diff options
Diffstat (limited to 'kernel/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 67 |
1 files changed, 62 insertions, 5 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 2ce8826f1053..e79439134978 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -48,6 +48,7 @@ #include <linux/uio.h> #include <asm/uaccess.h> +#include <asm-generic/sections.h> #define CREATE_TRACE_POINTS #include <trace/events/printk.h> @@ -1660,7 +1661,7 @@ asmlinkage int vprintk_emit(int facility, int level, const char *dict, size_t dictlen, const char *fmt, va_list args) { - static int recursion_bug; + static bool recursion_bug; static char textbuf[LOG_LINE_MAX]; char *text = textbuf; size_t text_len = 0; @@ -1696,7 +1697,7 @@ asmlinkage int vprintk_emit(int facility, int level, * it can be printed at the next appropriate moment: */ if (!oops_in_progress && !lockdep_recursing(current)) { - recursion_bug = 1; + recursion_bug = true; local_irq_restore(flags); return 0; } @@ -1711,7 +1712,7 @@ asmlinkage int vprintk_emit(int facility, int level, static const char recursion_msg[] = "BUG: recent printk recursion!"; - recursion_bug = 0; + recursion_bug = false; /* emit KERN_CRIT message */ printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0, NULL, 0, recursion_msg, @@ -2233,13 +2234,24 @@ void console_unlock(void) static u64 seen_seq; unsigned long flags; bool wake_klogd = false; - bool retry; + bool do_cond_resched, retry; if (console_suspended) { up_console_sem(); return; } + /* + * Console drivers are called under logbuf_lock, so + * @console_may_schedule should be cleared before; however, we may + * end up dumping a lot of lines, for example, if called from + * console registration path, and should invoke cond_resched() + * between lines if allowable. Not doing so can cause a very long + * scheduling stall on a slow console leading to RCU stall and + * softlockup warnings which exacerbate the issue with more + * messages practically incapacitating the system. + */ + do_cond_resched = console_may_schedule; console_may_schedule = 0; /* flush buffered message fragment immediately to console */ @@ -2311,6 +2323,9 @@ skip: call_console_drivers(level, ext_text, ext_len, text, len); start_critical_timings(); local_irq_restore(flags); + + if (do_cond_resched) + cond_resched(); } console_locked = 0; @@ -2378,6 +2393,25 @@ void console_unblank(void) console_unlock(); } +/** + * console_flush_on_panic - flush console content on panic + * + * Immediately output all pending messages no matter what. + */ +void console_flush_on_panic(void) +{ + /* + * If someone else is holding the console lock, trylock will fail + * and may_schedule may be set. Ignore and proceed to unlock so + * that messages are flushed out. As this can be called from any + * context and we don't want to get preempted while flushing, + * ensure may_schedule is cleared. + */ + console_trylock(); + console_may_schedule = 0; + console_unlock(); +} + /* * Return the console tty driver structure and its associated index */ @@ -2658,13 +2692,36 @@ int unregister_console(struct console *console) } EXPORT_SYMBOL(unregister_console); +/* + * Some boot consoles access data that is in the init section and which will + * be discarded after the initcalls have been run. To make sure that no code + * will access this data, unregister the boot consoles in a late initcall. + * + * If for some reason, such as deferred probe or the driver being a loadable + * module, the real console hasn't registered yet at this point, there will + * be a brief interval in which no messages are logged to the console, which + * makes it difficult to diagnose problems that occur during this time. + * + * To mitigate this problem somewhat, only unregister consoles whose memory + * intersects with the init section. Note that code exists elsewhere to get + * rid of the boot console as soon as the proper console shows up, so there + * won't be side-effects from postponing the removal. + */ static int __init printk_late_init(void) { struct console *con; for_each_console(con) { if (!keep_bootcon && con->flags & CON_BOOT) { - unregister_console(con); + /* + * Make sure to unregister boot consoles whose data + * resides in the init section before the init section + * is discarded. Boot consoles whose data will stick + * around will automatically be unregistered when the + * proper console replaces them. + */ + if (init_section_intersects(con, sizeof(*con))) + unregister_console(con); } } hotcpu_notifier(console_cpu_notify, 0); |