linux-kernel - Re: [syzbot] [kernel?] possible deadlock in console_flush

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Date: Wed, 20 Mar 2024 16:04:54 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: syzbot <syzbot+f78380e4eae53c64125c@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
        John Ogness
 <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [syzbot] [kernel?] possible deadlock in console_flush_all (2)

On 2024/03/20 15:56, Alexei Starovoitov wrote:
> This has nothing to do with bpf.
> bpf never calls printk().

Please see the Sample crash report in the dashboard.
bpf program is hitting printk() via report_bug().

-> #0 (console_owner){....}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       console_lock_spinning_enable kernel/printk/printk.c:1873 [inline]
       console_emit_next_record kernel/printk/printk.c:2901 [inline]
       console_flush_all+0x810/0xfd0 kernel/printk/printk.c:2973
       console_unlock+0x13b/0x4d0 kernel/printk/printk.c:3042
       vprintk_emit+0x5a6/0x770 kernel/printk/printk.c:2342
       _printk+0xd5/0x120 kernel/printk/printk.c:2367
       __report_bug lib/bug.c:195 [inline]
       report_bug+0x346/0x500 lib/bug.c:219
       handle_bug+0x3e/0x70 arch/x86/kernel/traps.c:239
       exc_invalid_op+0x1a/0x50 arch/x86/kernel/traps.c:260
       asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:621
       __local_bh_enable_ip+0x1be/0x200 kernel/softirq.c:362
       spin_unlock_bh include/linux/spinlock.h:396 [inline]
       __sock_map_delete net/core/sock_map.c:424 [inline]
       sock_map_delete_elem+0xca/0x140 net/core/sock_map.c:446
       bpf_prog_2c29ac5cdc6b1842+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
       __bpf_prog_run include/linux/filter.h:657 [inline]
       bpf_prog_run include/linux/filter.h:664 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
       bpf_trace_run4+0x25a/0x490 kernel/trace/bpf_trace.c:2422
       trace_sched_switch include/trace/events/sched.h:222 [inline]
       __schedule+0x250b/0x49d0 kernel/sched/core.c:6733
       __schedule_loop kernel/sched/core.c:6813 [inline]
       schedule+0x14b/0x320 kernel/sched/core.c:6828
       ptrace_stop+0x5b4/0x940 kernel/signal.c:2358
       ptrace_do_notify kernel/signal.c:2395 [inline]
       ptrace_notify+0x255/0x380 kernel/signal.c:2407
       ptrace_report_syscall include/linux/ptrace.h:415 [inline]
       ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
       syscall_exit_work+0xbd/0x170 kernel/entry/common.c:167
       syscall_exit_to_user_mode_prepare kernel/entry/common.c:194 [inline]
       __syscall_exit_to_user_mode_work kernel/entry/common.c:199 [inline]
       syscall_exit_to_user_mode+0x273/0x360 kernel/entry/common.c:212
       do_syscall_64+0x10a/0x240 arch/x86/entry/common.c:89
       entry_SYSCALL_64_after_hwframe+0x6d/0x75