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![Will Deacon](/assets/img/avatar_default.png)
commit 20bb759a66
upstream.
Calling 'panic()' on a kernel with CONFIG_PREEMPT=y can leave the
calling CPU in an infinite loop, but with interrupts and preemption
enabled. From this state, userspace can continue to be scheduled,
despite the system being "dead" as far as the kernel is concerned.
This is easily reproducible on arm64 when booting with "nosmp" on the
command line; a couple of shell scripts print out a periodic "Ping"
message whilst another triggers a crash by writing to
/proc/sysrq-trigger:
| sysrq: Trigger a crash
| Kernel panic - not syncing: sysrq triggered crash
| CPU: 0 PID: 1 Comm: init Not tainted 5.2.15 #1
| Hardware name: linux,dummy-virt (DT)
| Call trace:
| dump_backtrace+0x0/0x148
| show_stack+0x14/0x20
| dump_stack+0xa0/0xc4
| panic+0x140/0x32c
| sysrq_handle_reboot+0x0/0x20
| __handle_sysrq+0x124/0x190
| write_sysrq_trigger+0x64/0x88
| proc_reg_write+0x60/0xa8
| __vfs_write+0x18/0x40
| vfs_write+0xa4/0x1b8
| ksys_write+0x64/0xf0
| __arm64_sys_write+0x14/0x20
| el0_svc_common.constprop.0+0xb0/0x168
| el0_svc_handler+0x28/0x78
| el0_svc+0x8/0xc
| Kernel Offset: disabled
| CPU features: 0x0002,24002004
| Memory Limit: none
| ---[ end Kernel panic - not syncing: sysrq triggered crash ]---
| Ping 2!
| Ping 1!
| Ping 1!
| Ping 2!
The issue can also be triggered on x86 kernels if CONFIG_SMP=n,
otherwise local interrupts are disabled in 'smp_send_stop()'.
Disable preemption in 'panic()' before re-enabling interrupts.
Link: http://lkml.kernel.org/r/20191002123538.22609-1-will@kernel.org
Link: https://lore.kernel.org/r/BX1W47JXPMR8.58IYW53H6M5N@dragonstone
Signed-off-by: Will Deacon <will@kernel.org>
Reported-by: Xogium <contact@xogium.me>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
634 lines
16 KiB
C
634 lines
16 KiB
C
/*
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* linux/kernel/panic.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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/*
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* This function is used through-out the kernel (including mm and fs)
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* to indicate a major problem.
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*/
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#include <linux/debug_locks.h>
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#include <linux/sched/debug.h>
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#include <linux/interrupt.h>
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#include <linux/kmsg_dump.h>
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#include <linux/kallsyms.h>
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#include <linux/notifier.h>
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#include <linux/vt_kern.h>
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#include <linux/module.h>
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#include <linux/random.h>
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#include <linux/ftrace.h>
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#include <linux/reboot.h>
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#include <linux/delay.h>
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#include <linux/kexec.h>
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#include <linux/sched.h>
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#include <linux/sysrq.h>
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#include <linux/init.h>
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#include <linux/nmi.h>
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#include <linux/console.h>
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#include <linux/bug.h>
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#include <linux/ratelimit.h>
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#define PANIC_TIMER_STEP 100
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#define PANIC_BLINK_SPD 18
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int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE;
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static unsigned long tainted_mask;
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static int pause_on_oops;
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static int pause_on_oops_flag;
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static DEFINE_SPINLOCK(pause_on_oops_lock);
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bool crash_kexec_post_notifiers;
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int panic_on_warn __read_mostly;
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int panic_timeout = CONFIG_PANIC_TIMEOUT;
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EXPORT_SYMBOL_GPL(panic_timeout);
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ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
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EXPORT_SYMBOL(panic_notifier_list);
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static long no_blink(int state)
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{
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return 0;
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}
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/* Returns how long it waited in ms */
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long (*panic_blink)(int state);
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EXPORT_SYMBOL(panic_blink);
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/*
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* Stop ourself in panic -- architecture code may override this
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*/
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void __weak panic_smp_self_stop(void)
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{
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while (1)
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cpu_relax();
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}
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/*
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* Stop ourselves in NMI context if another CPU has already panicked. Arch code
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* may override this to prepare for crash dumping, e.g. save regs info.
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*/
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void __weak nmi_panic_self_stop(struct pt_regs *regs)
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{
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panic_smp_self_stop();
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}
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/*
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* Stop other CPUs in panic. Architecture dependent code may override this
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* with more suitable version. For example, if the architecture supports
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* crash dump, it should save registers of each stopped CPU and disable
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* per-CPU features such as virtualization extensions.
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*/
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void __weak crash_smp_send_stop(void)
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{
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static int cpus_stopped;
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/*
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* This function can be called twice in panic path, but obviously
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* we execute this only once.
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*/
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if (cpus_stopped)
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return;
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/*
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* Note smp_send_stop is the usual smp shutdown function, which
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* unfortunately means it may not be hardened to work in a panic
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* situation.
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*/
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smp_send_stop();
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cpus_stopped = 1;
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}
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atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
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/*
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* A variant of panic() called from NMI context. We return if we've already
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* panicked on this CPU. If another CPU already panicked, loop in
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* nmi_panic_self_stop() which can provide architecture dependent code such
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* as saving register state for crash dump.
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*/
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void nmi_panic(struct pt_regs *regs, const char *msg)
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{
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int old_cpu, cpu;
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cpu = raw_smp_processor_id();
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old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu);
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if (old_cpu == PANIC_CPU_INVALID)
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panic("%s", msg);
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else if (old_cpu != cpu)
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nmi_panic_self_stop(regs);
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}
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EXPORT_SYMBOL(nmi_panic);
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/**
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* panic - halt the system
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* @fmt: The text string to print
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*
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* Display a message, then perform cleanups.
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*
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* This function never returns.
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*/
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void panic(const char *fmt, ...)
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{
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static char buf[1024];
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va_list args;
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long i, i_next = 0;
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int state = 0;
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int old_cpu, this_cpu;
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bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
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/*
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* Disable local interrupts. This will prevent panic_smp_self_stop
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* from deadlocking the first cpu that invokes the panic, since
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* there is nothing to prevent an interrupt handler (that runs
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* after setting panic_cpu) from invoking panic() again.
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*/
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local_irq_disable();
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preempt_disable_notrace();
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/*
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* It's possible to come here directly from a panic-assertion and
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* not have preempt disabled. Some functions called from here want
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* preempt to be disabled. No point enabling it later though...
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*
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* Only one CPU is allowed to execute the panic code from here. For
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* multiple parallel invocations of panic, all other CPUs either
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* stop themself or will wait until they are stopped by the 1st CPU
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* with smp_send_stop().
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*
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* `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which
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* comes here, so go ahead.
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* `old_cpu == this_cpu' means we came from nmi_panic() which sets
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* panic_cpu to this CPU. In this case, this is also the 1st CPU.
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*/
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this_cpu = raw_smp_processor_id();
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old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
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if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
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panic_smp_self_stop();
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console_verbose();
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bust_spinlocks(1);
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va_start(args, fmt);
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vsnprintf(buf, sizeof(buf), fmt, args);
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va_end(args);
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pr_emerg("Kernel panic - not syncing: %s\n", buf);
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#ifdef CONFIG_DEBUG_BUGVERBOSE
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/*
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* Avoid nested stack-dumping if a panic occurs during oops processing
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*/
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if (!test_taint(TAINT_DIE) && oops_in_progress <= 1)
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dump_stack();
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#endif
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/*
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* If we have crashed and we have a crash kernel loaded let it handle
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* everything else.
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* If we want to run this after calling panic_notifiers, pass
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* the "crash_kexec_post_notifiers" option to the kernel.
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*
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* Bypass the panic_cpu check and call __crash_kexec directly.
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*/
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if (!_crash_kexec_post_notifiers) {
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printk_safe_flush_on_panic();
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__crash_kexec(NULL);
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/*
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* Note smp_send_stop is the usual smp shutdown function, which
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* unfortunately means it may not be hardened to work in a
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* panic situation.
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*/
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smp_send_stop();
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} else {
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/*
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* If we want to do crash dump after notifier calls and
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* kmsg_dump, we will need architecture dependent extra
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* works in addition to stopping other CPUs.
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*/
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crash_smp_send_stop();
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}
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/*
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* Run any panic handlers, including those that might need to
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* add information to the kmsg dump output.
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*/
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atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
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/* Call flush even twice. It tries harder with a single online CPU */
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printk_safe_flush_on_panic();
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kmsg_dump(KMSG_DUMP_PANIC);
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/*
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* If you doubt kdump always works fine in any situation,
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* "crash_kexec_post_notifiers" offers you a chance to run
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* panic_notifiers and dumping kmsg before kdump.
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* Note: since some panic_notifiers can make crashed kernel
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* more unstable, it can increase risks of the kdump failure too.
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*
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* Bypass the panic_cpu check and call __crash_kexec directly.
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*/
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if (_crash_kexec_post_notifiers)
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__crash_kexec(NULL);
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#ifdef CONFIG_VT
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unblank_screen();
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#endif
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console_unblank();
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/*
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* We may have ended up stopping the CPU holding the lock (in
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* smp_send_stop()) while still having some valuable data in the console
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* buffer. Try to acquire the lock then release it regardless of the
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* result. The release will also print the buffers out. Locks debug
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* should be disabled to avoid reporting bad unlock balance when
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* panic() is not being callled from OOPS.
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*/
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debug_locks_off();
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console_flush_on_panic();
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if (!panic_blink)
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panic_blink = no_blink;
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if (panic_timeout > 0) {
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/*
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* Delay timeout seconds before rebooting the machine.
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* We can't use the "normal" timers since we just panicked.
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*/
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pr_emerg("Rebooting in %d seconds..\n", panic_timeout);
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for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) {
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touch_nmi_watchdog();
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if (i >= i_next) {
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i += panic_blink(state ^= 1);
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i_next = i + 3600 / PANIC_BLINK_SPD;
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}
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mdelay(PANIC_TIMER_STEP);
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}
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}
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if (panic_timeout != 0) {
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/*
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* This will not be a clean reboot, with everything
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* shutting down. But if there is a chance of
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* rebooting the system it will be rebooted.
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*/
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emergency_restart();
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}
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#ifdef __sparc__
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{
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extern int stop_a_enabled;
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/* Make sure the user can actually press Stop-A (L1-A) */
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stop_a_enabled = 1;
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pr_emerg("Press Stop-A (L1-A) from sun keyboard or send break\n"
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"twice on console to return to the boot prom\n");
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}
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#endif
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#if defined(CONFIG_S390)
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{
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unsigned long caller;
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caller = (unsigned long)__builtin_return_address(0);
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disabled_wait(caller);
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}
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#endif
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pr_emerg("---[ end Kernel panic - not syncing: %s\n", buf);
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local_irq_enable();
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for (i = 0; ; i += PANIC_TIMER_STEP) {
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touch_softlockup_watchdog();
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if (i >= i_next) {
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i += panic_blink(state ^= 1);
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i_next = i + 3600 / PANIC_BLINK_SPD;
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}
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mdelay(PANIC_TIMER_STEP);
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}
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}
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EXPORT_SYMBOL(panic);
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/*
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* TAINT_FORCED_RMMOD could be a per-module flag but the module
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* is being removed anyway.
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*/
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const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
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{ 'P', 'G', true }, /* TAINT_PROPRIETARY_MODULE */
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{ 'F', ' ', true }, /* TAINT_FORCED_MODULE */
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{ 'S', ' ', false }, /* TAINT_CPU_OUT_OF_SPEC */
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{ 'R', ' ', false }, /* TAINT_FORCED_RMMOD */
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{ 'M', ' ', false }, /* TAINT_MACHINE_CHECK */
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{ 'B', ' ', false }, /* TAINT_BAD_PAGE */
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{ 'U', ' ', false }, /* TAINT_USER */
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{ 'D', ' ', false }, /* TAINT_DIE */
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{ 'A', ' ', false }, /* TAINT_OVERRIDDEN_ACPI_TABLE */
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{ 'W', ' ', false }, /* TAINT_WARN */
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{ 'C', ' ', true }, /* TAINT_CRAP */
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{ 'I', ' ', false }, /* TAINT_FIRMWARE_WORKAROUND */
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{ 'O', ' ', true }, /* TAINT_OOT_MODULE */
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{ 'E', ' ', true }, /* TAINT_UNSIGNED_MODULE */
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{ 'L', ' ', false }, /* TAINT_SOFTLOCKUP */
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{ 'K', ' ', true }, /* TAINT_LIVEPATCH */
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};
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/**
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* print_tainted - return a string to represent the kernel taint state.
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*
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* 'P' - Proprietary module has been loaded.
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* 'F' - Module has been forcibly loaded.
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* 'S' - SMP with CPUs not designed for SMP.
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* 'R' - User forced a module unload.
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* 'M' - System experienced a machine check exception.
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* 'B' - System has hit bad_page.
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* 'U' - Userspace-defined naughtiness.
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* 'D' - Kernel has oopsed before
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* 'A' - ACPI table overridden.
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* 'W' - Taint on warning.
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* 'C' - modules from drivers/staging are loaded.
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* 'I' - Working around severe firmware bug.
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* 'O' - Out-of-tree module has been loaded.
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* 'E' - Unsigned module has been loaded.
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* 'L' - A soft lockup has previously occurred.
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* 'K' - Kernel has been live patched.
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*
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* The string is overwritten by the next call to print_tainted().
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*/
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const char *print_tainted(void)
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{
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static char buf[TAINT_FLAGS_COUNT + sizeof("Tainted: ")];
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if (tainted_mask) {
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char *s;
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int i;
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s = buf + sprintf(buf, "Tainted: ");
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for (i = 0; i < TAINT_FLAGS_COUNT; i++) {
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const struct taint_flag *t = &taint_flags[i];
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*s++ = test_bit(i, &tainted_mask) ?
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t->c_true : t->c_false;
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}
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*s = 0;
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} else
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snprintf(buf, sizeof(buf), "Not tainted");
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return buf;
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}
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int test_taint(unsigned flag)
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{
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return test_bit(flag, &tainted_mask);
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}
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EXPORT_SYMBOL(test_taint);
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unsigned long get_taint(void)
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{
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return tainted_mask;
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}
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/**
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* add_taint: add a taint flag if not already set.
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* @flag: one of the TAINT_* constants.
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* @lockdep_ok: whether lock debugging is still OK.
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*
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* If something bad has gone wrong, you'll want @lockdebug_ok = false, but for
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* some notewortht-but-not-corrupting cases, it can be set to true.
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*/
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void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
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{
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if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && __debug_locks_off())
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pr_warn("Disabling lock debugging due to kernel taint\n");
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set_bit(flag, &tainted_mask);
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}
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EXPORT_SYMBOL(add_taint);
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static void spin_msec(int msecs)
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{
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int i;
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for (i = 0; i < msecs; i++) {
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touch_nmi_watchdog();
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mdelay(1);
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}
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}
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/*
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* It just happens that oops_enter() and oops_exit() are identically
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* implemented...
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*/
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static void do_oops_enter_exit(void)
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{
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unsigned long flags;
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static int spin_counter;
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if (!pause_on_oops)
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return;
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spin_lock_irqsave(&pause_on_oops_lock, flags);
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if (pause_on_oops_flag == 0) {
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/* This CPU may now print the oops message */
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pause_on_oops_flag = 1;
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} else {
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/* We need to stall this CPU */
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if (!spin_counter) {
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/* This CPU gets to do the counting */
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spin_counter = pause_on_oops;
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do {
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spin_unlock(&pause_on_oops_lock);
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spin_msec(MSEC_PER_SEC);
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spin_lock(&pause_on_oops_lock);
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} while (--spin_counter);
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pause_on_oops_flag = 0;
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} else {
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/* This CPU waits for a different one */
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while (spin_counter) {
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spin_unlock(&pause_on_oops_lock);
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spin_msec(1);
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spin_lock(&pause_on_oops_lock);
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}
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}
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}
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spin_unlock_irqrestore(&pause_on_oops_lock, flags);
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}
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|
|
/*
|
|
* Return true if the calling CPU is allowed to print oops-related info.
|
|
* This is a bit racy..
|
|
*/
|
|
int oops_may_print(void)
|
|
{
|
|
return pause_on_oops_flag == 0;
|
|
}
|
|
|
|
/*
|
|
* Called when the architecture enters its oops handler, before it prints
|
|
* anything. If this is the first CPU to oops, and it's oopsing the first
|
|
* time then let it proceed.
|
|
*
|
|
* This is all enabled by the pause_on_oops kernel boot option. We do all
|
|
* this to ensure that oopses don't scroll off the screen. It has the
|
|
* side-effect of preventing later-oopsing CPUs from mucking up the display,
|
|
* too.
|
|
*
|
|
* It turns out that the CPU which is allowed to print ends up pausing for
|
|
* the right duration, whereas all the other CPUs pause for twice as long:
|
|
* once in oops_enter(), once in oops_exit().
|
|
*/
|
|
void oops_enter(void)
|
|
{
|
|
tracing_off();
|
|
/* can't trust the integrity of the kernel anymore: */
|
|
debug_locks_off();
|
|
do_oops_enter_exit();
|
|
}
|
|
|
|
/*
|
|
* 64-bit random ID for oopses:
|
|
*/
|
|
static u64 oops_id;
|
|
|
|
static int init_oops_id(void)
|
|
{
|
|
if (!oops_id)
|
|
get_random_bytes(&oops_id, sizeof(oops_id));
|
|
else
|
|
oops_id++;
|
|
|
|
return 0;
|
|
}
|
|
late_initcall(init_oops_id);
|
|
|
|
void print_oops_end_marker(void)
|
|
{
|
|
init_oops_id();
|
|
pr_warn("---[ end trace %016llx ]---\n", (unsigned long long)oops_id);
|
|
}
|
|
|
|
/*
|
|
* Called when the architecture exits its oops handler, after printing
|
|
* everything.
|
|
*/
|
|
void oops_exit(void)
|
|
{
|
|
do_oops_enter_exit();
|
|
print_oops_end_marker();
|
|
kmsg_dump(KMSG_DUMP_OOPS);
|
|
}
|
|
|
|
struct warn_args {
|
|
const char *fmt;
|
|
va_list args;
|
|
};
|
|
|
|
void __warn(const char *file, int line, void *caller, unsigned taint,
|
|
struct pt_regs *regs, struct warn_args *args)
|
|
{
|
|
disable_trace_on_warning();
|
|
|
|
pr_warn("------------[ cut here ]------------\n");
|
|
|
|
if (file)
|
|
pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
|
|
raw_smp_processor_id(), current->pid, file, line,
|
|
caller);
|
|
else
|
|
pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
|
|
raw_smp_processor_id(), current->pid, caller);
|
|
|
|
if (args)
|
|
vprintk(args->fmt, args->args);
|
|
|
|
if (panic_on_warn) {
|
|
/*
|
|
* This thread may hit another WARN() in the panic path.
|
|
* Resetting this prevents additional WARN() from panicking the
|
|
* system on this thread. Other threads are blocked by the
|
|
* panic_mutex in panic().
|
|
*/
|
|
panic_on_warn = 0;
|
|
panic("panic_on_warn set ...\n");
|
|
}
|
|
|
|
print_modules();
|
|
|
|
if (regs)
|
|
show_regs(regs);
|
|
else
|
|
dump_stack();
|
|
|
|
print_oops_end_marker();
|
|
|
|
/* Just a warning, don't kill lockdep. */
|
|
add_taint(taint, LOCKDEP_STILL_OK);
|
|
}
|
|
|
|
#ifdef WANT_WARN_ON_SLOWPATH
|
|
void warn_slowpath_fmt(const char *file, int line, const char *fmt, ...)
|
|
{
|
|
struct warn_args args;
|
|
|
|
args.fmt = fmt;
|
|
va_start(args.args, fmt);
|
|
__warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL,
|
|
&args);
|
|
va_end(args.args);
|
|
}
|
|
EXPORT_SYMBOL(warn_slowpath_fmt);
|
|
|
|
void warn_slowpath_fmt_taint(const char *file, int line,
|
|
unsigned taint, const char *fmt, ...)
|
|
{
|
|
struct warn_args args;
|
|
|
|
args.fmt = fmt;
|
|
va_start(args.args, fmt);
|
|
__warn(file, line, __builtin_return_address(0), taint, NULL, &args);
|
|
va_end(args.args);
|
|
}
|
|
EXPORT_SYMBOL(warn_slowpath_fmt_taint);
|
|
|
|
void warn_slowpath_null(const char *file, int line)
|
|
{
|
|
__warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL, NULL);
|
|
}
|
|
EXPORT_SYMBOL(warn_slowpath_null);
|
|
#endif
|
|
|
|
#ifdef CONFIG_CC_STACKPROTECTOR
|
|
|
|
/*
|
|
* Called when gcc's -fstack-protector feature is used, and
|
|
* gcc detects corruption of the on-stack canary value
|
|
*/
|
|
__visible void __stack_chk_fail(void)
|
|
{
|
|
panic("stack-protector: Kernel stack is corrupted in: %p\n",
|
|
__builtin_return_address(0));
|
|
}
|
|
EXPORT_SYMBOL(__stack_chk_fail);
|
|
|
|
#endif
|
|
|
|
#ifdef CONFIG_ARCH_HAS_REFCOUNT
|
|
void refcount_error_report(struct pt_regs *regs, const char *err)
|
|
{
|
|
WARN_RATELIMIT(1, "refcount_t %s at %pB in %s[%d], uid/euid: %u/%u\n",
|
|
err, (void *)instruction_pointer(regs),
|
|
current->comm, task_pid_nr(current),
|
|
from_kuid_munged(&init_user_ns, current_uid()),
|
|
from_kuid_munged(&init_user_ns, current_euid()));
|
|
}
|
|
#endif
|
|
|
|
core_param(panic, panic_timeout, int, 0644);
|
|
core_param(pause_on_oops, pause_on_oops, int, 0644);
|
|
core_param(panic_on_warn, panic_on_warn, int, 0644);
|
|
core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644);
|
|
|
|
static int __init oops_setup(char *s)
|
|
{
|
|
if (!s)
|
|
return -EINVAL;
|
|
if (!strcmp(s, "panic"))
|
|
panic_on_oops = 1;
|
|
return 0;
|
|
}
|
|
early_param("oops", oops_setup);
|