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SubjectRe: INFO: rcu detected stall in n_tty_receive_char_special
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Date
Dmitry Vyukov wrote:
> This looks somewhat similar to "INFO: rcu detected stall in __process_echoes":
> https://syzkaller.appspot.com/bug?id=17f23b094cd80df750e5b0f8982c521ee6bcbf40
> But I am not sure because stall stacks are somewhat different.

Yes, this will be the same one which can be reproduced using same reproducer
provided by syzbot. You can try below one like "while :; do echo -n .; ./a.out; done".

----------------------------------------
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
int fd[2];
unsigned int zero = 0;
char buf[128];
int ptyno = 0;
char c = 0;
char data[64] = { };
while (1) {
fd[0] = open("/dev/ptmx", O_RDWR);
ioctl(fd[0], TIOCSPTLCK, &zero);
write(fd[0], data, sizeof(data));
if (ioctl(fd[0], TIOCGPTN, &ptyno))
break;
sprintf(buf, "/dev/pts/%d", ptyno);
fd[1] = open(buf, O_RDONLY);
if (fd[1] == EOF)
break;
ioctl(fd[1], TIOCSTI, &c);
}
return 1;
}
----------------------------------------

Since tty subsystem is prone to race condition, same reproducer can hit
various different results.

[ 524.349009] a.out R running task 0 4052 1 0x80000084
[ 524.350879] Call Trace:
[ 524.351816] <IRQ>
[ 524.352672] sched_show_task+0x16b/0x230
[ 524.353864] show_state_filter+0x9d/0x190
[ 524.355098] sysrq_handle_showstate+0x7/0x10
[ 524.356342] __handle_sysrq+0x123/0x200
[ 524.357566] sysrq_filter+0x356/0x390
[ 524.358710] input_to_handler+0x4b/0xf0
[ 524.359911] input_pass_values.part.2+0x1ba/0x260
[ 524.361267] input_handle_event+0x11a/0x4f0
[ 524.362504] input_event+0x45/0x60
[ 524.363601] atkbd_interrupt+0x41a/0x6f0
[ 524.364815] serio_interrupt+0x3b/0x80
[ 524.365975] i8042_interrupt+0x1e8/0x3a0
[ 524.367197] ? _raw_spin_unlock_irq+0x24/0x40
[ 524.368456] __handle_irq_event_percpu+0x5b/0xc0
[ 524.369797] handle_irq_event_percpu+0x1b/0x50
[ 524.371102] handle_irq_event+0x2f/0x50
[ 524.372245] handle_edge_irq+0xcc/0x1a0
[ 524.373433] handle_irq+0x11/0x20
[ 524.374519] do_IRQ+0x52/0x100
[ 524.375519] common_interrupt+0xf/0xf
[ 524.376648] </IRQ>
[ 524.377473] RIP: 0010:n_tty_receive_char_special+0x4d1/0xad0
[ 524.379032] RSP: 0018:ffffc90006d2bd08 EFLAGS: 00000293 ORIG_RAX: ffffffffffffffd2
[ 524.380957] RAX: ffffc90010f7d000 RBX: ffffc90010f7d000 RCX: 00000011c8d443f0
[ 524.382783] RDX: 00000000000003ef RSI: ffff880126ce3800 RDI: 0000000000000000
[ 524.384644] RBP: ffff880126ce3800 R08: 0000000000000012 R09: 0000000000000000
[ 524.386479] R10: 0000000000000000 R11: ffffffff814184f3 R12: 0000000000000012
[ 524.388300] R13: ffff880126ce3800 R14: 0000000a13a9e288 R15: 0000000000000012
[ 524.390158] ? n_tty_receive_buf_common+0x43/0xd00
[ 524.391567] ? n_tty_receive_char_special+0x4ea/0xad0
[ 524.393052] ? n_tty_receive_buf_common+0x43/0xd00
[ 524.394464] n_tty_receive_buf_common+0xa43/0xd00
[ 524.395832] tty_ioctl+0x3e7/0x910
[ 524.397041] ? trace_hardirqs_on_caller+0xe7/0x180
[ 524.398512] do_vfs_ioctl+0x8a/0x650
[ 524.399666] ? syscall_trace_enter+0x19e/0x250
[ 524.400977] ksys_ioctl+0x6b/0x80
[ 524.402102] __x64_sys_ioctl+0x11/0x20
[ 524.403327] do_syscall_64+0x4f/0x1f0
[ 524.404494] entry_SYSCALL_64_after_hwframe+0x49/0xbe

[ 524.660246] 7 locks held by a.out/4052:
[ 524.661533] #0: 00000000eb1b6dd2 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x1f/0x50
[ 524.663752] #1: 000000005920aabb (&o_tty->termios_rwsem/1){++++}, at: n_tty_receive_buf_common+0x43/0xd00
[ 524.666284] #2: 00000000fc85438a (&serio->lock){-.-.}, at: serio_interrupt+0x1f/0x80
[ 524.668422] #3: 00000000806da945 (&(&dev->event_lock)->rlock){-.-.}, at: input_event+0x32/0x60
[ 524.670712] #4: 000000005906d89a (rcu_read_lock){....}, at: input_pass_values.part.2+0x0/0x260
[ 524.673017] #5: 000000005906d89a (rcu_read_lock){....}, at: __handle_sysrq+0x0/0x200
[ 524.675144] #6: 00000000ed0ed6ec (tasklist_lock){.?.+}, at: debug_show_all_locks+0x37/0x190



[ 122.170234] a.out R running task 0 2818 1 0x80000084
[ 122.172442] Call Trace:
[ 122.173402] <IRQ>
[ 122.174271] sched_show_task+0x16b/0x230
[ 122.175512] show_state_filter+0x9d/0x190
[ 122.176693] sysrq_handle_showstate+0x7/0x10
[ 122.177924] __handle_sysrq+0x123/0x200
[ 122.179122] sysrq_filter+0x356/0x390
[ 122.180237] input_to_handler+0x4b/0xf0
[ 122.181385] input_pass_values.part.2+0x1ba/0x260
[ 122.182769] input_handle_event+0x11a/0x4f0
[ 122.184131] input_event+0x45/0x60
[ 122.185191] atkbd_interrupt+0x41a/0x6f0
[ 122.186350] serio_interrupt+0x3b/0x80
[ 122.187502] i8042_interrupt+0x1e8/0x3a0
[ 122.188668] __handle_irq_event_percpu+0x5b/0xc0
[ 122.189966] handle_irq_event_percpu+0x1b/0x50
[ 122.191384] handle_irq_event+0x2f/0x50
[ 122.192522] handle_edge_irq+0xcc/0x1a0
[ 122.193679] handle_irq+0x11/0x20
[ 122.194754] do_IRQ+0x52/0x100
[ 122.195764] common_interrupt+0xf/0xf
[ 122.196875] RIP: 0010:__do_softirq+0xa0/0x233
[ 122.198102] RSP: 0018:ffff88013fc03f68 EFLAGS: 00000202 ORIG_RAX: ffffffffffffffd3
[ 122.200212] RAX: ffff8801379bad80 RBX: 00000000ffffffff RCX: 0000000000000000
[ 122.202019] RDX: 0000000000000d84 RSI: ffff8801379bb5b8 RDI: ffff8801379bad80
[ 122.203886] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[ 122.205670] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 122.207536] R13: 0000000000000000 R14: 0000000000000002 R15: 0000000000000000
[ 122.209307] ? common_interrupt+0xa/0xf
[ 122.210533] ? __do_softirq+0x9a/0x233
[ 122.211711] ? clockevents_program_event+0x76/0xe0
[ 122.213047] irq_exit+0xdc/0xe0
[ 122.214156] smp_apic_timer_interrupt+0x4d/0x80
[ 122.215446] apic_timer_interrupt+0xf/0x20
[ 122.216671] </IRQ>
[ 122.217497] RIP: 0010:echo_char+0x29/0x90
[ 122.218744] RSP: 0018:ffffc90006787d00 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
[ 122.220616] RAX: ffffc90006959000 RBX: ffffc90006959000 RCX: 000000019b8c0c19
[ 122.222449] RDX: 0000000000000000 RSI: ffff880138ee1800 RDI: 0000000000000000
[ 122.224247] RBP: ffff880138ee1800 R08: 0000000000000012 R09: 0000000000000000
[ 122.226116] R10: 0000000000000000 R11: ffffffff814184f3 R12: 0000000000000012
[ 122.227921] R13: ffff880138ee1800 R14: 00000000d59f6933 R15: 0000000000000012
[ 122.229862] ? n_tty_receive_buf_common+0x43/0xd00
[ 122.231235] n_tty_receive_char_special+0x4ea/0xad0
[ 122.232622] ? n_tty_receive_buf_common+0x43/0xd00
[ 122.234084] n_tty_receive_buf_common+0xa43/0xd00
[ 122.235449] tty_ioctl+0x3e7/0x910
[ 122.236565] ? trace_hardirqs_on_caller+0xe7/0x180
[ 122.237993] do_vfs_ioctl+0x8a/0x650
[ 122.239157] ? syscall_trace_enter+0x19e/0x250
[ 122.240467] ksys_ioctl+0x6b/0x80
[ 122.241633] __x64_sys_ioctl+0x11/0x20
[ 122.242809] do_syscall_64+0x4f/0x1f0
[ 122.243969] entry_SYSCALL_64_after_hwframe+0x49/0xbe

[ 122.624858] 7 locks held by a.out/2818:
[ 122.626110] #0: 00000000d2e12ac0 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x1f/0x50
[ 122.628238] #1: 00000000c1852a2e (&o_tty->termios_rwsem/1){++++}, at: n_tty_receive_buf_common+0x43/0xd00
[ 122.630579] #2: 00000000019e0dd4 (&serio->lock){-.-.}, at: serio_interrupt+0x1f/0x80
[ 122.632634] #3: 00000000165952ed (&(&dev->event_lock)->rlock){-.-.}, at: input_event+0x32/0x60
[ 122.634823] #4: 0000000013aedeb2 (rcu_read_lock){....}, at: input_pass_values.part.2+0x0/0x260
[ 122.637122] #5: 0000000013aedeb2 (rcu_read_lock){....}, at: __handle_sysrq+0x0/0x200
[ 122.639133] #6: 0000000094121093 (tasklist_lock){.?.+}, at: debug_show_all_locks+0x37/0x190



[ 701.099036] a.out D 0 4365 1 0x80000082
[ 701.100533] Call Trace:
[ 701.101735] ? __schedule+0x278/0x750
[ 701.103178] ? _raw_spin_unlock_irq+0x24/0x40
[ 701.104611] schedule+0x34/0x80
[ 701.105755] rwsem_down_write_failed+0x10a/0x230
[ 701.107228] ? call_rwsem_down_write_failed+0x13/0x20
[ 701.108781] call_rwsem_down_write_failed+0x13/0x20
[ 701.110544] ? n_tty_flush_buffer+0x14/0x50
[ 701.111905] down_write+0x3b/0x50
[ 701.113148] ? n_tty_flush_buffer+0x14/0x50
[ 701.114550] n_tty_flush_buffer+0x14/0x50
[ 701.115962] tty_ldisc_hangup+0x2a/0x1d0
[ 701.117270] __tty_hangup+0x13f/0x2b0
[ 701.118820] tty_release+0xf0/0x500
[ 701.120450] ? lock_acquire+0x43/0x60
[ 701.122099] __fput+0x95/0x1d0
[ 701.123377] task_work_run+0x84/0xa0
[ 701.124632] do_exit+0x2cc/0xac0
[ 701.125713] ? syscall_trace_enter+0x19e/0x250
[ 701.127039] do_group_exit+0x38/0xb0
[ 701.128469] __x64_sys_exit_group+0xf/0x10
[ 701.129795] do_syscall_64+0x4f/0x1f0
[ 701.130946] entry_SYSCALL_64_after_hwframe+0x49/0xbe

[ 701.635816] 4 locks held by a.out/4365:
[ 701.637551] #0: 0000000051b314cc (&tty->legacy_mutex){+.+.}, at: tty_release+0x4d/0x500
[ 701.639958] #1: 00000000fcddaa23 (&tty->legacy_mutex/1){+.+.}, at: __tty_hangup+0x5c/0x2b0
[ 701.642259] #2: 000000005a4dd91b (&tty->ldisc_sem){++++}, at: tty_ldisc_ref+0x15/0x50
[ 701.645185] #3: 00000000997a5bc4 (&o_tty->termios_rwsem/1){++++}, at: n_tty_flush_buffer+0x14/0x50



[ 264.159739] a.out R running task 0 8464 1 0x80000084
[ 264.159739] Call Trace:
[ 264.159739] <IRQ>
[ 264.159739] sched_show_task+0x16b/0x230
[ 264.159739] show_state_filter+0x9d/0x190
[ 264.159739] sysrq_handle_showstate+0x7/0x10
[ 264.159739] __handle_sysrq+0x123/0x200
[ 264.159739] sysrq_filter+0x356/0x390
[ 264.159739] input_to_handler+0x4b/0xf0
[ 264.159739] input_pass_values.part.2+0x1ba/0x260
[ 264.159739] input_handle_event+0x11a/0x4f0
[ 264.159739] input_event+0x45/0x60
[ 264.159739] atkbd_interrupt+0x41a/0x6f0
[ 264.159739] serio_interrupt+0x3b/0x80
[ 264.159739] i8042_interrupt+0x1e8/0x3a0
[ 264.159739] ? _raw_spin_unlock_irq+0x24/0x40
[ 264.159739] __handle_irq_event_percpu+0x5b/0xc0
[ 264.159739] handle_irq_event_percpu+0x1b/0x50
[ 264.159739] handle_irq_event+0x2f/0x50
[ 264.159739] handle_edge_irq+0xcc/0x1a0
[ 264.159739] handle_irq+0x11/0x20
[ 264.159739] do_IRQ+0x52/0x100
[ 264.159739] common_interrupt+0xf/0xf
[ 264.159739] </IRQ>
[ 264.159739] RIP: 0010:__process_echoes+0xc4/0x260
[ 264.159739] RSP: 0018:ffffc90003257d18 EFLAGS: 00000296 ORIG_RAX: ffffffffffffffd3
[ 264.159739] RAX: 0000000000000004 RBX: 00000009abab4dd2 RCX: 00000009abab4dce
[ 264.159739] RDX: fffffff65454b232 RSI: ffff880137fed800 RDI: 0000000000000000
[ 264.159739] RBP: ffffc90003305000 R08: 0000000000000000 R09: 0000000000000001
[ 264.159739] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 264.159739] R13: ffff880137fed800 R14: 0000000000001f00 R15: 0000000000000000
[ 264.159739] ? __process_echoes+0x14c/0x260
[ 264.159739] n_tty_receive_buf_common+0x4b6/0xd00
[ 264.159739] tty_ioctl+0x3e7/0x910
[ 264.159739] ? trace_hardirqs_on_caller+0xe7/0x180
[ 264.159739] do_vfs_ioctl+0x8a/0x650
[ 264.159739] ? syscall_trace_enter+0x19e/0x250
[ 264.159739] ksys_ioctl+0x6b/0x80
[ 264.159739] __x64_sys_ioctl+0x11/0x20
[ 264.159739] do_syscall_64+0x4f/0x1f0
[ 264.159739] entry_SYSCALL_64_after_hwframe+0x49/0xbe

[ 264.159739] 8 locks held by a.out/8464:
[ 264.159739] #0: 000000000a54adcf (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x1f/0x50
[ 264.159739] #1: 000000002abad3ab (&o_tty->termios_rwsem/1){++++}, at: n_tty_receive_buf_common+0x43/0xd00
[ 264.159739] #2: 00000000705a196b (&ldata->output_lock){+.+.}, at: n_tty_receive_buf_common+0x4a4/0xd00
[ 264.159739] #3: 000000008434776a (&serio->lock){-.-.}, at: serio_interrupt+0x1f/0x80
[ 264.159739] #4: 00000000710258a9 (&(&dev->event_lock)->rlock){-.-.}, at: input_event+0x32/0x60
[ 264.159739] #5: 000000004b5299a2 (rcu_read_lock){....}, at: input_pass_values.part.2+0x0/0x260
[ 264.159739] #6: 000000004b5299a2 (rcu_read_lock){....}, at: __handle_sysrq+0x0/0x200
[ 264.159739] #7: 00000000082c04ee (tasklist_lock){.?.+}, at: debug_show_all_locks+0x37/0x190

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