From 2bbc39ce7809b1e2cd0f96103d4510550a96d02f Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sun, 24 Jul 2022 16:51:48 +0200 Subject: [PATCH] Revert "Revert "char/random: silence a lockdep splat with printk()"" In 2019, Sergey fixed a lockdep splat with 15341b1dd409 ("char/random: silence a lockdep splat with printk()"), but that got reverted soon after from 4.19 because back then it apparently caused various problems. But the issue it was fixing is still there, and more generally, many patches turning printk() into printk_deferred() have landed since, making me suspect it's okay to try this out again. This should fix the following deadlock found by the kernel test robot: [ 18.287691] WARNING: possible circular locking dependency detected [ 18.287692] 4.19.248-00165-g3d1f971aa81f #1 Not tainted [ 18.287693] ------------------------------------------------------ [ 18.287712] stop/202 is trying to acquire lock: [ 18.287713] (ptrval) (console_owner){..-.}, at: console_unlock (??:?) [ 18.287717] [ 18.287718] but task is already holding lock: [ 18.287718] (ptrval) (&(&port->lock)->rlock){-...}, at: pty_write (pty.c:?) [ 18.287722] [ 18.287722] which lock already depends on the new lock. [ 18.287723] [ 18.287724] [ 18.287725] the existing dependency chain (in reverse order) is: [ 18.287725] [ 18.287726] -> #2 (&(&port->lock)->rlock){-...}: [ 18.287729] validate_chain+0x84a/0xe00 [ 18.287729] __lock_acquire (lockdep.c:?) [ 18.287730] lock_acquire (??:?) [ 18.287731] _raw_spin_lock_irqsave (??:?) [ 18.287732] tty_port_tty_get (??:?) [ 18.287733] tty_port_default_wakeup (tty_port.c:?) [ 18.287734] tty_port_tty_wakeup (??:?) [ 18.287734] uart_write_wakeup (??:?) [ 18.287735] serial8250_tx_chars (??:?) [ 18.287736] serial8250_handle_irq (??:?) [ 18.287737] serial8250_default_handle_irq (8250_port.c:?) [ 18.287738] serial8250_interrupt (8250_core.c:?) [ 18.287738] __handle_irq_event_percpu (??:?) [ 18.287739] handle_irq_event_percpu (??:?) [ 18.287740] handle_irq_event (??:?) [ 18.287741] handle_edge_irq (??:?) [ 18.287742] handle_irq (??:?) [ 18.287742] do_IRQ (??:?) [ 18.287743] common_interrupt (entry_32.o:?) [ 18.287744] _raw_spin_unlock_irqrestore (??:?) [ 18.287745] uart_write (serial_core.c:?) [ 18.287746] process_output_block (n_tty.c:?) [ 18.287747] n_tty_write (n_tty.c:?) [ 18.287747] tty_write (tty_io.c:?) [ 18.287748] __vfs_write (??:?) [ 18.287749] vfs_write (??:?) [ 18.287750] ksys_write (??:?) [ 18.287750] sys_write (??:?) [ 18.287751] do_fast_syscall_32 (??:?) [ 18.287752] entry_SYSENTER_32 (??:?) [ 18.287752] [ 18.287753] -> #1 (&port_lock_key){-.-.}: [ 18.287756] [ 18.287756] -> #0 (console_owner){..-.}: [ 18.287759] check_prevs_add (lockdep.c:?) [ 18.287760] validate_chain+0x84a/0xe00 [ 18.287761] __lock_acquire (lockdep.c:?) [ 18.287761] lock_acquire (??:?) [ 18.287762] console_unlock (??:?) [ 18.287763] vprintk_emit (??:?) [ 18.287764] vprintk_default (??:?) [ 18.287764] vprintk_func (??:?) [ 18.287765] printk (??:?) [ 18.287766] get_random_u32 (??:?) [ 18.287767] shuffle_freelist (slub.c:?) [ 18.287767] allocate_slab (slub.c:?) [ 18.287768] new_slab (slub.c:?) [ 18.287769] ___slab_alloc+0x6d0/0xb20 [ 18.287770] __slab_alloc+0xd6/0x2e0 [ 18.287770] __kmalloc (??:?) [ 18.287771] tty_buffer_alloc (tty_buffer.c:?) [ 18.287772] __tty_buffer_request_room (tty_buffer.c:?) [ 18.287773] tty_insert_flip_string_fixed_flag (??:?) [ 18.287774] pty_write (pty.c:?) [ 18.287775] process_output_block (n_tty.c:?) [ 18.287776] n_tty_write (n_tty.c:?) [ 18.287777] tty_write (tty_io.c:?) [ 18.287778] __vfs_write (??:?) [ 18.287779] vfs_write (??:?) [ 18.287780] ksys_write (??:?) [ 18.287780] sys_write (??:?) [ 18.287781] do_fast_syscall_32 (??:?) [ 18.287782] entry_SYSENTER_32 (??:?) [ 18.287783] [ 18.287783] other info that might help us debug this: [ 18.287784] [ 18.287785] Chain exists of: [ 18.287785] console_owner --> &port_lock_key --> &(&port->lock)->rlock [ 18.287789] [ 18.287790] Possible unsafe locking scenario: [ 18.287790] [ 18.287791] CPU0 CPU1 [ 18.287792] ---- ---- [ 18.287792] lock(&(&port->lock)->rlock); [ 18.287794] lock(&port_lock_key); [ 18.287814] lock(&(&port->lock)->rlock); [ 18.287815] lock(console_owner); [ 18.287817] [ 18.287818] *** DEADLOCK *** [ 18.287818] [ 18.287819] 6 locks held by stop/202: [ 18.287820] #0: (ptrval) (&tty->ldisc_sem){++++}, at: ldsem_down_read (??:?) [ 18.287823] #1: (ptrval) (&tty->atomic_write_lock){+.+.}, at: tty_write_lock (tty_io.c:?) [ 18.287826] #2: (ptrval) (&o_tty->termios_rwsem/1){++++}, at: n_tty_write (n_tty.c:?) [ 18.287830] #3: (ptrval) (&ldata->output_lock){+.+.}, at: process_output_block (n_tty.c:?) [ 18.287834] #4: (ptrval) (&(&port->lock)->rlock){-...}, at: pty_write (pty.c:?) [ 18.287838] #5: (ptrval) (console_lock){+.+.}, at: console_trylock_spinning (printk.c:?) [ 18.287841] [ 18.287842] stack backtrace: [ 18.287843] CPU: 0 PID: 202 Comm: stop Not tainted 4.19.248-00165-g3d1f971aa81f #1 [ 18.287843] Call Trace: [ 18.287844] dump_stack (??:?) [ 18.287845] print_circular_bug.cold+0x78/0x8b [ 18.287846] check_prev_add+0x66a/0xd20 [ 18.287847] check_prevs_add (lockdep.c:?) [ 18.287848] validate_chain+0x84a/0xe00 [ 18.287848] __lock_acquire (lockdep.c:?) [ 18.287849] lock_acquire (??:?) [ 18.287850] ? console_unlock (??:?) [ 18.287851] console_unlock (??:?) [ 18.287851] ? console_unlock (??:?) [ 18.287852] ? native_save_fl (??:?) [ 18.287853] vprintk_emit (??:?) [ 18.287854] vprintk_default (??:?) [ 18.287855] vprintk_func (??:?) [ 18.287855] printk (??:?) [ 18.287856] get_random_u32 (??:?) [ 18.287857] ? shuffle_freelist (slub.c:?) [ 18.287858] shuffle_freelist (slub.c:?) [ 18.287858] ? page_address (??:?) [ 18.287859] allocate_slab (slub.c:?) [ 18.287860] new_slab (slub.c:?) [ 18.287861] ? pvclock_clocksource_read (??:?) [ 18.287862] ___slab_alloc+0x6d0/0xb20 [ 18.287862] ? kvm_sched_clock_read (kvmclock.c:?) [ 18.287863] ? __slab_alloc+0xbc/0x2e0 [ 18.287864] ? native_wbinvd (paravirt.c:?) [ 18.287865] __slab_alloc+0xd6/0x2e0 [ 18.287865] __kmalloc (??:?) [ 18.287866] ? __lock_acquire (lockdep.c:?) [ 18.287867] ? tty_buffer_alloc (tty_buffer.c:?) [ 18.287868] tty_buffer_alloc (tty_buffer.c:?) [ 18.287869] __tty_buffer_request_room (tty_buffer.c:?) [ 18.287869] tty_insert_flip_string_fixed_flag (??:?) [ 18.287870] pty_write (pty.c:?) [ 18.287871] process_output_block (n_tty.c:?) [ 18.287872] n_tty_write (n_tty.c:?) [ 18.287873] ? print_dl_stats (??:?) [ 18.287874] ? n_tty_ioctl (n_tty.c:?) [ 18.287874] tty_write (tty_io.c:?) [ 18.287875] ? n_tty_ioctl (n_tty.c:?) [ 18.287876] ? tty_write_unlock (tty_io.c:?) [ 18.287877] __vfs_write (??:?) [ 18.287877] vfs_write (??:?) [ 18.287878] ? __fget_light (file.c:?) [ 18.287879] ksys_write (??:?) Cc: Sergey Senozhatsky Cc: Qian Cai Cc: Lech Perczak Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Cc: Sasha Levin Cc: Petr Mladek Cc: John Ogness Reported-by: kernel test robot Link: https://lore.kernel.org/lkml/Ytz+lo4zRQYG3JUR@xsang-OptiPlex-9020 Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 38591c53ea57..1cbc33ee5a5f 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -184,8 +184,8 @@ static void __cold process_random_ready_list(void) #define warn_unseeded_randomness() \ if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \ - pr_notice("%s called from %pS with crng_init=%d\n", \ - __func__, (void *)_RET_IP_, crng_init) + printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \ + __func__, (void *)_RET_IP_, crng_init) /*********************************************************************