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The commit719f6a7040("printk: Use the main logbuf in NMI when logbuf_lock is available") brought back the possible deadlocks in printk() and NMI. The check of logbuf_lock is done only in printk_nmi_enter() to prevent mixed output. But another CPU might take the lock later, enter NMI, and: + Both NMIs might be serialized by yet another lock, for example, the one in nmi_cpu_backtrace(). + The other CPU might get stopped in NMI, see smp_send_stop() in panic(). The only safe solution is to use trylock when storing the message into the main log-buffer. It might cause reordering when some lines go to the main lock buffer directly and others are delayed via the per-CPU buffer. It means that it is not useful in general. This patch replaces the problematic NMI deferred context with NMI direct context. It can be used to mark a code that might produce many messages in NMI and the risk of losing them is more critical than problems with eventual reordering. The context is then used when dumping trace buffers on oops. It was the primary motivation for the original fix. Also the reordering is even smaller issue there because some traces have their own time stamps. Finally, nmi_cpu_backtrace() need not longer be serialized because it will always us the per-CPU buffers again. Fixes:719f6a7040("printk: Use the main logbuf in NMI when logbuf_lock is available") Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20180627142028.11259-1-pmladek@suse.com To: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Petr Mladek <pmladek@suse.com>
80 lines
2.3 KiB
C
80 lines
2.3 KiB
C
/*
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* internal.h - printk internal definitions
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/percpu.h>
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#ifdef CONFIG_PRINTK
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#define PRINTK_SAFE_CONTEXT_MASK 0x3fffffff
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#define PRINTK_NMI_DIRECT_CONTEXT_MASK 0x40000000
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#define PRINTK_NMI_CONTEXT_MASK 0x80000000
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extern raw_spinlock_t logbuf_lock;
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__printf(5, 0)
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int vprintk_store(int facility, int level,
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const char *dict, size_t dictlen,
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const char *fmt, va_list args);
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__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
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__printf(1, 0) int vprintk_deferred(const char *fmt, va_list args);
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__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
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void __printk_safe_enter(void);
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void __printk_safe_exit(void);
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#define printk_safe_enter_irqsave(flags) \
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do { \
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local_irq_save(flags); \
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__printk_safe_enter(); \
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} while (0)
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#define printk_safe_exit_irqrestore(flags) \
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do { \
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__printk_safe_exit(); \
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local_irq_restore(flags); \
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} while (0)
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#define printk_safe_enter_irq() \
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do { \
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local_irq_disable(); \
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__printk_safe_enter(); \
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} while (0)
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#define printk_safe_exit_irq() \
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do { \
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__printk_safe_exit(); \
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local_irq_enable(); \
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} while (0)
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void defer_console_output(void);
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#else
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__printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
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/*
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* In !PRINTK builds we still export logbuf_lock spin_lock, console_sem
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* semaphore and some of console functions (console_unlock()/etc.), so
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* printk-safe must preserve the existing local IRQ guarantees.
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*/
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#define printk_safe_enter_irqsave(flags) local_irq_save(flags)
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#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
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#define printk_safe_enter_irq() local_irq_disable()
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#define printk_safe_exit_irq() local_irq_enable()
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#endif /* CONFIG_PRINTK */
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