diff options
Diffstat (limited to 'kernel/printk')
| -rw-r--r-- | kernel/printk/Makefile | 1 | ||||
| -rw-r--r-- | kernel/printk/internal.h | 57 | ||||
| -rw-r--r-- | kernel/printk/nmi.c | 260 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 31 |
4 files changed, 330 insertions, 19 deletions
diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile index 85405bdcf..abb0042a4 100644 --- a/kernel/printk/Makefile +++ b/kernel/printk/Makefile @@ -1,2 +1,3 @@ obj-y = printk.o +obj-$(CONFIG_PRINTK_NMI) += nmi.o obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h new file mode 100644 index 000000000..7fd2838fa --- /dev/null +++ b/kernel/printk/internal.h @@ -0,0 +1,57 @@ +/* + * internal.h - printk internal definitions + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + */ +#include <linux/percpu.h> + +typedef __printf(1, 0) int (*printk_func_t)(const char *fmt, va_list args); + +int __printf(1, 0) vprintk_default(const char *fmt, va_list args); + +#ifdef CONFIG_PRINTK_NMI + +extern raw_spinlock_t logbuf_lock; + +/* + * printk() could not take logbuf_lock in NMI context. Instead, + * it temporary stores the strings into a per-CPU buffer. + * The alternative implementation is chosen transparently + * via per-CPU variable. + */ +DECLARE_PER_CPU(printk_func_t, printk_func); +static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) +{ + return this_cpu_read(printk_func)(fmt, args); +} + +extern atomic_t nmi_message_lost; +static inline int get_nmi_message_lost(void) +{ + return atomic_xchg(&nmi_message_lost, 0); +} + +#else /* CONFIG_PRINTK_NMI */ + +static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) +{ + return vprintk_default(fmt, args); +} + +static inline int get_nmi_message_lost(void) +{ + return 0; +} + +#endif /* CONFIG_PRINTK_NMI */ diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c new file mode 100644 index 000000000..b69eb8a28 --- /dev/null +++ b/kernel/printk/nmi.c @@ -0,0 +1,260 @@ +/* + * nmi.c - Safe printk in NMI context + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + */ + +#include <linux/preempt.h> +#include <linux/spinlock.h> +#include <linux/debug_locks.h> +#include <linux/smp.h> +#include <linux/cpumask.h> +#include <linux/irq_work.h> +#include <linux/printk.h> + +#include "internal.h" + +/* + * printk() could not take logbuf_lock in NMI context. Instead, + * it uses an alternative implementation that temporary stores + * the strings into a per-CPU buffer. The content of the buffer + * is later flushed into the main ring buffer via IRQ work. + * + * The alternative implementation is chosen transparently + * via @printk_func per-CPU variable. + * + * The implementation allows to flush the strings also from another CPU. + * There are situations when we want to make sure that all buffers + * were handled or when IRQs are blocked. + */ +DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; +static int printk_nmi_irq_ready; +atomic_t nmi_message_lost; + +#define NMI_LOG_BUF_LEN ((1 << CONFIG_NMI_LOG_BUF_SHIFT) - \ + sizeof(atomic_t) - sizeof(struct irq_work)) + +struct nmi_seq_buf { + atomic_t len; /* length of written data */ + struct irq_work work; /* IRQ work that flushes the buffer */ + unsigned char buffer[NMI_LOG_BUF_LEN]; +}; +static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq); + +/* + * Safe printk() for NMI context. It uses a per-CPU buffer to + * store the message. NMIs are not nested, so there is always only + * one writer running. But the buffer might get flushed from another + * CPU, so we need to be careful. + */ +static int vprintk_nmi(const char *fmt, va_list args) +{ + struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq); + int add = 0; + size_t len; + +again: + len = atomic_read(&s->len); + + if (len >= sizeof(s->buffer)) { + atomic_inc(&nmi_message_lost); + return 0; + } + + /* + * Make sure that all old data have been read before the buffer was + * reseted. This is not needed when we just append data. + */ + if (!len) + smp_rmb(); + + add = vsnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args); + + /* + * Do it once again if the buffer has been flushed in the meantime. + * Note that atomic_cmpxchg() is an implicit memory barrier that + * makes sure that the data were written before updating s->len. + */ + if (atomic_cmpxchg(&s->len, len, len + add) != len) + goto again; + + /* Get flushed in a more safe context. */ + if (add && printk_nmi_irq_ready) { + /* Make sure that IRQ work is really initialized. */ + smp_rmb(); + irq_work_queue(&s->work); + } + + return add; +} + +/* + * printk one line from the temporary buffer from @start index until + * and including the @end index. + */ +static void print_nmi_seq_line(struct nmi_seq_buf *s, int start, int end) +{ + const char *buf = s->buffer + start; + + /* + * The buffers are flushed in NMI only on panic. The messages must + * go only into the ring buffer at this stage. Consoles will get + * explicitly called later when a crashdump is not generated. + */ + if (in_nmi()) + printk_deferred("%.*s", (end - start) + 1, buf); + else + printk("%.*s", (end - start) + 1, buf); + +} + +/* + * Flush data from the associated per_CPU buffer. The function + * can be called either via IRQ work or independently. + */ +static void __printk_nmi_flush(struct irq_work *work) +{ + static raw_spinlock_t read_lock = + __RAW_SPIN_LOCK_INITIALIZER(read_lock); + struct nmi_seq_buf *s = container_of(work, struct nmi_seq_buf, work); + unsigned long flags; + size_t len, size; + int i, last_i; + + /* + * The lock has two functions. First, one reader has to flush all + * available message to make the lockless synchronization with + * writers easier. Second, we do not want to mix messages from + * different CPUs. This is especially important when printing + * a backtrace. + */ + raw_spin_lock_irqsave(&read_lock, flags); + + i = 0; +more: + len = atomic_read(&s->len); + + /* + * This is just a paranoid check that nobody has manipulated + * the buffer an unexpected way. If we printed something then + * @len must only increase. + */ + if (i && i >= len) + pr_err("printk_nmi_flush: internal error: i=%d >= len=%zu\n", + i, len); + + if (!len) + goto out; /* Someone else has already flushed the buffer. */ + + /* Make sure that data has been written up to the @len */ + smp_rmb(); + + size = min(len, sizeof(s->buffer)); + last_i = i; + + /* Print line by line. */ + for (; i < size; i++) { + if (s->buffer[i] == '\n') { + print_nmi_seq_line(s, last_i, i); + last_i = i + 1; + } + } + /* Check if there was a partial line. */ + if (last_i < size) { + print_nmi_seq_line(s, last_i, size - 1); + pr_cont("\n"); + } + + /* + * Check that nothing has got added in the meantime and truncate + * the buffer. Note that atomic_cmpxchg() is an implicit memory + * barrier that makes sure that the data were copied before + * updating s->len. + */ + if (atomic_cmpxchg(&s->len, len, 0) != len) + goto more; + +out: + raw_spin_unlock_irqrestore(&read_lock, flags); +} + +/** + * printk_nmi_flush - flush all per-cpu nmi buffers. + * + * The buffers are flushed automatically via IRQ work. This function + * is useful only when someone wants to be sure that all buffers have + * been flushed at some point. + */ +void printk_nmi_flush(void) +{ + int cpu; + + for_each_possible_cpu(cpu) + __printk_nmi_flush(&per_cpu(nmi_print_seq, cpu).work); +} + +/** + * printk_nmi_flush_on_panic - flush all per-cpu nmi buffers when the system + * goes down. + * + * Similar to printk_nmi_flush() but it can be called even in NMI context when + * the system goes down. It does the best effort to get NMI messages into + * the main ring buffer. + * + * Note that it could try harder when there is only one CPU online. + */ +void printk_nmi_flush_on_panic(void) +{ + /* + * Make sure that we could access the main ring buffer. + * Do not risk a double release when more CPUs are up. + */ + if (in_nmi() && raw_spin_is_locked(&logbuf_lock)) { + if (num_online_cpus() > 1) + return; + + debug_locks_off(); + raw_spin_lock_init(&logbuf_lock); + } + + printk_nmi_flush(); +} + +void __init printk_nmi_init(void) +{ + int cpu; + + for_each_possible_cpu(cpu) { + struct nmi_seq_buf *s = &per_cpu(nmi_print_seq, cpu); + + init_irq_work(&s->work, __printk_nmi_flush); + } + + /* Make sure that IRQ works are initialized before enabling. */ + smp_wmb(); + printk_nmi_irq_ready = 1; + + /* Flush pending messages that did not have scheduled IRQ works. */ + printk_nmi_flush(); +} + +void printk_nmi_enter(void) +{ + this_cpu_write(printk_func, vprintk_nmi); +} + +void printk_nmi_exit(void) +{ + this_cpu_write(printk_func, vprintk_default); +} diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 378075fe3..3e8d47ee9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -56,6 +56,7 @@ #include "console_cmdline.h" #include "braille.h" +#include "internal.h" int console_printk[4] = { CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */ @@ -245,7 +246,7 @@ __packed __aligned(4) * within the scheduler's rq lock. It must be released before calling * console_unlock() or anything else that might wake up a process. */ -static DEFINE_RAW_SPINLOCK(logbuf_lock); +DEFINE_RAW_SPINLOCK(logbuf_lock); #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); @@ -1631,6 +1632,7 @@ asmlinkage int vprintk_emit(int facility, int level, unsigned long flags; int this_cpu; int printed_len = 0; + int nmi_message_lost; bool in_sched = false; /* cpu currently holding logbuf_lock in this function */ static unsigned int logbuf_cpu = UINT_MAX; @@ -1681,6 +1683,15 @@ asmlinkage int vprintk_emit(int facility, int level, strlen(recursion_msg)); } + nmi_message_lost = get_nmi_message_lost(); + if (unlikely(nmi_message_lost)) { + text_len = scnprintf(textbuf, sizeof(textbuf), + "BAD LUCK: lost %d message(s) from NMI context!", + nmi_message_lost); + printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0, + NULL, 0, textbuf, text_len); + } + /* * The printf needs to come first; we need the syslog * prefix which might be passed-in as a parameter. @@ -1822,14 +1833,6 @@ int vprintk_default(const char *fmt, va_list args) } EXPORT_SYMBOL_GPL(vprintk_default); -/* - * This allows printk to be diverted to another function per cpu. - * This is useful for calling printk functions from within NMI - * without worrying about race conditions that can lock up the - * box. - */ -DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; - /** * printk - print a kernel message * @fmt: format string @@ -1853,21 +1856,11 @@ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; */ asmlinkage __visible int printk(const char *fmt, ...) { - printk_func_t vprintk_func; va_list args; int r; va_start(args, fmt); - - /* - * If a caller overrides the per_cpu printk_func, then it needs - * to disable preemption when calling printk(). Otherwise - * the printk_func should be set to the default. No need to - * disable preemption here. - */ - vprintk_func = this_cpu_read(printk_func); r = vprintk_func(fmt, args); - va_end(args); return r; |