gp_seq_needed -1196
[   96.896408] rcu:     rcu_node 0:15 ->gp_seq -1200 ->gp_seq_needed -1196
[   96.906408] rcu:     cpu 1 ->gp_seq_needed 0
[   96.911146] rcu:     cpu 2 ->gp_seq_needed 0
[   96.916407] rcu:     cpu 3 ->gp_seq_needed 0
[   96.921145] rcu:     cpu 4 ->gp_seq_needed 0
[   96.926407] rcu:     cpu 5 ->gp_seq_needed 0
[   96.931145] rcu:     cpu 6 ->gp_seq_needed 0
[   96.936407] rcu:     cpu 7 ->gp_seq_needed 0
[   96.941145] rcu:     cpu 8 ->gp_seq_needed 0
[   96.946407] rcu:     cpu 9 ->gp_seq_needed 0
[   96.951145] rcu:     cpu 10 ->gp_seq_needed 0
[   96.956407] rcu:     cpu 11 ->gp_seq_needed 0
[   96.961231] rcu:     cpu 12 ->gp_seq_needed 0
[   96.966407] rcu:     cpu 13 ->gp_seq_needed 0
[   96.971231] rcu:     cpu 14 ->gp_seq_needed 0
[   96.976055] rcu:     cpu 15 ->gp_seq_needed 0
[   97.064605] LVT offset 2 assigned for vector 0xf4
[   97.066435] numa_add_cpu cpu 0 node 0: mask now 0
[   97.066440] Last level iTLB entries: 4KB 1024, 2MB 1024, 4MB 512

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21  4:25 Boot warning at rcu_check_gp_start_stall() Qian Cai
@ 2020-01-21  5:09 ` Paul E. McKenney
  2020-01-21 11:45   ` Qian Cai
  0 siblings, 1 reply; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-21  5:09 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Mon, Jan 20, 2020 at 11:25:41PM -0500, Qian Cai wrote:
> Booting a server generates this warning on linux-next with this config,
> 
> https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
> 
> Does it ring any bell?

This is what you get when a grace period has been requested, but does
not start within 21 seconds or so.  The "->state: 0x1ffff" is a new one
on me -- that normally happens only before RCU's grace-period kthread
has been spawned.  But by 97 seconds after boot, it should definitely
already be up and running.

Is the system responsive at this point?

Except...  Why is it taking 96 seconds for the system to get to the point
where it prints "Dentry cache hash table entries:"?  That happens at 0.139
seconds on my laptop.  And at about the same time on a much larger system.

I could easily imagine that all sorts of things would break when boot
takes that long.

Maybe it is best just put a "return" statement at the beginning of
rcu_check_gp_start_stall() in kernel/rcu/tree_stall.h and see what
else breaks?

							Thanx, Paul

> [   96.714534] 0xffffffffff800000-0x0000000000000000           8M                               pmd
> [   96.872278] Dentry cache hash table entries: 8388608 (order: 14, 67108864 bytes, vmalloc)
> [   96.938599] Inode-cache hash table entries: 4194304 (order: 13, 33554432 bytes, vmalloc)
> [   96.955357] Mount-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
> [   96.965514] Mountpoint-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
> [   96.994553] ------------[ cut here ]------------
> [   96.999922] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_stall.h:672 rcu_check_gp_start_stall.isra.67+0x1ae/0x260
> [   97.004526] Modules linked in:
> [   97.004526] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G    B             5.5.0-rc6-next-20200120+ #1
> [   97.004526] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
> [   97.004526] RIP: 0010:rcu_check_gp_start_stall.isra.67+0x1ae/0x260
> [   97.004526] Code: 61 01 4c 01 e6 48 39 f2 78 58 be 04 00 00 00 48 c7 c7 e0 24 b7 85 e8 71 0f 25 00 b8 01 00 00 00 87 05 66 32 7b 04 85 c0 75 2f <0f> 0b 48 81 fb 40 13 9d 82 74 0c 48 c7 c7 40 13 9d 82 e8 2b 2a 8d
> [   97.004526] RSP: 0000:ffffc90000007e18 EFLAGS: 00010046
> [   97.004526] RAX: 0000000000000000 RBX: ffffffff829d1700 RCX: ffffffff813bf26f
> [   97.004526] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff85b724e0
> [   97.004526] RBP: ffffc90000007e30 R08: fffffbfff0b6e49d R09: fffffbfff0b6e49d
> [   97.004526] R10: fffffbfff0b6e49c R11: ffffffff85b724e3 R12: 0000000000001964
> [   97.004526] R13: 0000000000000246 R14: ffff888843045050 R15: ffff888843045018
> [   97.004526] FS:  0000000000000000(0000) GS:ffff888843000000(0000) knlGS:0000000000000000
> [   97.004526] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   97.004526] CR2: ffff8890779ff000 CR3: 0000000b7d212000 CR4: 00000000000406b0
> [   97.004526] Call Trace:
> [   97.004526]  <IRQ>
> [   97.004526]  rcu_core+0x22b/0xb80
> [   97.004526]  ? debug_lockdep_rcu_enabled+0x11/0x60
> [   97.004526]  ? call_timer_fn+0x4e0/0x4e0
> [   97.004526]  ? rcu_note_context_switch+0x3b0/0x3b0
> [   97.004526]  ? lock_downgrade+0x3c0/0x3c0
> [   97.004526]  ? rwlock_bug.part.1+0x60/0x60
> [   97.004526]  ? lockdep_hardirqs_on+0x16/0x2a0
> [   97.004526]  rcu_core_si+0xe/0x10
> [   97.004526]  __do_softirq+0x123/0x766
> [   97.004526]  ? do_raw_spin_unlock+0xa8/0x140
> [   97.004526]  irq_exit+0xd6/0xf0
> [   97.004526]  do_IRQ+0xa3/0x1e0
> [   97.004526]  common_interrupt+0xf/0xf
> [   97.004526]  </IRQ>
> [   97.004526] RIP: 0010:__asan_load8+0x0/0xa0
> [   97.004526] Code: e8 03 0f b6 04 30 84 c0 74 c2 38 d0 0f 9e c0 84 c0 74 b9 ba 01 00 00 00 be 04 00 00 00 e8 c8 e3 ff ff 5d c3 66 0f 1f 44 00 00 <55> 48 89 e5 48 8b 4d 08 e9 a3 d3 9f 01 48 b8 00 00 00 00 00 00 00
> [   97.004526] RSP: 0000:ffffffff82807af0 EFLAGS: 00000257 ORIG_RAX: ffffffffffffffcf
> [   97.004526] RAX: ffffffff82f25840 RBX: ffffffff82f25840 RCX: 0000000000000028
> [   97.004526] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff82f25840
> [   97.004526] RBP: ffffffff82807b30 R08: 0000000000000000 R09: 0000000000000004
> [   97.004526] R10: ffff8890313c98fc R11: ffff8890313c98ff R12: 0000000000000000
> [   97.004526] R13: 0000000000000080 R14: 0000000000000028 R15: 0000000000000000
> [   97.004526]  ? _find_next_bit.constprop.1+0x4a/0x100
> [   97.004526]  find_next_bit+0x14/0x20
> [   97.004526]  cpumask_next+0x35/0x40
> [   97.004526]  pcpu_alloc+0x4bf/0xa40
> [   97.004526]  __alloc_percpu+0x15/0x20
> [   97.004526]  __percpu_init_rwsem+0x28/0xa0
> [   97.004526]  alloc_super+0x164/0x530
> [   97.004526]  sget_fc+0xb9/0x3a0
> [   97.004526]  ? compare_single+0x10/0x10
> [   97.004526]  ? ramfs_symlink+0xe0/0xe0
> [   97.004526]  vfs_get_super+0x4e/0x1a0
> [   97.004526]  ? vfs_parse_fs_string+0x110/0x110
> [   97.004526]  get_tree_nodev+0x16/0x20
> [   97.004526]  ramfs_get_tree+0x15/0x20
> [   97.004526]  vfs_get_tree+0x54/0x150
> [   97.004526]  fc_mount+0x14/0x60
> [   97.004526]  vfs_kern_mount.part.13+0x61/0xa0
> [   97.004526]  mnt_init+0x1b0/0x34a
> [   97.004526]  ? set_mphash_entries+0xa2/0xa2
> [   97.004526]  ? __percpu_counter_init+0x127/0x140
> [   97.004526]  vfs_caches_init+0xda/0xe6
> [   97.004526]  start_kernel+0x55d/0x5dc
> [   97.004526]  ? thread_stack_cache_init+0xb/0xb
> [   97.004526]  ? idt_setup_from_table+0xd9/0x130
> [   97.004526]  x86_64_start_reservations+0x24/0x26
> [   97.004526]  x86_64_start_kernel+0xf4/0xfb
> [   97.004526]  secondary_startup_64+0xb6/0xc0
> [   97.004526] irq event stamp: 16832
> [   97.004526] hardirqs last  enabled at (16831): [<ffffffff812a8399>] switch_mm+0x49/0x60
> [   97.004526] hardirqs last disabled at (16832): [<ffffffff82fc0b52>] efi_set_virtual_address_map+0x4a7/0x574
> [   97.004526] softirqs last  enabled at (15286): [<ffffffff82000447>] __do_softirq+0x447/0x766
> [   97.004526] softirqs last disabled at (15279): [<ffffffff812d3ac6>] irq_exit+0xd6/0xf0
> [   97.004526] ---[ end trace 33b25e8237e68c3c ]---
> [   97.004535] rcu: rcu_sched: wait state: RCU_GP_IDLE(0) ->state: 0x1ffff delta ->gp_activity 4294945934 ->gp_req_activity 8637 ->gp_wake_time 4294945934 ->gp_wake_seq 0 ->gp_seq -1200 ->gp_seq_needed -1196 ->gp_flags 0x1
> [   97.014531] rcu:     rcu_node 0:127 ->gp_seq -1200 ->gp_seq_needed -1196
> [   97.024538] rcu:     rcu_node 0:15 ->gp_seq -1200 ->gp_seq_needed -1196
> [   97.034530] rcu:     cpu 1 ->gp_seq_needed 0
> [   97.039268] rcu:     cpu 2 ->gp_seq_needed 0
> [   97.044530] rcu:     cpu 3 ->gp_seq_needed 0
> [   97.049268] rcu:     cpu 4 ->gp_seq_needed 0
> [   97.054530] rcu:     cpu 5 ->gp_seq_needed 0
> [   97.059268] rcu:     cpu 6 ->gp_seq_needed 0
> [   97.064006] rcu:     cpu 7 ->gp_seq_needed 0
> [   97.064530] rcu:     cpu 8 ->gp_seq_needed 0
> [   97.069268] rcu:     cpu 9 ->gp_seq_needed 0
> [   97.074530] rcu:     cpu 10 ->gp_seq_needed 0
> [   97.079354] rcu:     cpu 11 ->gp_seq_needed 0
> [   97.084531] rcu:     cpu 12 ->gp_seq_needed 0
> [   97.089356] rcu:     cpu 13 ->gp_seq_needed 0
> [   97.094530] rcu:     cpu 14 ->gp_seq_needed 0
> [   97.099355] rcu:     cpu 15 ->gp_seq_needed 0
> [   97.192987] LVT offset 2 assigned for vector 0xf4
> [   97.194558] numa_add_cpu cpu 0 node 0: mask now 0
> [   97.194563] Last level iTLB entries: 4KB 1024, 2MB 1024, 4MB 512
> 
> or this,
> 
> [   96.807008] Inode-cache hash table entries: 4194304 (order: 13, 33554432 bytes, vmalloc)
> [   96.823729] Mount-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
> [   96.827982] Mountpoint-cache hash table entries: 131072 (order: 8, 1048576 bytes, vmalloc)
> [   96.866430] ------------[ cut here ]------------
> [   96.871797] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_stall.h:672 rcu_check_gp_start_stall.isra.67+0x1ae/0x260
> [   96.876402] Modules linked in:
> [   96.876402] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G    B             5.5.0-rc6-next-20200120+ #1
> [   96.876402] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
> [   96.876402] RIP: 0010:rcu_check_gp_start_stall.isra.67+0x1ae/0x260
> [   96.876402] Code: 61 01 4c 01 e6 48 39 f2 78 58 be 04 00 00 00 48 c7 c7 e0 24 f7 b3 e8 71 0f 25 00 b8 01 00 00 00 87 05 66 32 7b 04 85 c0 75 2f <0f> 0b 48 81 fb 40 13 dd b0 74 0c 48 c7 c7 40 13 dd b0 e8 8b 2b 8d
> [   96.876402] RSP: 0000:ffffc90000007e18 EFLAGS: 00010046
> [   96.876402] RAX: 0000000000000000 RBX: ffffffffb0dd1700 RCX: ffffffffaf7bf26f
> [   96.876402] RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffffb3f724e0
> [   96.876402] RBP: ffffc90000007e30 R08: fffffbfff67ee49d R09: fffffbfff67ee49d
> [   96.876402] R10: fffffbfff67ee49c R11: ffffffffb3f724e3 R12: 0000000000001964
> [   96.876402] R13: 0000000000000246 R14: ffff888843045050 R15: ffff888843045018
> [   96.876402] FS:  0000000000000000(0000) GS:ffff888843000000(0000) knlGS:0000000000000000
> [   96.876402] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   96.876402] CR2: ffff8890779ff000 CR3: 0000000b2a012000 CR4: 00000000000406b0
> [   96.876402] Call Trace:
> [   96.876402]  <IRQ>
> [   96.876402]  rcu_core+0x22b/0xb80
> [   96.876402]  ? debug_lockdep_rcu_enabled+0x11/0x60
> [   96.876402]  ? call_timer_fn+0x4e0/0x4e0
> [   96.876402]  ? rcu_note_context_switch+0x3b0/0x3b0
> [   96.876402]  ? lock_downgrade+0x3c0/0x3c0
> [   96.876402]  ? rwlock_bug.part.1+0x60/0x60
> [   96.876402]  ? lockdep_hardirqs_on+0x16/0x2a0
> [   96.876402]  rcu_core_si+0xe/0x10
> [   96.876402]  __do_softirq+0x123/0x766
> [   96.876402]  ? do_raw_spin_unlock+0xa8/0x140
> [   96.876402]  irq_exit+0xd6/0xf0
> [   96.876402]  do_IRQ+0xa3/0x1e0
> [   96.876402]  common_interrupt+0xf/0xf
> [   96.876402]  </IRQ>
> [   96.876402] RIP: 0010:_raw_spin_unlock_irqrestore+0x46/0x50
> [   96.876402] Code: 6a 6f ff 4c 89 e7 e8 69 fb 6f ff f6 c7 02 75 13 53 9d e8 ad 4c 7f ff 65 ff 0d fe ef f8 4f 5b 41 5c 5d c3 e8 ec 4d 7f ff 53 9d <eb> eb 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 65 ff 05 db ef f8
> [   96.876402] RSP: 0000:ffffffffb0c07ab0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffcf
> [   96.876402] RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffffffffaf789c26
> [   96.876402] RDX: 0000000000000007 RSI: dffffc0000000000 RDI: ffffffffb1329794
> [   96.876402] RBP: ffffffffb0c07ac0 R08: fffffbfff626282a R09: fffffbfff626282a
> [   96.876402] R10: fffffbfff6262829 R11: ffffffffb131414b R12: ffffffffb0f8a860
> [   96.876402] R13: ffffffffb0f8a980 R14: ffffffffb982af38 R15: ffff888216688310
> [   96.876402]  ? lockdep_hardirqs_on+0x16/0x2a0
> [   96.876402]  create_object+0x4a2/0x540
> [   96.876402]  kmemleak_alloc_percpu+0xbd/0x150
> [   96.876402]  pcpu_alloc+0x50c/0xa40
> [   96.876402]  __alloc_percpu+0x15/0x20
> [   96.876402]  __percpu_init_rwsem+0x28/0xa0
> [   96.876402]  alloc_super+0x1ac/0x530
> [   96.876402]  sget_fc+0xb9/0x3a0
> [   96.876402]  ? compare_single+0x10/0x10
> [   96.876402]  ? ramfs_symlink+0xe0/0xe0
> [   96.876402]  vfs_get_super+0x4e/0x1a0
> [   96.876402]  ? vfs_parse_fs_string+0x110/0x110
> [   96.876402]  get_tree_nodev+0x16/0x20
> [   96.876402]  ramfs_get_tree+0x15/0x20
> [   96.876402]  vfs_get_tree+0x54/0x150
> [   96.876402]  fc_mount+0x14/0x60
> [   96.876402]  vfs_kern_mount.part.13+0x61/0xa0
> [   96.876402]  mnt_init+0x1b0/0x34a
> [   96.876402]  ? set_mphash_entries+0xa2/0xa2
> [   96.876402]  ? __percpu_counter_init+0x127/0x140
> [   96.876402]  vfs_caches_init+0xda/0xe6
> [   96.876402]  start_kernel+0x55d/0x5dc
> [   96.876402]  ? thread_stack_cache_init+0xb/0xb
> [   96.876402]  ? idt_setup_from_table+0xd9/0x130
> [   96.876402]  x86_64_start_reservations+0x24/0x26
> [   96.876402]  x86_64_start_kernel+0xf4/0xfb
> [   96.876402]  secondary_startup_64+0xb6/0xc0
> [   96.876402] irq event stamp: 16832
> [   96.876402] hardirqs last  enabled at (16831): [<ffffffffaf6a8399>] switch_mm+0x49/0x60
> [   96.876402] hardirqs last disabled at (16832): [<ffffffffb13c0b52>] efi_set_virtual_address_map+0x4a7/0x574
> [   96.876402] softirqs last  enabled at (15278): [<ffffffffb0400447>] __do_softirq+0x447/0x766
> [   96.876402] softirqs last disabled at (15271): [<ffffffffaf6d3ac6>] irq_exit+0xd6/0xf0
> [   96.876402] ---[ end trace 8c99b667a2f37d07 ]---
> [   96.876412] rcu: rcu_sched: wait state: RCU_GP_IDLE(0) ->state: 0x1ffff delta ->gp_activity 4294945938 ->gp_req_activity 8641 ->gp_wake_time 4294945938 ->gp_wake_seq 0 ->gp_seq -1200 ->gp_seq_needed -1196 ->gp_flags 0x1
> [   96.886409] rcu:     rcu_node 0:127 ->gp_seq -1200 ->gp_seq_needed -1196
> [   96.896408] rcu:     rcu_node 0:15 ->gp_seq -1200 ->gp_seq_needed -1196
> [   96.906408] rcu:     cpu 1 ->gp_seq_needed 0
> [   96.911146] rcu:     cpu 2 ->gp_seq_needed 0
> [   96.916407] rcu:     cpu 3 ->gp_seq_needed 0
> [   96.921145] rcu:     cpu 4 ->gp_seq_needed 0
> [   96.926407] rcu:     cpu 5 ->gp_seq_needed 0
> [   96.931145] rcu:     cpu 6 ->gp_seq_needed 0
> [   96.936407] rcu:     cpu 7 ->gp_seq_needed 0
> [   96.941145] rcu:     cpu 8 ->gp_seq_needed 0
> [   96.946407] rcu:     cpu 9 ->gp_seq_needed 0
> [   96.951145] rcu:     cpu 10 ->gp_seq_needed 0
> [   96.956407] rcu:     cpu 11 ->gp_seq_needed 0
> [   96.961231] rcu:     cpu 12 ->gp_seq_needed 0
> [   96.966407] rcu:     cpu 13 ->gp_seq_needed 0
> [   96.971231] rcu:     cpu 14 ->gp_seq_needed 0
> [   96.976055] rcu:     cpu 15 ->gp_seq_needed 0
> [   97.064605] LVT offset 2 assigned for vector 0xf4
> [   97.066435] numa_add_cpu cpu 0 node 0: mask now 0
> [   97.066440] Last level iTLB entries: 4KB 1024, 2MB 1024, 4MB 512

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21  5:09 ` Paul E. McKenney
@ 2020-01-21 11:45   ` Qian Cai
  2020-01-21 14:19     ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-21 11:45 UTC (permalink / raw)
  To: paulmck; +Cc: rcu, LKML



> On Jan 21, 2020, at 12:09 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> 
> This is what you get when a grace period has been requested, but does
> not start within 21 seconds or so.  The "->state: 0x1ffff" is a new one
> on me -- that normally happens only before RCU's grace-period kthread
> has been spawned.  But by 97 seconds after boot, it should definitely
> already be up and running.
> 
> Is the system responsive at this point?

Yes, it works fine.

> 
> Except...  Why is it taking 96 seconds for the system to get to the point
> where it prints "Dentry cache hash table entries:"?  That happens at 0.139
> seconds on my laptop.  And at about the same time on a much larger system.
> 
> I could easily imagine that all sorts of things would break when boot
> takes that long.

I suppose the kernel has CONFIG_EFI_PGT_DUMP=y, so it takes a while to run just before rcu_check_gp_start_stall().

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 11:45   ` Qian Cai
@ 2020-01-21 14:19     ` Paul E. McKenney
  2020-01-21 14:37       ` Qian Cai
  0 siblings, 1 reply; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-21 14:19 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Tue, Jan 21, 2020 at 06:45:32AM -0500, Qian Cai wrote:
> 
> 
> > On Jan 21, 2020, at 12:09 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> > 
> > This is what you get when a grace period has been requested, but does
> > not start within 21 seconds or so.  The "->state: 0x1ffff" is a new one
> > on me -- that normally happens only before RCU's grace-period kthread
> > has been spawned.  But by 97 seconds after boot, it should definitely
> > already be up and running.
> > 
> > Is the system responsive at this point?
> 
> Yes, it works fine.
> 
> > Except...  Why is it taking 96 seconds for the system to get to the point
> > where it prints "Dentry cache hash table entries:"?  That happens at 0.139
> > seconds on my laptop.  And at about the same time on a much larger system.
> > 
> > I could easily imagine that all sorts of things would break when boot
> > takes that long.
> 
> I suppose the kernel has CONFIG_EFI_PGT_DUMP=y, so it takes a while to run just before rcu_check_gp_start_stall().

New one on me!

One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
which would allow more time.

Longer term, I could suppress this warning during boot when
CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
I could provide a Kconfig option that suppressed this during boot
that was selected by whatever long-running boot-time Kconfig option
needed it.  Yet another approach would be for long-running operations
like efi_dump_pagetable() to suppress stalls on entry and re-enable them
upon exit.

Thoughts?

							Thanx, Paul

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 14:19     ` Paul E. McKenney
@ 2020-01-21 14:37       ` Qian Cai
  2020-01-21 16:15         ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-21 14:37 UTC (permalink / raw)
  To: paulmck; +Cc: rcu, LKML



> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> 
> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
> which would allow more time.

It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.

> 
> Longer term, I could suppress this warning during boot when
> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
> I could provide a Kconfig option that suppressed this during boot
> that was selected by whatever long-running boot-time Kconfig option
> needed it.  Yet another approach would be for long-running operations
> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
> upon exit.
> 
> Thoughts?

None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 14:37       ` Qian Cai
@ 2020-01-21 16:15         ` Paul E. McKenney
  2020-01-21 19:09           ` Qian Cai
  0 siblings, 1 reply; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-21 16:15 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
> 
> 
> > On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> > 
> > One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
> > which would allow more time.
> 
> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.

Indeed.  300 seconds as shown above is currently the maximum, but
please let me know if it needs to be increased.  This module parameter
is writable after boot via sysfs, so maybe that could be part of the
workaround.

> > Longer term, I could suppress this warning during boot when
> > CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
> > I could provide a Kconfig option that suppressed this during boot
> > that was selected by whatever long-running boot-time Kconfig option
> > needed it.  Yet another approach would be for long-running operations
> > like efi_dump_pagetable() to suppress stalls on entry and re-enable them
> > upon exit.
> > 
> > Thoughts?
> 
> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.

I was afraid of that.  ;-)

Could you please send me the full dmesg up to that point?  No promises,
but it might well be that I can make some broad-spectrum adjustment
within RCU.  Only one way to find out...

							Thanx, Paul

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 16:15         ` Paul E. McKenney
@ 2020-01-21 19:09           ` Qian Cai
  2020-01-21 20:46             ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-21 19:09 UTC (permalink / raw)
  To: Paul E. McKenney; +Cc: rcu, LKML



> On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> 
> On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
>> 
>> 
>>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>> 
>>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
>>> which would allow more time.
>> 
>> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
> 
> Indeed.  300 seconds as shown above is currently the maximum, but
> please let me know if it needs to be increased.  This module parameter
> is writable after boot via sysfs, so maybe that could be part of the
> workaround.
> 
>>> Longer term, I could suppress this warning during boot when
>>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
>>> I could provide a Kconfig option that suppressed this during boot
>>> that was selected by whatever long-running boot-time Kconfig option
>>> needed it.  Yet another approach would be for long-running operations
>>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
>>> upon exit.
>>> 
>>> Thoughts?
>> 
>> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
> 
> I was afraid of that.  ;-)
> 
> Could you please send me the full dmesg up to that point?  No promises,
> but it might well be that I can make some broad-spectrum adjustment
> within RCU.  Only one way to find out…

https://cailca.github.io/files/dmesg.txt


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 19:09           ` Qian Cai
@ 2020-01-21 20:46             ` Paul E. McKenney
  2020-01-22  4:16               ` Qian Cai
  0 siblings, 1 reply; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-21 20:46 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Tue, Jan 21, 2020 at 02:09:05PM -0500, Qian Cai wrote:
> > On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> > On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
> >>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>> 
> >>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
> >>> which would allow more time.
> >> 
> >> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
> > 
> > Indeed.  300 seconds as shown above is currently the maximum, but
> > please let me know if it needs to be increased.  This module parameter
> > is writable after boot via sysfs, so maybe that could be part of the
> > workaround.
> > 
> >>> Longer term, I could suppress this warning during boot when
> >>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
> >>> I could provide a Kconfig option that suppressed this during boot
> >>> that was selected by whatever long-running boot-time Kconfig option
> >>> needed it.  Yet another approach would be for long-running operations
> >>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
> >>> upon exit.
> >>> 
> >>> Thoughts?
> >> 
> >> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
> > 
> > I was afraid of that.  ;-)
> > 
> > Could you please send me the full dmesg up to that point?  No promises,
> > but it might well be that I can make some broad-spectrum adjustment
> > within RCU.  Only one way to find out…
> 
> https://cailca.github.io/files/dmesg.txt

Interesting.

Does the following (very lightly tested) patch help?

							Thanx, Paul

------------------------------------------------------------------------

commit fb21277f8f1c5cc40a8d41da2db4b0c499459821
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Tue Jan 21 12:30:22 2020 -0800

    rcu: Don't flag non-starting GPs before GP kthread is running
    
    Currently rcu_check_gp_start_stall() complains if a grace period takes
    too long to start, where "too long" is roughly one RCU CPU stall-warning
    interval.  This has worked well, but there are some debugging Kconfig
    options (such as CONFIG_EFI_PGT_DUMP=y) that can make booting take a
    very long time, so much so that the stall-warning interval has expired
    before RCU's grace-period kthread has even been spawned.
    
    This commit therefore resets the rcu_state.gp_req_activity and
    rcu_state.gp_activity timestamps just before the grace-period kthread
    is spawned, and modifies the checks and adds ordering to ensure that
    if rcu_check_gp_start_stall() sees that the grace-period kthread
    has been spawned, that it will also see the resets applied to the
    rcu_state.gp_req_activity and rcu_state.gp_activity timestamps.
    
    Reported-by: Qian Cai <cai@lca.pw>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 04718bc..d9d619d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1209,7 +1209,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
 	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
 	WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
 	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
-	if (!rcu_state.gp_kthread) {
+	if (!READ_ONCE(rcu_state.gp_kthread)) {
 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
 		goto unlock_out;
 	}
@@ -1259,10 +1259,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
  */
 static void rcu_gp_kthread_wake(void)
 {
-	if ((current == rcu_state.gp_kthread &&
+	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
 	     !in_irq() && !in_serving_softirq()) ||
 	    !READ_ONCE(rcu_state.gp_flags) ||
-	    !rcu_state.gp_kthread)
+	    !READ_ONCE(rcu_state.gp_kthread))
 		return;
 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
@@ -3619,7 +3619,10 @@ static int __init rcu_spawn_gp_kthread(void)
 	}
 	rnp = rcu_get_root();
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
-	rcu_state.gp_kthread = t;
+	WRITE_ONCE(rcu_state.gp_activity, jiffies);
+	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
+	// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
+	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	wake_up_process(t);
 	rcu_spawn_nocb_kthreads();
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 476458c..75f6e9f 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -578,6 +578,7 @@ void show_rcu_gp_kthreads(void)
 	unsigned long jw;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
+	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
 
 	j = jiffies;
 	ja = j - READ_ONCE(rcu_state.gp_activity);
@@ -585,8 +586,7 @@ void show_rcu_gp_kthreads(void)
 	jw = j - READ_ONCE(rcu_state.gp_wake_time);
 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
-		rcu_state.gp_state,
-		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
+		rcu_state.gp_state, t ? t->state : 0x1ffffL,
 		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
 		(long)READ_ONCE(rcu_state.gp_seq),
 		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
@@ -633,7 +633,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 
 	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
 	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
-	    		 READ_ONCE(rnp_root->gp_seq_needed)))
+	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
+	    !smp_load_acquire(&rcu_state.gp_kthread))
 		return;
 	j = jiffies; /* Expensive access, and in common case don't get here. */
 	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-21 20:46             ` Paul E. McKenney
@ 2020-01-22  4:16               ` Qian Cai
  2020-01-22  5:07                 ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-22  4:16 UTC (permalink / raw)
  To: Paul E. McKenney; +Cc: rcu, LKML



> On Jan 21, 2020, at 3:46 PM, Paul E. McKenney <paulmck@kernel.org> wrote:
> 
> On Tue, Jan 21, 2020 at 02:09:05PM -0500, Qian Cai wrote:
>>> On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>> On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
>>>>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>>>> 
>>>>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
>>>>> which would allow more time.
>>>> 
>>>> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
>>> 
>>> Indeed.  300 seconds as shown above is currently the maximum, but
>>> please let me know if it needs to be increased.  This module parameter
>>> is writable after boot via sysfs, so maybe that could be part of the
>>> workaround.
>>> 
>>>>> Longer term, I could suppress this warning during boot when
>>>>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
>>>>> I could provide a Kconfig option that suppressed this during boot
>>>>> that was selected by whatever long-running boot-time Kconfig option
>>>>> needed it.  Yet another approach would be for long-running operations
>>>>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
>>>>> upon exit.
>>>>> 
>>>>> Thoughts?
>>>> 
>>>> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
>>> 
>>> I was afraid of that.  ;-)
>>> 
>>> Could you please send me the full dmesg up to that point?  No promises,
>>> but it might well be that I can make some broad-spectrum adjustment
>>> within RCU.  Only one way to find out…
>> 
>> https://cailca.github.io/files/dmesg.txt
> 
> Interesting.
> 
> Does the following (very lightly tested) patch help?

Yes, it works fine.

> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit fb21277f8f1c5cc40a8d41da2db4b0c499459821
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Tue Jan 21 12:30:22 2020 -0800
> 
>    rcu: Don't flag non-starting GPs before GP kthread is running
> 
>    Currently rcu_check_gp_start_stall() complains if a grace period takes
>    too long to start, where "too long" is roughly one RCU CPU stall-warning
>    interval.  This has worked well, but there are some debugging Kconfig
>    options (such as CONFIG_EFI_PGT_DUMP=y) that can make booting take a
>    very long time, so much so that the stall-warning interval has expired
>    before RCU's grace-period kthread has even been spawned.
> 
>    This commit therefore resets the rcu_state.gp_req_activity and
>    rcu_state.gp_activity timestamps just before the grace-period kthread
>    is spawned, and modifies the checks and adds ordering to ensure that
>    if rcu_check_gp_start_stall() sees that the grace-period kthread
>    has been spawned, that it will also see the resets applied to the
>    rcu_state.gp_req_activity and rcu_state.gp_activity timestamps.
> 
>    Reported-by: Qian Cai <cai@lca.pw>
>    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 04718bc..d9d619d 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1209,7 +1209,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
> 	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
> 	WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
> 	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> -	if (!rcu_state.gp_kthread) {
> +	if (!READ_ONCE(rcu_state.gp_kthread)) {
> 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
> 		goto unlock_out;
> 	}
> @@ -1259,10 +1259,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
>  */
> static void rcu_gp_kthread_wake(void)
> {
> -	if ((current == rcu_state.gp_kthread &&
> +	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
> 	     !in_irq() && !in_serving_softirq()) ||
> 	    !READ_ONCE(rcu_state.gp_flags) ||
> -	    !rcu_state.gp_kthread)
> +	    !READ_ONCE(rcu_state.gp_kthread))
> 		return;
> 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
> 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
> @@ -3619,7 +3619,10 @@ static int __init rcu_spawn_gp_kthread(void)
> 	}
> 	rnp = rcu_get_root();
> 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
> -	rcu_state.gp_kthread = t;
> +	WRITE_ONCE(rcu_state.gp_activity, jiffies);
> +	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> +	// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
> +	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
> 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> 	wake_up_process(t);
> 	rcu_spawn_nocb_kthreads();
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 476458c..75f6e9f 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -578,6 +578,7 @@ void show_rcu_gp_kthreads(void)
> 	unsigned long jw;
> 	struct rcu_data *rdp;
> 	struct rcu_node *rnp;
> +	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
> 
> 	j = jiffies;
> 	ja = j - READ_ONCE(rcu_state.gp_activity);
> @@ -585,8 +586,7 @@ void show_rcu_gp_kthreads(void)
> 	jw = j - READ_ONCE(rcu_state.gp_wake_time);
> 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
> 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
> -		rcu_state.gp_state,
> -		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
> +		rcu_state.gp_state, t ? t->state : 0x1ffffL,
> 		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
> 		(long)READ_ONCE(rcu_state.gp_seq),
> 		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
> @@ -633,7 +633,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
> 
> 	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
> 	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
> -	    		 READ_ONCE(rnp_root->gp_seq_needed)))
> +	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
> +	    !smp_load_acquire(&rcu_state.gp_kthread))
> 		return;
> 	j = jiffies; /* Expensive access, and in common case don't get here. */
> 	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-22  4:16               ` Qian Cai
@ 2020-01-22  5:07                 ` Paul E. McKenney
  2020-01-22  5:20                   ` Qian Cai
  0 siblings, 1 reply; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-22  5:07 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Tue, Jan 21, 2020 at 11:16:06PM -0500, Qian Cai wrote:
> 
> 
> > On Jan 21, 2020, at 3:46 PM, Paul E. McKenney <paulmck@kernel.org> wrote:
> > 
> > On Tue, Jan 21, 2020 at 02:09:05PM -0500, Qian Cai wrote:
> >>> On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>> On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
> >>>>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>>>> 
> >>>>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
> >>>>> which would allow more time.
> >>>> 
> >>>> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
> >>> 
> >>> Indeed.  300 seconds as shown above is currently the maximum, but
> >>> please let me know if it needs to be increased.  This module parameter
> >>> is writable after boot via sysfs, so maybe that could be part of the
> >>> workaround.
> >>> 
> >>>>> Longer term, I could suppress this warning during boot when
> >>>>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
> >>>>> I could provide a Kconfig option that suppressed this during boot
> >>>>> that was selected by whatever long-running boot-time Kconfig option
> >>>>> needed it.  Yet another approach would be for long-running operations
> >>>>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
> >>>>> upon exit.
> >>>>> 
> >>>>> Thoughts?
> >>>> 
> >>>> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
> >>> 
> >>> I was afraid of that.  ;-)
> >>> 
> >>> Could you please send me the full dmesg up to that point?  No promises,
> >>> but it might well be that I can make some broad-spectrum adjustment
> >>> within RCU.  Only one way to find out…
> >> 
> >> https://cailca.github.io/files/dmesg.txt
> > 
> > Interesting.
> > 
> > Does the following (very lightly tested) patch help?
> 
> Yes, it works fine.

Very good, thank you!  May I apply your Tested-by?

							Thanx, Paul

> > ------------------------------------------------------------------------
> > 
> > commit fb21277f8f1c5cc40a8d41da2db4b0c499459821
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Tue Jan 21 12:30:22 2020 -0800
> > 
> >    rcu: Don't flag non-starting GPs before GP kthread is running
> > 
> >    Currently rcu_check_gp_start_stall() complains if a grace period takes
> >    too long to start, where "too long" is roughly one RCU CPU stall-warning
> >    interval.  This has worked well, but there are some debugging Kconfig
> >    options (such as CONFIG_EFI_PGT_DUMP=y) that can make booting take a
> >    very long time, so much so that the stall-warning interval has expired
> >    before RCU's grace-period kthread has even been spawned.
> > 
> >    This commit therefore resets the rcu_state.gp_req_activity and
> >    rcu_state.gp_activity timestamps just before the grace-period kthread
> >    is spawned, and modifies the checks and adds ordering to ensure that
> >    if rcu_check_gp_start_stall() sees that the grace-period kthread
> >    has been spawned, that it will also see the resets applied to the
> >    rcu_state.gp_req_activity and rcu_state.gp_activity timestamps.
> > 
> >    Reported-by: Qian Cai <cai@lca.pw>
> >    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 04718bc..d9d619d 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1209,7 +1209,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
> > 	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
> > 	WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
> > 	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> > -	if (!rcu_state.gp_kthread) {
> > +	if (!READ_ONCE(rcu_state.gp_kthread)) {
> > 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
> > 		goto unlock_out;
> > 	}
> > @@ -1259,10 +1259,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
> >  */
> > static void rcu_gp_kthread_wake(void)
> > {
> > -	if ((current == rcu_state.gp_kthread &&
> > +	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
> > 	     !in_irq() && !in_serving_softirq()) ||
> > 	    !READ_ONCE(rcu_state.gp_flags) ||
> > -	    !rcu_state.gp_kthread)
> > +	    !READ_ONCE(rcu_state.gp_kthread))
> > 		return;
> > 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
> > 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
> > @@ -3619,7 +3619,10 @@ static int __init rcu_spawn_gp_kthread(void)
> > 	}
> > 	rnp = rcu_get_root();
> > 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
> > -	rcu_state.gp_kthread = t;
> > +	WRITE_ONCE(rcu_state.gp_activity, jiffies);
> > +	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> > +	// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
> > +	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
> > 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> > 	wake_up_process(t);
> > 	rcu_spawn_nocb_kthreads();
> > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> > index 476458c..75f6e9f 100644
> > --- a/kernel/rcu/tree_stall.h
> > +++ b/kernel/rcu/tree_stall.h
> > @@ -578,6 +578,7 @@ void show_rcu_gp_kthreads(void)
> > 	unsigned long jw;
> > 	struct rcu_data *rdp;
> > 	struct rcu_node *rnp;
> > +	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
> > 
> > 	j = jiffies;
> > 	ja = j - READ_ONCE(rcu_state.gp_activity);
> > @@ -585,8 +586,7 @@ void show_rcu_gp_kthreads(void)
> > 	jw = j - READ_ONCE(rcu_state.gp_wake_time);
> > 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
> > 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
> > -		rcu_state.gp_state,
> > -		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
> > +		rcu_state.gp_state, t ? t->state : 0x1ffffL,
> > 		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
> > 		(long)READ_ONCE(rcu_state.gp_seq),
> > 		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
> > @@ -633,7 +633,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
> > 
> > 	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
> > 	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
> > -	    		 READ_ONCE(rnp_root->gp_seq_needed)))
> > +	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
> > +	    !smp_load_acquire(&rcu_state.gp_kthread))
> > 		return;
> > 	j = jiffies; /* Expensive access, and in common case don't get here. */
> > 	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
> 

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-22  5:07                 ` Paul E. McKenney
@ 2020-01-22  5:20                   ` Qian Cai
  2020-01-22 16:50                     ` Paul E. McKenney
  0 siblings, 1 reply; 12+ messages in thread
From: Qian Cai @ 2020-01-22  5:20 UTC (permalink / raw)
  To: paulmck; +Cc: rcu, LKML



> On Jan 22, 2020, at 12:07 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> 
> On Tue, Jan 21, 2020 at 11:16:06PM -0500, Qian Cai wrote:
>> 
>> 
>>> On Jan 21, 2020, at 3:46 PM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>> 
>>> On Tue, Jan 21, 2020 at 02:09:05PM -0500, Qian Cai wrote:
>>>>> On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>>>> On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
>>>>>>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
>>>>>>> 
>>>>>>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
>>>>>>> which would allow more time.
>>>>>> 
>>>>>> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
>>>>> 
>>>>> Indeed.  300 seconds as shown above is currently the maximum, but
>>>>> please let me know if it needs to be increased.  This module parameter
>>>>> is writable after boot via sysfs, so maybe that could be part of the
>>>>> workaround.
>>>>> 
>>>>>>> Longer term, I could suppress this warning during boot when
>>>>>>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
>>>>>>> I could provide a Kconfig option that suppressed this during boot
>>>>>>> that was selected by whatever long-running boot-time Kconfig option
>>>>>>> needed it.  Yet another approach would be for long-running operations
>>>>>>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
>>>>>>> upon exit.
>>>>>>> 
>>>>>>> Thoughts?
>>>>>> 
>>>>>> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
>>>>> 
>>>>> I was afraid of that.  ;-)
>>>>> 
>>>>> Could you please send me the full dmesg up to that point?  No promises,
>>>>> but it might well be that I can make some broad-spectrum adjustment
>>>>> within RCU.  Only one way to find out…
>>>> 
>>>> https://cailca.github.io/files/dmesg.txt
>>> 
>>> Interesting.
>>> 
>>> Does the following (very lightly tested) patch help?
>> 
>> Yes, it works fine.
> 
> Very good, thank you!  May I apply your Tested-by?

Just one thing minor,

Applying: Boot warning at rcu_check_gp_start_stall()
.git/rebase-apply/patch:66: space before tab in indent.
	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
warning: 1 line adds whitespace errors.

Otherwise,

Tested-by: Qian Cai <cai@lca.pw>

> 
> 							Thanx, Paul
> 
>>> ------------------------------------------------------------------------
>>> 
>>> commit fb21277f8f1c5cc40a8d41da2db4b0c499459821
>>> Author: Paul E. McKenney <paulmck@kernel.org>
>>> Date:   Tue Jan 21 12:30:22 2020 -0800
>>> 
>>>   rcu: Don't flag non-starting GPs before GP kthread is running
>>> 
>>>   Currently rcu_check_gp_start_stall() complains if a grace period takes
>>>   too long to start, where "too long" is roughly one RCU CPU stall-warning
>>>   interval.  This has worked well, but there are some debugging Kconfig
>>>   options (such as CONFIG_EFI_PGT_DUMP=y) that can make booting take a
>>>   very long time, so much so that the stall-warning interval has expired
>>>   before RCU's grace-period kthread has even been spawned.
>>> 
>>>   This commit therefore resets the rcu_state.gp_req_activity and
>>>   rcu_state.gp_activity timestamps just before the grace-period kthread
>>>   is spawned, and modifies the checks and adds ordering to ensure that
>>>   if rcu_check_gp_start_stall() sees that the grace-period kthread
>>>   has been spawned, that it will also see the resets applied to the
>>>   rcu_state.gp_req_activity and rcu_state.gp_activity timestamps.
>>> 
>>>   Reported-by: Qian Cai <cai@lca.pw>
>>>   Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>>> 
>>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>>> index 04718bc..d9d619d 100644
>>> --- a/kernel/rcu/tree.c
>>> +++ b/kernel/rcu/tree.c
>>> @@ -1209,7 +1209,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
>>> 	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
>>> 	WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
>>> 	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
>>> -	if (!rcu_state.gp_kthread) {
>>> +	if (!READ_ONCE(rcu_state.gp_kthread)) {
>>> 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
>>> 		goto unlock_out;
>>> 	}
>>> @@ -1259,10 +1259,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
>>> */
>>> static void rcu_gp_kthread_wake(void)
>>> {
>>> -	if ((current == rcu_state.gp_kthread &&
>>> +	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
>>> 	     !in_irq() && !in_serving_softirq()) ||
>>> 	    !READ_ONCE(rcu_state.gp_flags) ||
>>> -	    !rcu_state.gp_kthread)
>>> +	    !READ_ONCE(rcu_state.gp_kthread))
>>> 		return;
>>> 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
>>> 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
>>> @@ -3619,7 +3619,10 @@ static int __init rcu_spawn_gp_kthread(void)
>>> 	}
>>> 	rnp = rcu_get_root();
>>> 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
>>> -	rcu_state.gp_kthread = t;
>>> +	WRITE_ONCE(rcu_state.gp_activity, jiffies);
>>> +	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
>>> +	// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
>>> +	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
>>> 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>>> 	wake_up_process(t);
>>> 	rcu_spawn_nocb_kthreads();
>>> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
>>> index 476458c..75f6e9f 100644
>>> --- a/kernel/rcu/tree_stall.h
>>> +++ b/kernel/rcu/tree_stall.h
>>> @@ -578,6 +578,7 @@ void show_rcu_gp_kthreads(void)
>>> 	unsigned long jw;
>>> 	struct rcu_data *rdp;
>>> 	struct rcu_node *rnp;
>>> +	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
>>> 
>>> 	j = jiffies;
>>> 	ja = j - READ_ONCE(rcu_state.gp_activity);
>>> @@ -585,8 +586,7 @@ void show_rcu_gp_kthreads(void)
>>> 	jw = j - READ_ONCE(rcu_state.gp_wake_time);
>>> 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
>>> 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
>>> -		rcu_state.gp_state,
>>> -		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
>>> +		rcu_state.gp_state, t ? t->state : 0x1ffffL,
>>> 		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
>>> 		(long)READ_ONCE(rcu_state.gp_seq),
>>> 		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
>>> @@ -633,7 +633,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
>>> 
>>> 	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
>>> 	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
>>> -	    		 READ_ONCE(rnp_root->gp_seq_needed)))
>>> +	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
>>> +	    !smp_load_acquire(&rcu_state.gp_kthread))
>>> 		return;
>>> 	j = jiffies; /* Expensive access, and in common case don't get here. */
>>> 	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: Boot warning at rcu_check_gp_start_stall()
  2020-01-22  5:20                   ` Qian Cai
@ 2020-01-22 16:50                     ` Paul E. McKenney
  0 siblings, 0 replies; 12+ messages in thread
From: Paul E. McKenney @ 2020-01-22 16:50 UTC (permalink / raw)
  To: Qian Cai; +Cc: rcu, LKML

On Wed, Jan 22, 2020 at 12:20:02AM -0500, Qian Cai wrote:
> 
> 
> > On Jan 22, 2020, at 12:07 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> > 
> > On Tue, Jan 21, 2020 at 11:16:06PM -0500, Qian Cai wrote:
> >> 
> >> 
> >>> On Jan 21, 2020, at 3:46 PM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>> 
> >>> On Tue, Jan 21, 2020 at 02:09:05PM -0500, Qian Cai wrote:
> >>>>> On Jan 21, 2020, at 11:15 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>>>> On Tue, Jan 21, 2020 at 09:37:13AM -0500, Qian Cai wrote:
> >>>>>>> On Jan 21, 2020, at 9:19 AM, Paul E. McKenney <paulmck@kernel.org> wrote:
> >>>>>>> 
> >>>>>>> One approach would be to boot with rcupdate.rcu_cpu_stall_timeout=300,
> >>>>>>> which would allow more time.
> >>>>>> 
> >>>>>> It works for me if once that warning triggered,  give a bit information about adjusting the parameter when debugging options are on to suppress the warning due to expected long boot.
> >>>>> 
> >>>>> Indeed.  300 seconds as shown above is currently the maximum, but
> >>>>> please let me know if it needs to be increased.  This module parameter
> >>>>> is writable after boot via sysfs, so maybe that could be part of the
> >>>>> workaround.
> >>>>> 
> >>>>>>> Longer term, I could suppress this warning during boot when
> >>>>>>> CONFIG_EFI_PGT_DUMP=y, but that sounds quite specific.  Alternatively,
> >>>>>>> I could provide a Kconfig option that suppressed this during boot
> >>>>>>> that was selected by whatever long-running boot-time Kconfig option
> >>>>>>> needed it.  Yet another approach would be for long-running operations
> >>>>>>> like efi_dump_pagetable() to suppress stalls on entry and re-enable them
> >>>>>>> upon exit.
> >>>>>>> 
> >>>>>>> Thoughts?
> >>>>>> 
> >>>>>> None of the options sounds particularly better for me because there could come up with other options may trigger this, memtest comes in mind, for example. Then, it is a bit of pain to maintain of unknown.
> >>>>> 
> >>>>> I was afraid of that.  ;-)
> >>>>> 
> >>>>> Could you please send me the full dmesg up to that point?  No promises,
> >>>>> but it might well be that I can make some broad-spectrum adjustment
> >>>>> within RCU.  Only one way to find out…
> >>>> 
> >>>> https://cailca.github.io/files/dmesg.txt
> >>> 
> >>> Interesting.
> >>> 
> >>> Does the following (very lightly tested) patch help?
> >> 
> >> Yes, it works fine.
> > 
> > Very good, thank you!  May I apply your Tested-by?
> 
> Just one thing minor,
> 
> Applying: Boot warning at rcu_check_gp_start_stall()
> .git/rebase-apply/patch:66: space before tab in indent.
> 	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
> warning: 1 line adds whitespace errors.

Good catch, fixed!

> Otherwise,
> 
> Tested-by: Qian Cai <cai@lca.pw>

Applied, thank you!

							Thanx, Paul

> >>> ------------------------------------------------------------------------
> >>> 
> >>> commit fb21277f8f1c5cc40a8d41da2db4b0c499459821
> >>> Author: Paul E. McKenney <paulmck@kernel.org>
> >>> Date:   Tue Jan 21 12:30:22 2020 -0800
> >>> 
> >>>   rcu: Don't flag non-starting GPs before GP kthread is running
> >>> 
> >>>   Currently rcu_check_gp_start_stall() complains if a grace period takes
> >>>   too long to start, where "too long" is roughly one RCU CPU stall-warning
> >>>   interval.  This has worked well, but there are some debugging Kconfig
> >>>   options (such as CONFIG_EFI_PGT_DUMP=y) that can make booting take a
> >>>   very long time, so much so that the stall-warning interval has expired
> >>>   before RCU's grace-period kthread has even been spawned.
> >>> 
> >>>   This commit therefore resets the rcu_state.gp_req_activity and
> >>>   rcu_state.gp_activity timestamps just before the grace-period kthread
> >>>   is spawned, and modifies the checks and adds ordering to ensure that
> >>>   if rcu_check_gp_start_stall() sees that the grace-period kthread
> >>>   has been spawned, that it will also see the resets applied to the
> >>>   rcu_state.gp_req_activity and rcu_state.gp_activity timestamps.
> >>> 
> >>>   Reported-by: Qian Cai <cai@lca.pw>
> >>>   Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> >>> 
> >>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> >>> index 04718bc..d9d619d 100644
> >>> --- a/kernel/rcu/tree.c
> >>> +++ b/kernel/rcu/tree.c
> >>> @@ -1209,7 +1209,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
> >>> 	trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
> >>> 	WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
> >>> 	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> >>> -	if (!rcu_state.gp_kthread) {
> >>> +	if (!READ_ONCE(rcu_state.gp_kthread)) {
> >>> 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
> >>> 		goto unlock_out;
> >>> 	}
> >>> @@ -1259,10 +1259,10 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
> >>> */
> >>> static void rcu_gp_kthread_wake(void)
> >>> {
> >>> -	if ((current == rcu_state.gp_kthread &&
> >>> +	if ((current == READ_ONCE(rcu_state.gp_kthread) &&
> >>> 	     !in_irq() && !in_serving_softirq()) ||
> >>> 	    !READ_ONCE(rcu_state.gp_flags) ||
> >>> -	    !rcu_state.gp_kthread)
> >>> +	    !READ_ONCE(rcu_state.gp_kthread))
> >>> 		return;
> >>> 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
> >>> 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
> >>> @@ -3619,7 +3619,10 @@ static int __init rcu_spawn_gp_kthread(void)
> >>> 	}
> >>> 	rnp = rcu_get_root();
> >>> 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
> >>> -	rcu_state.gp_kthread = t;
> >>> +	WRITE_ONCE(rcu_state.gp_activity, jiffies);
> >>> +	WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
> >>> +	// Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
> >>> +	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
> >>> 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> >>> 	wake_up_process(t);
> >>> 	rcu_spawn_nocb_kthreads();
> >>> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> >>> index 476458c..75f6e9f 100644
> >>> --- a/kernel/rcu/tree_stall.h
> >>> +++ b/kernel/rcu/tree_stall.h
> >>> @@ -578,6 +578,7 @@ void show_rcu_gp_kthreads(void)
> >>> 	unsigned long jw;
> >>> 	struct rcu_data *rdp;
> >>> 	struct rcu_node *rnp;
> >>> +	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
> >>> 
> >>> 	j = jiffies;
> >>> 	ja = j - READ_ONCE(rcu_state.gp_activity);
> >>> @@ -585,8 +586,7 @@ void show_rcu_gp_kthreads(void)
> >>> 	jw = j - READ_ONCE(rcu_state.gp_wake_time);
> >>> 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
> >>> 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
> >>> -		rcu_state.gp_state,
> >>> -		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
> >>> +		rcu_state.gp_state, t ? t->state : 0x1ffffL,
> >>> 		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
> >>> 		(long)READ_ONCE(rcu_state.gp_seq),
> >>> 		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
> >>> @@ -633,7 +633,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
> >>> 
> >>> 	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
> >>> 	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
> >>> -	    		 READ_ONCE(rnp_root->gp_seq_needed)))
> >>> +	    		 READ_ONCE(rnp_root->gp_seq_needed)) ||
> >>> +	    !smp_load_acquire(&rcu_state.gp_kthread))
> >>> 		return;
> >>> 	j = jiffies; /* Expensive access, and in common case don't get here. */
> >>> 	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
> 

^ permalink raw reply	[flat|nested] 12+ messages in thread

end of thread, back to index

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-21  4:25 Boot warning at rcu_check_gp_start_stall() Qian Cai
2020-01-21  5:09 ` Paul E. McKenney
2020-01-21 11:45   ` Qian Cai
2020-01-21 14:19     ` Paul E. McKenney
2020-01-21 14:37       ` Qian Cai
2020-01-21 16:15         ` Paul E. McKenney
2020-01-21 19:09           ` Qian Cai
2020-01-21 20:46             ` Paul E. McKenney
2020-01-22  4:16               ` Qian Cai
2020-01-22  5:07                 ` Paul E. McKenney
2020-01-22  5:20                   ` Qian Cai
2020-01-22 16:50                     ` Paul E. McKenney

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