char/random: silence a lockdep splat with printk()
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Message ID 1573679785-21068-1-git-send-email-cai@lca.pw
State New
Headers show
Series
  • char/random: silence a lockdep splat with printk()
Related show

Commit Message

Qian Cai Nov. 13, 2019, 9:16 p.m. UTC
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

Sergey didn't like the locking order,

uart_port->lock  ->  tty_port->lock

uart_write (uart_port->lock)
  __uart_start
    pl011_start_tx
      pl011_tx_chars
        uart_write_wakeup
          tty_port_tty_wakeup
            tty_port_default
              tty_port_tty_get (tty_port->lock)

but those code is so old, and I have no clue how to de-couple it after
checking other locks in the splat. There is an onging effort to make all
printk() as deferred, so until that happens, workaround it for now as a
short-term fix.

LTP: starting iogen01 (export LTPROOT; rwtest -N iogen01 -i 120s -s
read,write -Da -Dv -n 2 500b:$TMPDIR/doio.f1.$$
1000b:$TMPDIR/doio.f2.$$)
WARNING: possible circular locking dependency detected
------------------------------------------------------
doio/49441 is trying to acquire lock:
ffff008b7cff7290 (&(&zone->lock)->rlock){..-.}, at: rmqueue+0x138/0x2050

but task is already holding lock:
60ff000822352818 (&pool->lock/1){-.-.}, at: start_flush_work+0xd8/0x3f0

  which lock already depends on the new lock.

  the existing dependency chain (in reverse order) is:

  -> #4 (&pool->lock/1){-.-.}:
       lock_acquire+0x320/0x360
       _raw_spin_lock+0x64/0x80
       __queue_work+0x4b4/0xa10
       queue_work_on+0xac/0x11c
       tty_schedule_flip+0x84/0xbc
       tty_flip_buffer_push+0x1c/0x28
       pty_write+0x98/0xd0
       n_tty_write+0x450/0x60c
       tty_write+0x338/0x474
       __vfs_write+0x88/0x214
       vfs_write+0x12c/0x1a4
       redirected_tty_write+0x90/0xdc
       do_loop_readv_writev+0x140/0x180
       do_iter_write+0xe0/0x10c
       vfs_writev+0x134/0x1cc
       do_writev+0xbc/0x130
       __arm64_sys_writev+0x58/0x8c
       el0_svc_handler+0x170/0x240
       el0_sync_handler+0x150/0x250
       el0_sync+0x164/0x180

  -> #3 (&(&port->lock)->rlock){-.-.}:
       lock_acquire+0x320/0x360
       _raw_spin_lock_irqsave+0x7c/0x9c
       tty_port_tty_get+0x24/0x60
       tty_port_default_wakeup+0x1c/0x3c
       tty_port_tty_wakeup+0x34/0x40
       uart_write_wakeup+0x28/0x44
       pl011_tx_chars+0x1b8/0x270
       pl011_start_tx+0x24/0x70
       __uart_start+0x5c/0x68
       uart_write+0x164/0x1c8
       do_output_char+0x33c/0x348
       n_tty_write+0x4bc/0x60c
       tty_write+0x338/0x474
       redirected_tty_write+0xc0/0xdc
       do_loop_readv_writev+0x140/0x180
       do_iter_write+0xe0/0x10c
       vfs_writev+0x134/0x1cc
       do_writev+0xbc/0x130
       __arm64_sys_writev+0x58/0x8c
       el0_svc_handler+0x170/0x240
       el0_sync_handler+0x150/0x250
       el0_sync+0x164/0x180

  -> #2 (&port_lock_key){-.-.}:
       lock_acquire+0x320/0x360
       _raw_spin_lock+0x64/0x80
       pl011_console_write+0xec/0x2cc
       console_unlock+0x794/0x96c
       vprintk_emit+0x260/0x31c
       vprintk_default+0x54/0x7c
       vprintk_func+0x218/0x254
       printk+0x7c/0xa4
       register_console+0x734/0x7b0
       uart_add_one_port+0x734/0x834
       pl011_register_port+0x6c/0xac
       sbsa_uart_probe+0x234/0x2ec
       platform_drv_probe+0xd4/0x124
       really_probe+0x250/0x71c
       driver_probe_device+0xb4/0x200
       __device_attach_driver+0xd8/0x188
       bus_for_each_drv+0xbc/0x110
       __device_attach+0x120/0x220
       device_initial_probe+0x20/0x2c
       bus_probe_device+0x54/0x100
       device_add+0xae8/0xc2c
       platform_device_add+0x278/0x3b8
       platform_device_register_full+0x238/0x2ac
       acpi_create_platform_device+0x2dc/0x3a8
       acpi_bus_attach+0x390/0x3cc
       acpi_bus_attach+0x108/0x3cc
       acpi_bus_attach+0x108/0x3cc
       acpi_bus_attach+0x108/0x3cc
       acpi_bus_scan+0x7c/0xb0
       acpi_scan_init+0xe4/0x304
       acpi_init+0x100/0x114
       do_one_initcall+0x348/0x6a0
       do_initcall_level+0x190/0x1fc
       do_basic_setup+0x34/0x4c
       kernel_init_freeable+0x19c/0x260
       kernel_init+0x18/0x338
       ret_from_fork+0x10/0x18

  -> #1 (console_owner){-...}:
       lock_acquire+0x320/0x360
       console_lock_spinning_enable+0x6c/0x7c
       console_unlock+0x4f8/0x96c
       vprintk_emit+0x260/0x31c
       vprintk_default+0x54/0x7c
       vprintk_func+0x218/0x254
       printk+0x7c/0xa4
       get_random_u64+0x1c4/0x1dc
       shuffle_pick_tail+0x40/0xac
       __free_one_page+0x424/0x710
       free_one_page+0x70/0x120
       __free_pages_ok+0x61c/0xa94
       __free_pages_core+0x1bc/0x294
       memblock_free_pages+0x38/0x48
       __free_pages_memory+0xcc/0xfc
       __free_memory_core+0x70/0x78
       free_low_memory_core_early+0x148/0x18c
       memblock_free_all+0x18/0x54
       mem_init+0xb4/0x17c
       mm_init+0x14/0x38
       start_kernel+0x19c/0x530

  -> #0 (&(&zone->lock)->rlock){..-.}:
       validate_chain+0xf6c/0x2e2c
       __lock_acquire+0x868/0xc2c
       lock_acquire+0x320/0x360
       _raw_spin_lock+0x64/0x80
       rmqueue+0x138/0x2050
       get_page_from_freelist+0x474/0x688
       __alloc_pages_nodemask+0x3b4/0x18dc
       alloc_pages_current+0xd0/0xe0
       alloc_slab_page+0x2b4/0x5e0
       new_slab+0xc8/0x6bc
       ___slab_alloc+0x3b8/0x640
       kmem_cache_alloc+0x4b4/0x588
       __debug_object_init+0x778/0x8b4
       debug_object_init_on_stack+0x40/0x50
       start_flush_work+0x16c/0x3f0
       __flush_work+0xb8/0x124
       flush_work+0x20/0x30
       xlog_cil_force_lsn+0x88/0x204 [xfs]
       xfs_log_force_lsn+0x128/0x1b8 [xfs]
       xfs_file_fsync+0x3c4/0x488 [xfs]
       vfs_fsync_range+0xb0/0xd0
       generic_write_sync+0x80/0xa0 [xfs]
       xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
       xfs_file_write_iter+0x1a0/0x218 [xfs]
       __vfs_write+0x1cc/0x214
       vfs_write+0x12c/0x1a4
       ksys_write+0xb0/0x120
       __arm64_sys_write+0x54/0x88
       el0_svc_handler+0x170/0x240
       el0_sync_handler+0x150/0x250
       el0_sync+0x164/0x180

       other info that might help us debug this:

 Chain exists of:
   &(&zone->lock)->rlock --> &(&port->lock)->rlock --> &pool->lock/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pool->lock/1);
                               lock(&(&port->lock)->rlock);
                               lock(&pool->lock/1);
  lock(&(&zone->lock)->rlock);

                *** DEADLOCK ***

4 locks held by doio/49441:
 #0: a0ff00886fc27408 (sb_writers#8){.+.+}, at: vfs_write+0x118/0x1a4
 #1: 8fff00080810dfe0 (&xfs_nondir_ilock_class){++++}, at:
xfs_ilock+0x2a8/0x300 [xfs]
 #2: ffff9000129f2390 (rcu_read_lock){....}, at:
rcu_lock_acquire+0x8/0x38
 #3: 60ff000822352818 (&pool->lock/1){-.-.}, at:
start_flush_work+0xd8/0x3f0

               stack backtrace:
CPU: 48 PID: 49441 Comm: doio Tainted: G        W
Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS
L50_5.13_1.11 06/18/2019
Call trace:
 dump_backtrace+0x0/0x248
 show_stack+0x20/0x2c
 dump_stack+0xe8/0x150
 print_circular_bug+0x368/0x380
 check_noncircular+0x28c/0x294
 validate_chain+0xf6c/0x2e2c
 __lock_acquire+0x868/0xc2c
 lock_acquire+0x320/0x360
 _raw_spin_lock+0x64/0x80
 rmqueue+0x138/0x2050
 get_page_from_freelist+0x474/0x688
 __alloc_pages_nodemask+0x3b4/0x18dc
 alloc_pages_current+0xd0/0xe0
 alloc_slab_page+0x2b4/0x5e0
 new_slab+0xc8/0x6bc
 ___slab_alloc+0x3b8/0x640
 kmem_cache_alloc+0x4b4/0x588
 __debug_object_init+0x778/0x8b4
 debug_object_init_on_stack+0x40/0x50
 start_flush_work+0x16c/0x3f0
 __flush_work+0xb8/0x124
 flush_work+0x20/0x30
 xlog_cil_force_lsn+0x88/0x204 [xfs]
 xfs_log_force_lsn+0x128/0x1b8 [xfs]
 xfs_file_fsync+0x3c4/0x488 [xfs]
 vfs_fsync_range+0xb0/0xd0
 generic_write_sync+0x80/0xa0 [xfs]
 xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
 xfs_file_write_iter+0x1a0/0x218 [xfs]
 __vfs_write+0x1cc/0x214
 vfs_write+0x12c/0x1a4
 ksys_write+0xb0/0x120
 __arm64_sys_write+0x54/0x88
 el0_svc_handler+0x170/0x240
 el0_sync_handler+0x150/0x250
 el0_sync+0x164/0x180

[cai@lca.pw: add a commit log.]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Qian Cai <cai@lca.pw>
---

Sergey, please let us know if you are fine with the Signed-off-by.

 drivers/char/random.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Qian Cai Dec. 3, 2019, 6:46 p.m. UTC | #1
> On Nov 13, 2019, at 4:16 PM, Qian Cai <cai@lca.pw> wrote:
> 
> From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> 
> Sergey didn't like the locking order,
> 
> uart_port->lock  ->  tty_port->lock
> 
> uart_write (uart_port->lock)
>  __uart_start
>    pl011_start_tx
>      pl011_tx_chars
>        uart_write_wakeup
>          tty_port_tty_wakeup
>            tty_port_default
>              tty_port_tty_get (tty_port->lock)
> 
> but those code is so old, and I have no clue how to de-couple it after
> checking other locks in the splat. There is an onging effort to make all
> printk() as deferred, so until that happens, workaround it for now as a
> short-term fix.

Sergey, could we have a ACK from you so Ted might be able to merge?

> 
> LTP: starting iogen01 (export LTPROOT; rwtest -N iogen01 -i 120s -s
> read,write -Da -Dv -n 2 500b:$TMPDIR/doio.f1.$$
> 1000b:$TMPDIR/doio.f2.$$)
> WARNING: possible circular locking dependency detected
> ------------------------------------------------------
> doio/49441 is trying to acquire lock:
> ffff008b7cff7290 (&(&zone->lock)->rlock){..-.}, at: rmqueue+0x138/0x2050
> 
> but task is already holding lock:
> 60ff000822352818 (&pool->lock/1){-.-.}, at: start_flush_work+0xd8/0x3f0
> 
>  which lock already depends on the new lock.
> 
>  the existing dependency chain (in reverse order) is:
> 
>  -> #4 (&pool->lock/1){-.-.}:
>       lock_acquire+0x320/0x360
>       _raw_spin_lock+0x64/0x80
>       __queue_work+0x4b4/0xa10
>       queue_work_on+0xac/0x11c
>       tty_schedule_flip+0x84/0xbc
>       tty_flip_buffer_push+0x1c/0x28
>       pty_write+0x98/0xd0
>       n_tty_write+0x450/0x60c
>       tty_write+0x338/0x474
>       __vfs_write+0x88/0x214
>       vfs_write+0x12c/0x1a4
>       redirected_tty_write+0x90/0xdc
>       do_loop_readv_writev+0x140/0x180
>       do_iter_write+0xe0/0x10c
>       vfs_writev+0x134/0x1cc
>       do_writev+0xbc/0x130
>       __arm64_sys_writev+0x58/0x8c
>       el0_svc_handler+0x170/0x240
>       el0_sync_handler+0x150/0x250
>       el0_sync+0x164/0x180
> 
>  -> #3 (&(&port->lock)->rlock){-.-.}:
>       lock_acquire+0x320/0x360
>       _raw_spin_lock_irqsave+0x7c/0x9c
>       tty_port_tty_get+0x24/0x60
>       tty_port_default_wakeup+0x1c/0x3c
>       tty_port_tty_wakeup+0x34/0x40
>       uart_write_wakeup+0x28/0x44
>       pl011_tx_chars+0x1b8/0x270
>       pl011_start_tx+0x24/0x70
>       __uart_start+0x5c/0x68
>       uart_write+0x164/0x1c8
>       do_output_char+0x33c/0x348
>       n_tty_write+0x4bc/0x60c
>       tty_write+0x338/0x474
>       redirected_tty_write+0xc0/0xdc
>       do_loop_readv_writev+0x140/0x180
>       do_iter_write+0xe0/0x10c
>       vfs_writev+0x134/0x1cc
>       do_writev+0xbc/0x130
>       __arm64_sys_writev+0x58/0x8c
>       el0_svc_handler+0x170/0x240
>       el0_sync_handler+0x150/0x250
>       el0_sync+0x164/0x180
> 
>  -> #2 (&port_lock_key){-.-.}:
>       lock_acquire+0x320/0x360
>       _raw_spin_lock+0x64/0x80
>       pl011_console_write+0xec/0x2cc
>       console_unlock+0x794/0x96c
>       vprintk_emit+0x260/0x31c
>       vprintk_default+0x54/0x7c
>       vprintk_func+0x218/0x254
>       printk+0x7c/0xa4
>       register_console+0x734/0x7b0
>       uart_add_one_port+0x734/0x834
>       pl011_register_port+0x6c/0xac
>       sbsa_uart_probe+0x234/0x2ec
>       platform_drv_probe+0xd4/0x124
>       really_probe+0x250/0x71c
>       driver_probe_device+0xb4/0x200
>       __device_attach_driver+0xd8/0x188
>       bus_for_each_drv+0xbc/0x110
>       __device_attach+0x120/0x220
>       device_initial_probe+0x20/0x2c
>       bus_probe_device+0x54/0x100
>       device_add+0xae8/0xc2c
>       platform_device_add+0x278/0x3b8
>       platform_device_register_full+0x238/0x2ac
>       acpi_create_platform_device+0x2dc/0x3a8
>       acpi_bus_attach+0x390/0x3cc
>       acpi_bus_attach+0x108/0x3cc
>       acpi_bus_attach+0x108/0x3cc
>       acpi_bus_attach+0x108/0x3cc
>       acpi_bus_scan+0x7c/0xb0
>       acpi_scan_init+0xe4/0x304
>       acpi_init+0x100/0x114
>       do_one_initcall+0x348/0x6a0
>       do_initcall_level+0x190/0x1fc
>       do_basic_setup+0x34/0x4c
>       kernel_init_freeable+0x19c/0x260
>       kernel_init+0x18/0x338
>       ret_from_fork+0x10/0x18
> 
>  -> #1 (console_owner){-...}:
>       lock_acquire+0x320/0x360
>       console_lock_spinning_enable+0x6c/0x7c
>       console_unlock+0x4f8/0x96c
>       vprintk_emit+0x260/0x31c
>       vprintk_default+0x54/0x7c
>       vprintk_func+0x218/0x254
>       printk+0x7c/0xa4
>       get_random_u64+0x1c4/0x1dc
>       shuffle_pick_tail+0x40/0xac
>       __free_one_page+0x424/0x710
>       free_one_page+0x70/0x120
>       __free_pages_ok+0x61c/0xa94
>       __free_pages_core+0x1bc/0x294
>       memblock_free_pages+0x38/0x48
>       __free_pages_memory+0xcc/0xfc
>       __free_memory_core+0x70/0x78
>       free_low_memory_core_early+0x148/0x18c
>       memblock_free_all+0x18/0x54
>       mem_init+0xb4/0x17c
>       mm_init+0x14/0x38
>       start_kernel+0x19c/0x530
> 
>  -> #0 (&(&zone->lock)->rlock){..-.}:
>       validate_chain+0xf6c/0x2e2c
>       __lock_acquire+0x868/0xc2c
>       lock_acquire+0x320/0x360
>       _raw_spin_lock+0x64/0x80
>       rmqueue+0x138/0x2050
>       get_page_from_freelist+0x474/0x688
>       __alloc_pages_nodemask+0x3b4/0x18dc
>       alloc_pages_current+0xd0/0xe0
>       alloc_slab_page+0x2b4/0x5e0
>       new_slab+0xc8/0x6bc
>       ___slab_alloc+0x3b8/0x640
>       kmem_cache_alloc+0x4b4/0x588
>       __debug_object_init+0x778/0x8b4
>       debug_object_init_on_stack+0x40/0x50
>       start_flush_work+0x16c/0x3f0
>       __flush_work+0xb8/0x124
>       flush_work+0x20/0x30
>       xlog_cil_force_lsn+0x88/0x204 [xfs]
>       xfs_log_force_lsn+0x128/0x1b8 [xfs]
>       xfs_file_fsync+0x3c4/0x488 [xfs]
>       vfs_fsync_range+0xb0/0xd0
>       generic_write_sync+0x80/0xa0 [xfs]
>       xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
>       xfs_file_write_iter+0x1a0/0x218 [xfs]
>       __vfs_write+0x1cc/0x214
>       vfs_write+0x12c/0x1a4
>       ksys_write+0xb0/0x120
>       __arm64_sys_write+0x54/0x88
>       el0_svc_handler+0x170/0x240
>       el0_sync_handler+0x150/0x250
>       el0_sync+0x164/0x180
> 
>       other info that might help us debug this:
> 
> Chain exists of:
>   &(&zone->lock)->rlock --> &(&port->lock)->rlock --> &pool->lock/1
> 
> Possible unsafe locking scenario:
> 
>       CPU0                    CPU1
>       ----                    ----
>  lock(&pool->lock/1);
>                               lock(&(&port->lock)->rlock);
>                               lock(&pool->lock/1);
>  lock(&(&zone->lock)->rlock);
> 
>                *** DEADLOCK ***
> 
> 4 locks held by doio/49441:
> #0: a0ff00886fc27408 (sb_writers#8){.+.+}, at: vfs_write+0x118/0x1a4
> #1: 8fff00080810dfe0 (&xfs_nondir_ilock_class){++++}, at:
> xfs_ilock+0x2a8/0x300 [xfs]
> #2: ffff9000129f2390 (rcu_read_lock){....}, at:
> rcu_lock_acquire+0x8/0x38
> #3: 60ff000822352818 (&pool->lock/1){-.-.}, at:
> start_flush_work+0xd8/0x3f0
> 
>               stack backtrace:
> CPU: 48 PID: 49441 Comm: doio Tainted: G        W
> Hardware name: HPE Apollo 70             /C01_APACHE_MB         , BIOS
> L50_5.13_1.11 06/18/2019
> Call trace:
> dump_backtrace+0x0/0x248
> show_stack+0x20/0x2c
> dump_stack+0xe8/0x150
> print_circular_bug+0x368/0x380
> check_noncircular+0x28c/0x294
> validate_chain+0xf6c/0x2e2c
> __lock_acquire+0x868/0xc2c
> lock_acquire+0x320/0x360
> _raw_spin_lock+0x64/0x80
> rmqueue+0x138/0x2050
> get_page_from_freelist+0x474/0x688
> __alloc_pages_nodemask+0x3b4/0x18dc
> alloc_pages_current+0xd0/0xe0
> alloc_slab_page+0x2b4/0x5e0
> new_slab+0xc8/0x6bc
> ___slab_alloc+0x3b8/0x640
> kmem_cache_alloc+0x4b4/0x588
> __debug_object_init+0x778/0x8b4
> debug_object_init_on_stack+0x40/0x50
> start_flush_work+0x16c/0x3f0
> __flush_work+0xb8/0x124
> flush_work+0x20/0x30
> xlog_cil_force_lsn+0x88/0x204 [xfs]
> xfs_log_force_lsn+0x128/0x1b8 [xfs]
> xfs_file_fsync+0x3c4/0x488 [xfs]
> vfs_fsync_range+0xb0/0xd0
> generic_write_sync+0x80/0xa0 [xfs]
> xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
> xfs_file_write_iter+0x1a0/0x218 [xfs]
> __vfs_write+0x1cc/0x214
> vfs_write+0x12c/0x1a4
> ksys_write+0xb0/0x120
> __arm64_sys_write+0x54/0x88
> el0_svc_handler+0x170/0x240
> el0_sync_handler+0x150/0x250
> el0_sync+0x164/0x180
> 
> [cai@lca.pw: add a commit log.]
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> 
> Sergey, please let us know if you are fine with the Signed-off-by.
> 
> drivers/char/random.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 46afd14facb7..b90086c9836f 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1688,8 +1688,9 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller,
> 	print_once = true;
> #endif
> 	if (__ratelimit(&unseeded_warning))
> -		pr_notice("random: %s called from %pS with crng_init=%d\n",
> -			  func_name, caller, crng_init);
> +		printk_deferred(KERN_NOTICE "random: %s called from %pS "
> +				"with crng_init=%d\n", func_name, caller,
> +				crng_init);
> }
> 
> /*
> -- 
> 1.8.3.1
>
Sergey Senozhatsky Dec. 5, 2019, 1 a.m. UTC | #2
Hi,

On (19/12/03 13:46), Qian Cai wrote:
> > On Nov 13, 2019, at 4:16 PM, Qian Cai <cai@lca.pw> wrote:
> > 
> > From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> > 
> > Sergey didn't like the locking order,
> > 
> > uart_port->lock  ->  tty_port->lock
> > 
> > uart_write (uart_port->lock)
> >  __uart_start
> >    pl011_start_tx
> >      pl011_tx_chars
> >        uart_write_wakeup
> >          tty_port_tty_wakeup
> >            tty_port_default
> >              tty_port_tty_get (tty_port->lock)
> > 
> > but those code is so old, and I have no clue how to de-couple it after
> > checking other locks in the splat. There is an onging effort to make all
> > printk() as deferred, so until that happens, workaround it for now as a
> > short-term fix.
> 
> Sergey, could we have a ACK from you so Ted might be able to merge?

Not sure if I can ACK it, but overall it makes sense to use deferred
printk there.

[..]
> 
> > [cai@lca.pw: add a commit log.]
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> > Signed-off-by: Qian Cai <cai@lca.pw>
> > ---
> > 
> > Sergey, please let us know if you are fine with the Signed-off-by.

A 'Reviewed-by' will suffice.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss
Qian Cai Dec. 17, 2019, 1:52 a.m. UTC | #3
> On Dec 4, 2019, at 8:00 PM, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> 
> A 'Reviewed-by' will suffice.
> 
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Ted, could you take a look at this trivial patch?
Qian Cai Jan. 2, 2020, 3:42 p.m. UTC | #4
> On Dec 16, 2019, at 8:52 PM, Qian Cai <cai@lca.pw> wrote:
> 
> 
> 
>> On Dec 4, 2019, at 8:00 PM, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
>> 
>> A 'Reviewed-by' will suffice.
>> 
>> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> 
> Ted, could you take a look at this trivial patch?

Not sure if Ted is still interested in maintaining this file as he had no feedback for more
than a month. The problem is that this will render the lockdep useless for a general
debugging tool as it will disable the lockdep early in the process.

Could Andrew (since the free page shuffle will call get_random) or Linus pick this up
directly with the approval from one of the printk() maintainers above?

https://lore.kernel.org/lkml/1573679785-21068-1-git-send-email-cai@lca.pw/
Steven Rostedt Jan. 2, 2020, 5:07 p.m. UTC | #5
On Thu, 2 Jan 2020 10:42:51 -0500
Qian Cai <cai@lca.pw> wrote:

> > On Dec 16, 2019, at 8:52 PM, Qian Cai <cai@lca.pw> wrote:
> > 
> > 
> >   
> >> On Dec 4, 2019, at 8:00 PM, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> >> 
> >> A 'Reviewed-by' will suffice.
> >> 
> >> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>  
> > 
> > Ted, could you take a look at this trivial patch?  
> 
> Not sure if Ted is still interested in maintaining this file as he had no feedback for more
> than a month. The problem is that this will render the lockdep useless for a general
> debugging tool as it will disable the lockdep early in the process.
> 

How would this disable lockdep early in the process? The patch is just
changing pr_notice() to printk_deferred() correct?

-- Steve
Qian Cai Jan. 2, 2020, 5:16 p.m. UTC | #6
> On Jan 2, 2020, at 12:07 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> How would this disable lockdep early in the process? The patch is just
> changing pr_notice() to printk_deferred() correct?

Yes, I meant without this patch. Lockdep will easily generate this potential deadlock warning early after boot and then disable itself.
Theodore Y. Ts'o Jan. 2, 2020, 6 p.m. UTC | #7
On Thu, Jan 02, 2020 at 10:42:51AM -0500, Qian Cai wrote:
> 
> Not sure if Ted is still interested in maintaining this file as he had no feedback for more
> than a month. The problem is that this will render the lockdep useless for a general
> debugging tool as it will disable the lockdep early in the process.
> 
> Could Andrew (since the free page shuffle will call get_random) or Linus pick this up
> directly with the approval from one of the printk() maintainers above?

Sorry, things have been busy with the Chistmas holidays and getting
the ext4 tree ready for the merge window.  I'll take a look at this in the next day or two.

    	      	    	    	  - Ted
Theodore Y. Ts'o Jan. 7, 2020, 9:07 p.m. UTC | #8
On Wed, Nov 13, 2019 at 04:16:25PM -0500, Qian Cai wrote:
> From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> 
> Sergey didn't like the locking order,
> 
> uart_port->lock  ->  tty_port->lock
> 
> uart_write (uart_port->lock)
>   __uart_start
>     pl011_start_tx
>       pl011_tx_chars
>         uart_write_wakeup
>           tty_port_tty_wakeup
>             tty_port_default
>               tty_port_tty_get (tty_port->lock)
> 
> but those code is so old, and I have no clue how to de-couple it after
> checking other locks in the splat. There is an onging effort to make all
> printk() as deferred, so until that happens, workaround it for now as a
> short-term fix.

Applied, thanks.

					- Ted

Patch
diff mbox series

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 46afd14facb7..b90086c9836f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1688,8 +1688,9 @@  static void _warn_unseeded_randomness(const char *func_name, void *caller,
 	print_once = true;
 #endif
 	if (__ratelimit(&unseeded_warning))
-		pr_notice("random: %s called from %pS with crng_init=%d\n",
-			  func_name, caller, crng_init);
+		printk_deferred(KERN_NOTICE "random: %s called from %pS "
+				"with crng_init=%d\n", func_name, caller,
+				crng_init);
 }
 
 /*