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![Petr Mladek](/assets/img/avatar_default.png)
kdb_trap_printk allows to pass normal printk() messages to kdb via vkdb_printk(). For example, it is used to get backtrace using the classic show_stack(), see kdb_show_stack(). vkdb_printf() tries to avoid a potential infinite loop by disabling the trap. But this approach is racy, for example: CPU1 CPU2 vkdb_printf() // assume that kdb_trap_printk == 0 saved_trap_printk = kdb_trap_printk; kdb_trap_printk = 0; kdb_show_stack() kdb_trap_printk++; Problem1: Now, a nested printk() on CPU0 calls vkdb_printf() even when it should have been disabled. It will not cause a deadlock but... // using the outdated saved value: 0 kdb_trap_printk = saved_trap_printk; kdb_trap_printk--; Problem2: Now, kdb_trap_printk == -1 and will stay like this. It means that all messages will get passed to kdb from now on. This patch removes the racy saved_trap_printk handling. Instead, the recursion is prevented by a check for the locked CPU. The solution is still kind of racy. A non-related printk(), from another process, might get trapped by vkdb_printf(). And the wanted printk() might not get trapped because kdb_printf_cpu is assigned. But this problem existed even with the original code. A proper solution would be to get_cpu() before setting kdb_trap_printk and trap messages only from this CPU. I am not sure if it is worth the effort, though. In fact, the race is very theoretical. When kdb is running any of the commands that use kdb_trap_printk there is a single active CPU and the other CPUs should be in a holding pen inside kgdb_cpu_enter(). The only time this is violated is when there is a timeout waiting for the other CPUs to report to the holding pen. Finally, note that the situation is a bit schizophrenic. vkdb_printf() explicitly allows recursion but only from KDB code that calls kdb_printf() directly. On the other hand, the generic printk() recursion is not allowed because it might cause an infinite loop. This is why we could not hide the decision inside vkdb_printf() easily. Link: http://lkml.kernel.org/r/1480412276-16690-4-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek <pmladek@suse.com> Cc: Daniel Thompson <daniel.thompson@linaro.org> Cc: Jason Wessel <jason.wessel@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
221 lines
7.3 KiB
C
221 lines
7.3 KiB
C
#ifndef _KDB_H
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#define _KDB_H
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/*
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* Kernel Debugger Architecture Independent Global Headers
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*
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* Copyright (c) 2000-2007 Silicon Graphics, Inc. All Rights Reserved.
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* Copyright (C) 2000 Stephane Eranian <eranian@hpl.hp.com>
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* Copyright (C) 2009 Jason Wessel <jason.wessel@windriver.com>
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*/
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/* Shifted versions of the command enable bits are be used if the command
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* has no arguments (see kdb_check_flags). This allows commands, such as
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* go, to have different permissions depending upon whether it is called
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* with an argument.
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*/
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#define KDB_ENABLE_NO_ARGS_SHIFT 10
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typedef enum {
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KDB_ENABLE_ALL = (1 << 0), /* Enable everything */
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KDB_ENABLE_MEM_READ = (1 << 1),
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KDB_ENABLE_MEM_WRITE = (1 << 2),
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KDB_ENABLE_REG_READ = (1 << 3),
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KDB_ENABLE_REG_WRITE = (1 << 4),
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KDB_ENABLE_INSPECT = (1 << 5),
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KDB_ENABLE_FLOW_CTRL = (1 << 6),
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KDB_ENABLE_SIGNAL = (1 << 7),
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KDB_ENABLE_REBOOT = (1 << 8),
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/* User exposed values stop here, all remaining flags are
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* exclusively used to describe a commands behaviour.
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*/
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KDB_ENABLE_ALWAYS_SAFE = (1 << 9),
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KDB_ENABLE_MASK = (1 << KDB_ENABLE_NO_ARGS_SHIFT) - 1,
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KDB_ENABLE_ALL_NO_ARGS = KDB_ENABLE_ALL << KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_MEM_READ_NO_ARGS = KDB_ENABLE_MEM_READ
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_MEM_WRITE_NO_ARGS = KDB_ENABLE_MEM_WRITE
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_REG_READ_NO_ARGS = KDB_ENABLE_REG_READ
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_REG_WRITE_NO_ARGS = KDB_ENABLE_REG_WRITE
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_INSPECT_NO_ARGS = KDB_ENABLE_INSPECT
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_FLOW_CTRL_NO_ARGS = KDB_ENABLE_FLOW_CTRL
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_SIGNAL_NO_ARGS = KDB_ENABLE_SIGNAL
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_REBOOT_NO_ARGS = KDB_ENABLE_REBOOT
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_ALWAYS_SAFE_NO_ARGS = KDB_ENABLE_ALWAYS_SAFE
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<< KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_ENABLE_MASK_NO_ARGS = KDB_ENABLE_MASK << KDB_ENABLE_NO_ARGS_SHIFT,
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KDB_REPEAT_NO_ARGS = 0x40000000, /* Repeat the command w/o arguments */
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KDB_REPEAT_WITH_ARGS = 0x80000000, /* Repeat the command with args */
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} kdb_cmdflags_t;
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typedef int (*kdb_func_t)(int, const char **);
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#ifdef CONFIG_KGDB_KDB
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/atomic.h>
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#define KDB_POLL_FUNC_MAX 5
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extern int kdb_poll_idx;
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/*
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* kdb_initial_cpu is initialized to -1, and is set to the cpu
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* number whenever the kernel debugger is entered.
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*/
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extern int kdb_initial_cpu;
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/* Types and messages used for dynamically added kdb shell commands */
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#define KDB_MAXARGS 16 /* Maximum number of arguments to a function */
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/* KDB return codes from a command or internal kdb function */
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#define KDB_NOTFOUND (-1)
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#define KDB_ARGCOUNT (-2)
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#define KDB_BADWIDTH (-3)
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#define KDB_BADRADIX (-4)
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#define KDB_NOTENV (-5)
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#define KDB_NOENVVALUE (-6)
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#define KDB_NOTIMP (-7)
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#define KDB_ENVFULL (-8)
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#define KDB_ENVBUFFULL (-9)
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#define KDB_TOOMANYBPT (-10)
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#define KDB_TOOMANYDBREGS (-11)
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#define KDB_DUPBPT (-12)
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#define KDB_BPTNOTFOUND (-13)
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#define KDB_BADMODE (-14)
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#define KDB_BADINT (-15)
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#define KDB_INVADDRFMT (-16)
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#define KDB_BADREG (-17)
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#define KDB_BADCPUNUM (-18)
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#define KDB_BADLENGTH (-19)
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#define KDB_NOBP (-20)
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#define KDB_BADADDR (-21)
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#define KDB_NOPERM (-22)
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/*
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* kdb_diemsg
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*
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* Contains a pointer to the last string supplied to the
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* kernel 'die' panic function.
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*/
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extern const char *kdb_diemsg;
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#define KDB_FLAG_EARLYKDB (1 << 0) /* set from boot parameter kdb=early */
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#define KDB_FLAG_CATASTROPHIC (1 << 1) /* A catastrophic event has occurred */
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#define KDB_FLAG_CMD_INTERRUPT (1 << 2) /* Previous command was interrupted */
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#define KDB_FLAG_NOIPI (1 << 3) /* Do not send IPIs */
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#define KDB_FLAG_NO_CONSOLE (1 << 5) /* No console is available,
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* kdb is disabled */
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#define KDB_FLAG_NO_VT_CONSOLE (1 << 6) /* No VT console is available, do
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* not use keyboard */
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#define KDB_FLAG_NO_I8042 (1 << 7) /* No i8042 chip is available, do
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* not use keyboard */
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extern int kdb_flags; /* Global flags, see kdb_state for per cpu state */
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extern void kdb_save_flags(void);
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extern void kdb_restore_flags(void);
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#define KDB_FLAG(flag) (kdb_flags & KDB_FLAG_##flag)
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#define KDB_FLAG_SET(flag) ((void)(kdb_flags |= KDB_FLAG_##flag))
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#define KDB_FLAG_CLEAR(flag) ((void)(kdb_flags &= ~KDB_FLAG_##flag))
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/*
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* External entry point for the kernel debugger. The pt_regs
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* at the time of entry are supplied along with the reason for
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* entry to the kernel debugger.
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*/
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typedef enum {
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KDB_REASON_ENTER = 1, /* KDB_ENTER() trap/fault - regs valid */
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KDB_REASON_ENTER_SLAVE, /* KDB_ENTER_SLAVE() trap/fault - regs valid */
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KDB_REASON_BREAK, /* Breakpoint inst. - regs valid */
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KDB_REASON_DEBUG, /* Debug Fault - regs valid */
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KDB_REASON_OOPS, /* Kernel Oops - regs valid */
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KDB_REASON_SWITCH, /* CPU switch - regs valid*/
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KDB_REASON_KEYBOARD, /* Keyboard entry - regs valid */
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KDB_REASON_NMI, /* Non-maskable interrupt; regs valid */
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KDB_REASON_RECURSE, /* Recursive entry to kdb;
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* regs probably valid */
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KDB_REASON_SSTEP, /* Single Step trap. - regs valid */
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KDB_REASON_SYSTEM_NMI, /* In NMI due to SYSTEM cmd; regs valid */
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} kdb_reason_t;
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enum kdb_msgsrc {
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KDB_MSGSRC_INTERNAL, /* direct call to kdb_printf() */
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KDB_MSGSRC_PRINTK, /* trapped from printk() */
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};
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extern int kdb_trap_printk;
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extern int kdb_printf_cpu;
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extern __printf(2, 0) int vkdb_printf(enum kdb_msgsrc src, const char *fmt,
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va_list args);
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extern __printf(1, 2) int kdb_printf(const char *, ...);
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typedef __printf(1, 2) int (*kdb_printf_t)(const char *, ...);
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extern void kdb_init(int level);
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/* Access to kdb specific polling devices */
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typedef int (*get_char_func)(void);
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extern get_char_func kdb_poll_funcs[];
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extern int kdb_get_kbd_char(void);
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static inline
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int kdb_process_cpu(const struct task_struct *p)
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{
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unsigned int cpu = task_cpu(p);
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if (cpu > num_possible_cpus())
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cpu = 0;
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return cpu;
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}
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/* kdb access to register set for stack dumping */
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extern struct pt_regs *kdb_current_regs;
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#ifdef CONFIG_KALLSYMS
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extern const char *kdb_walk_kallsyms(loff_t *pos);
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#else /* ! CONFIG_KALLSYMS */
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static inline const char *kdb_walk_kallsyms(loff_t *pos)
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{
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return NULL;
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}
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#endif /* ! CONFIG_KALLSYMS */
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/* Dynamic kdb shell command registration */
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extern int kdb_register(char *, kdb_func_t, char *, char *, short);
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extern int kdb_register_flags(char *, kdb_func_t, char *, char *,
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short, kdb_cmdflags_t);
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extern int kdb_unregister(char *);
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#else /* ! CONFIG_KGDB_KDB */
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static inline __printf(1, 2) int kdb_printf(const char *fmt, ...) { return 0; }
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static inline void kdb_init(int level) {}
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static inline int kdb_register(char *cmd, kdb_func_t func, char *usage,
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char *help, short minlen) { return 0; }
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static inline int kdb_register_flags(char *cmd, kdb_func_t func, char *usage,
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char *help, short minlen,
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kdb_cmdflags_t flags) { return 0; }
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static inline int kdb_unregister(char *cmd) { return 0; }
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#endif /* CONFIG_KGDB_KDB */
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enum {
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KDB_NOT_INITIALIZED,
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KDB_INIT_EARLY,
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KDB_INIT_FULL,
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};
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extern int kdbgetintenv(const char *, int *);
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extern int kdb_set(int, const char **);
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#endif /* !_KDB_H */
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