printk: make printk more robust by not allowing recursion
make printk more robust by allowing recursion only if there's a crash going on. Also add recursion detection. I've tested it with an artificially injected printk recursion - instead of a lockup or spontaneous reboot or other crash, the output was a well controlled: [ 41.057335] SysRq : <2>BUG: recent printk recursion! [ 41.057335] loglevel0-8 reBoot Crashdump show-all-locks(D) tErm Full kIll saK showMem Nice powerOff showPc show-all-timers(Q) unRaw Sync showTasks Unmount shoW-blocked-tasks also do all this printk-debug logic with irqs disabled. Signed-off-by: Ingo Molnar <mingo@elte.hu> Reviewed-by: Nick Piggin <npiggin@suse.de>
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@ -628,30 +628,57 @@ asmlinkage int printk(const char *fmt, ...)
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/* cpu currently holding logbuf_lock */
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/* cpu currently holding logbuf_lock */
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static volatile unsigned int printk_cpu = UINT_MAX;
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static volatile unsigned int printk_cpu = UINT_MAX;
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const char printk_recursion_bug_msg [] =
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KERN_CRIT "BUG: recent printk recursion!\n";
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static int printk_recursion_bug;
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asmlinkage int vprintk(const char *fmt, va_list args)
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asmlinkage int vprintk(const char *fmt, va_list args)
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{
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{
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unsigned long flags;
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int printed_len;
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char *p;
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static char printk_buf[1024];
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static int log_level_unknown = 1;
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static int log_level_unknown = 1;
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static char printk_buf[1024];
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unsigned long flags;
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int printed_len = 0;
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int this_cpu;
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char *p;
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boot_delay_msec();
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boot_delay_msec();
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preempt_disable();
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preempt_disable();
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if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
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/* If a crash is occurring during printk() on this CPU,
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* make sure we can't deadlock */
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zap_locks();
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/* This stops the holder of console_sem just where we want him */
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/* This stops the holder of console_sem just where we want him */
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raw_local_irq_save(flags);
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raw_local_irq_save(flags);
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this_cpu = smp_processor_id();
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/*
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* Ouch, printk recursed into itself!
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*/
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if (unlikely(printk_cpu == this_cpu)) {
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/*
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* If a crash is occurring during printk() on this CPU,
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* then try to get the crash message out but make sure
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* we can't deadlock. Otherwise just return to avoid the
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* recursion and return - but flag the recursion so that
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* it can be printed at the next appropriate moment:
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*/
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if (!oops_in_progress) {
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printk_recursion_bug = 1;
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goto out_restore_irqs;
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}
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zap_locks();
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}
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lockdep_off();
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lockdep_off();
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spin_lock(&logbuf_lock);
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spin_lock(&logbuf_lock);
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printk_cpu = smp_processor_id();
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printk_cpu = this_cpu;
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if (printk_recursion_bug) {
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printk_recursion_bug = 0;
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strcpy(printk_buf, printk_recursion_bug_msg);
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printed_len = sizeof(printk_recursion_bug_msg);
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}
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/* Emit the output into the temporary buffer */
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/* Emit the output into the temporary buffer */
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printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
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printed_len += vscnprintf(printk_buf + printed_len,
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sizeof(printk_buf), fmt, args);
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/*
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/*
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* Copy the output into log_buf. If the caller didn't provide
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* Copy the output into log_buf. If the caller didn't provide
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@ -744,6 +771,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
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printk_cpu = UINT_MAX;
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printk_cpu = UINT_MAX;
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spin_unlock(&logbuf_lock);
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spin_unlock(&logbuf_lock);
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lockdep_on();
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lockdep_on();
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out_restore_irqs:
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raw_local_irq_restore(flags);
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raw_local_irq_restore(flags);
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}
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}
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