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    Subject[PATCH 4.14 034/237] char/random: silence a lockdep splat with printk()
    Date
    From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

    [ Upstream commit 1b710b1b10eff9d46666064ea25f079f70bc67a8 ]

    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

    Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
    Signed-off-by: Qian Cai <cai@lca.pw>
    Link: https://lore.kernel.org/r/1573679785-21068-1-git-send-email-cai@lca.pw
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -1687,8 +1687,9 @@ static void _warn_unseeded_randomness(co
    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);
    }

    /*

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      Last update: 2022-06-23 19:21    [W:4.748 / U:0.012 seconds]
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