| 1 | |
| 2 | |
| 3 | * printk_safe.c - Safe printk for printk-deadlock-prone contexts
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| 4 |
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| 5 |
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| 6 | #include <linux/preempt.h>
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| 7 | #include <linux/kdb.h>
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| 8 | #include <linux/smp.h>
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| 9 | #include <linux/cpumask.h>
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| 10 | #include <linux/printk.h>
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| 11 | #include <linux/kprobes.h>
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| 12 |
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| 13 | #include "internal.h"
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| 14 |
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| 15 |
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| 16 | static atomic_t force_con;
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| 17 |
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| 18 | void printk_force_console_enter(void)
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| 19 | {
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| 20 | atomic_inc(&force_con);
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| 21 | }
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| 22 |
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| 23 | void printk_force_console_exit(void)
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| 24 | {
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| 25 | atomic_dec(&force_con);
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| 26 | }
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| 27 |
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| 28 | bool is_printk_force_console(void)
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| 29 | {
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| 30 | return atomic_read(&force_con);
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| 31 | }
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| 32 |
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| 33 | static DEFINE_PER_CPU(int, printk_context);
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| 34 |
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| 35 |
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| 36 | void __printk_safe_enter(void)
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| 37 | {
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| 38 | this_cpu_inc(printk_context);
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| 39 | }
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| 40 |
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| 41 |
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| 42 | void __printk_safe_exit(void)
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| 43 | {
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| 44 | this_cpu_dec(printk_context);
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| 45 | }
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| 46 |
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| 47 | void __printk_deferred_enter(void)
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| 48 | {
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| 49 | cant_migrate();
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| 50 | __printk_safe_enter();
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| 51 | }
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| 52 |
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| 53 | void __printk_deferred_exit(void)
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| 54 | {
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| 55 | cant_migrate();
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| 56 | __printk_safe_exit();
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| 57 | }
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| 58 |
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| 59 | bool is_printk_legacy_deferred(void)
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| 60 | {
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| 61 | |
| 62 | * The per-CPU variable @printk_context can be read safely in any
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| 63 | * context. CPU migration is always disabled when set.
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| 64 | *
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| 65 | * A context holding the printk_cpu_sync must not spin waiting for
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| 66 | * another CPU. For legacy printing, it could be the console_lock
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| 67 | * or the port lock.
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| 68 |
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| 69 | return (force_legacy_kthread() ||
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| 70 | this_cpu_read(printk_context) ||
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| 71 | in_nmi() ||
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| 72 | is_printk_cpu_sync_owner());
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| 73 | }
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| 74 |
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| 75 | asmlinkage int vprintk(const char *fmt, va_list args)
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| 76 | {
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| 77 | #ifdef CONFIG_KGDB_KDB
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| 78 |
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| 79 | if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
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| 80 | return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
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| 81 | #endif
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| 82 | return vprintk_default(fmt, args);
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| 83 | }
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| 84 | EXPORT_SYMBOL(vprintk);
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