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printk: refactor and rework printing logic
Refactor/rework printing logic in order to prepare for moving to threaded console printing. - Move @console_seq into struct console so that the current "position" of each console can be tracked individually. - Move @console_dropped into struct console so that the current drop count of each console can be tracked individually. - Modify printing logic so that each console independently loads, prepares, and prints its next record. - Remove exclusive_console logic. Since console positions are handled independently, replaying past records occurs naturally. - Update the comments explaining why preemption is disabled while printing from printk() context. With these changes, there is a change in behavior: the console replaying the log (formerly exclusive console) will no longer block other consoles. New messages appear on the other consoles while the newly added console is still replaying. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220421212250.565456-10-john.ogness@linutronix.de
This commit is contained in:
John Ogness
Petr Mladek
parent
1fc0ca9e0d
commit
a699449bb1
@ -151,6 +151,8 @@ struct console {
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int cflag;
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uint ispeed;
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uint ospeed;
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u64 seq;
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unsigned long dropped;
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void *data;
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struct console *next;
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};
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@ -280,11 +280,6 @@ static bool panic_in_progress(void)
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*/
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static int console_locked, console_suspended;
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/*
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* If exclusive_console is non-NULL then only this console is to be printed to.
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*/
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static struct console *exclusive_console;
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/*
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* Array of consoles built from command line options (console=)
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*/
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@ -374,12 +369,6 @@ static u64 syslog_seq;
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static size_t syslog_partial;
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static bool syslog_time;
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/* All 3 protected by @console_sem. */
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/* the next printk record to write to the console */
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static u64 console_seq;
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static u64 exclusive_console_stop_seq;
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static unsigned long console_dropped;
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struct latched_seq {
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seqcount_latch_t latch;
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u64 val[2];
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@ -1933,47 +1922,26 @@ static int console_trylock_spinning(void)
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}
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/*
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* Call the console drivers, asking them to write out
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* log_buf[start] to log_buf[end - 1].
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* The console_lock must be held.
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* Call the specified console driver, asking it to write out the specified
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* text and length. For non-extended consoles, if any records have been
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* dropped, a dropped message will be written out first.
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*/
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static void call_console_drivers(const char *ext_text, size_t ext_len,
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const char *text, size_t len)
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static void call_console_driver(struct console *con, const char *text, size_t len)
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{
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static char dropped_text[64];
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size_t dropped_len = 0;
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struct console *con;
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size_t dropped_len;
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trace_console_rcuidle(text, len);
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if (!console_drivers)
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return;
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if (console_dropped) {
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if (con->dropped && !(con->flags & CON_EXTENDED)) {
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dropped_len = snprintf(dropped_text, sizeof(dropped_text),
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"** %lu printk messages dropped **\n",
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console_dropped);
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console_dropped = 0;
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con->dropped);
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con->dropped = 0;
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con->write(con, dropped_text, dropped_len);
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}
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for_each_console(con) {
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if (exclusive_console && con != exclusive_console)
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continue;
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if (!(con->flags & CON_ENABLED))
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continue;
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if (!con->write)
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continue;
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if (!cpu_online(smp_processor_id()) &&
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!(con->flags & CON_ANYTIME))
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continue;
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if (con->flags & CON_EXTENDED)
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con->write(con, ext_text, ext_len);
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else {
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if (dropped_len)
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con->write(con, dropped_text, dropped_len);
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con->write(con, text, len);
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}
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}
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con->write(con, text, len);
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}
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/*
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@ -2283,15 +2251,18 @@ asmlinkage int vprintk_emit(int facility, int level,
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/* If called from the scheduler, we can not call up(). */
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if (!in_sched) {
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/*
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* Disable preemption to avoid being preempted while holding
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* console_sem which would prevent anyone from printing to
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* console
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* The caller may be holding system-critical or
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* timing-sensitive locks. Disable preemption during
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* printing of all remaining records to all consoles so that
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* this context can return as soon as possible. Hopefully
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* another printk() caller will take over the printing.
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*/
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preempt_disable();
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/*
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* Try to acquire and then immediately release the console
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* semaphore. The release will print out buffers and wake up
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* /dev/kmsg and syslog() users.
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* semaphore. The release will print out buffers. With the
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* spinning variant, this context tries to take over the
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* printing from another printing context.
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*/
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if (console_trylock_spinning())
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console_unlock();
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@ -2329,11 +2300,9 @@ EXPORT_SYMBOL(_printk);
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#define prb_read_valid(rb, seq, r) false
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#define prb_first_valid_seq(rb) 0
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#define prb_next_seq(rb) 0
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static u64 syslog_seq;
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static u64 console_seq;
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static u64 exclusive_console_stop_seq;
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static unsigned long console_dropped;
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static size_t record_print_text(const struct printk_record *r,
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bool syslog, bool time)
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@ -2350,8 +2319,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
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struct dev_printk_info *dev_info) { return 0; }
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static void console_lock_spinning_enable(void) { }
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static int console_lock_spinning_disable_and_check(void) { return 0; }
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static void call_console_drivers(const char *ext_text, size_t ext_len,
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const char *text, size_t len) {}
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static void call_console_driver(struct console *con, const char *text, size_t len) { }
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static bool suppress_message_printing(int level) { return false; }
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#endif /* CONFIG_PRINTK */
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@ -2621,22 +2589,6 @@ int is_console_locked(void)
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}
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EXPORT_SYMBOL(is_console_locked);
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/*
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* Check if we have any console that is capable of printing while cpu is
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* booting or shutting down. Requires console_sem.
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*/
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static int have_callable_console(void)
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{
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struct console *con;
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for_each_console(con)
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if ((con->flags & CON_ENABLED) &&
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(con->flags & CON_ANYTIME))
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return 1;
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return 0;
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}
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/*
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* Return true when this CPU should unlock console_sem without pushing all
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* messages to the console. This reduces the chance that the console is
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@ -2657,15 +2609,182 @@ static bool abandon_console_lock_in_panic(void)
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}
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/*
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* Can we actually use the console at this time on this cpu?
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* Check if the given console is currently capable and allowed to print
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* records.
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*
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* Console drivers may assume that per-cpu resources have been allocated. So
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* unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
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* call them until this CPU is officially up.
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* Requires the console_lock.
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*/
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static inline int can_use_console(void)
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static inline bool console_is_usable(struct console *con)
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{
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return cpu_online(raw_smp_processor_id()) || have_callable_console();
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if (!(con->flags & CON_ENABLED))
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return false;
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if (!con->write)
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return false;
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/*
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* Console drivers may assume that per-cpu resources have been
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* allocated. So unless they're explicitly marked as being able to
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* cope (CON_ANYTIME) don't call them until this CPU is officially up.
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*/
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if (!cpu_online(raw_smp_processor_id()) &&
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!(con->flags & CON_ANYTIME))
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return false;
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return true;
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}
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static void __console_unlock(void)
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{
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console_locked = 0;
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up_console_sem();
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}
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/*
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* Print one record for the given console. The record printed is whatever
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* record is the next available record for the given console.
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*
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* @handover will be set to true if a printk waiter has taken over the
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* console_lock, in which case the caller is no longer holding the
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* console_lock. Otherwise it is set to false.
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*
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* Returns false if the given console has no next record to print, otherwise
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* true.
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*
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* Requires the console_lock.
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*/
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static bool console_emit_next_record(struct console *con, bool *handover)
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{
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static char ext_text[CONSOLE_EXT_LOG_MAX];
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static char text[CONSOLE_LOG_MAX];
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static int panic_console_dropped;
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struct printk_info info;
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struct printk_record r;
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unsigned long flags;
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char *write_text;
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size_t len;
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prb_rec_init_rd(&r, &info, text, sizeof(text));
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*handover = false;
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if (!prb_read_valid(prb, con->seq, &r))
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return false;
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if (con->seq != r.info->seq) {
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con->dropped += r.info->seq - con->seq;
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con->seq = r.info->seq;
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if (panic_in_progress() && panic_console_dropped++ > 10) {
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suppress_panic_printk = 1;
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pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
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}
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}
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/* Skip record that has level above the console loglevel. */
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if (suppress_message_printing(r.info->level)) {
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con->seq++;
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goto skip;
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}
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if (con->flags & CON_EXTENDED) {
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write_text = &ext_text[0];
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len = info_print_ext_header(ext_text, sizeof(ext_text), r.info);
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len += msg_print_ext_body(ext_text + len, sizeof(ext_text) - len,
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&r.text_buf[0], r.info->text_len, &r.info->dev_info);
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} else {
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write_text = &text[0];
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len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
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}
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/*
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* While actively printing out messages, if another printk()
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* were to occur on another CPU, it may wait for this one to
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* finish. This task can not be preempted if there is a
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* waiter waiting to take over.
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*
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* Interrupts are disabled because the hand over to a waiter
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* must not be interrupted until the hand over is completed
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* (@console_waiter is cleared).
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*/
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printk_safe_enter_irqsave(flags);
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console_lock_spinning_enable();
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stop_critical_timings(); /* don't trace print latency */
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call_console_driver(con, write_text, len);
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start_critical_timings();
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con->seq++;
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*handover = console_lock_spinning_disable_and_check();
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printk_safe_exit_irqrestore(flags);
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skip:
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return true;
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}
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/*
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* Print out all remaining records to all consoles.
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*
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* @do_cond_resched is set by the caller. It can be true only in schedulable
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* context.
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*
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* @next_seq is set to the sequence number after the last available record.
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* The value is valid only when this function returns true. It means that all
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* usable consoles are completely flushed.
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*
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* @handover will be set to true if a printk waiter has taken over the
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* console_lock, in which case the caller is no longer holding the
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* console_lock. Otherwise it is set to false.
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*
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* Returns true when there was at least one usable console and all messages
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* were flushed to all usable consoles. A returned false informs the caller
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* that everything was not flushed (either there were no usable consoles or
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* another context has taken over printing or it is a panic situation and this
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* is not the panic CPU). Regardless the reason, the caller should assume it
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* is not useful to immediately try again.
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*
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* Requires the console_lock.
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*/
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static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
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{
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bool any_usable = false;
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struct console *con;
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bool any_progress;
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*next_seq = 0;
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*handover = false;
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do {
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any_progress = false;
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for_each_console(con) {
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bool progress;
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if (!console_is_usable(con))
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continue;
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any_usable = true;
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progress = console_emit_next_record(con, handover);
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if (*handover)
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return false;
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/* Track the next of the highest seq flushed. */
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if (con->seq > *next_seq)
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*next_seq = con->seq;
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if (!progress)
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continue;
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any_progress = true;
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/* Allow panic_cpu to take over the consoles safely. */
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if (abandon_console_lock_in_panic())
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return false;
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if (do_cond_resched)
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cond_resched();
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}
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} while (any_progress);
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return any_usable;
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}
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/**
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@ -2678,28 +2797,20 @@ static inline int can_use_console(void)
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* by printk(). If this is the case, console_unlock(); emits
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* the output prior to releasing the lock.
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*
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* If there is output waiting, we wake /dev/kmsg and syslog() users.
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*
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* console_unlock(); may be called from any context.
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*/
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void console_unlock(void)
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{
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static char ext_text[CONSOLE_EXT_LOG_MAX];
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static char text[CONSOLE_LOG_MAX];
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static int panic_console_dropped;
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unsigned long flags;
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bool do_cond_resched, retry;
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struct printk_info info;
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struct printk_record r;
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u64 __maybe_unused next_seq;
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bool do_cond_resched;
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bool handover;
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bool flushed;
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u64 next_seq;
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if (console_suspended) {
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up_console_sem();
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return;
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}
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prb_rec_init_rd(&r, &info, text, sizeof(text));
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/*
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* Console drivers are called with interrupts disabled, so
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* @console_may_schedule should be cleared before; however, we may
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@ -2708,125 +2819,34 @@ void console_unlock(void)
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* between lines if allowable. Not doing so can cause a very long
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* scheduling stall on a slow console leading to RCU stall and
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* softlockup warnings which exacerbate the issue with more
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* messages practically incapacitating the system.
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*
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* console_trylock() is not able to detect the preemptive
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* context reliably. Therefore the value must be stored before
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* and cleared after the "again" goto label.
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* messages practically incapacitating the system. Therefore, create
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* a local to use for the printing loop.
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*/
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do_cond_resched = console_may_schedule;
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again:
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console_may_schedule = 0;
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/*
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* We released the console_sem lock, so we need to recheck if
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* cpu is online and (if not) is there at least one CON_ANYTIME
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* console.
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*/
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if (!can_use_console()) {
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console_locked = 0;
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up_console_sem();
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return;
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}
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do {
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console_may_schedule = 0;
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for (;;) {
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size_t ext_len = 0;
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int handover;
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size_t len;
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skip:
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if (!prb_read_valid(prb, console_seq, &r))
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break;
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if (console_seq != r.info->seq) {
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console_dropped += r.info->seq - console_seq;
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console_seq = r.info->seq;
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if (panic_in_progress() && panic_console_dropped++ > 10) {
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suppress_panic_printk = 1;
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pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
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}
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}
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if (suppress_message_printing(r.info->level)) {
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/*
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* Skip record we have buffered and already printed
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* directly to the console when we received it, and
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* record that has level above the console loglevel.
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*/
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console_seq++;
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goto skip;
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}
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/* Output to all consoles once old messages replayed. */
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if (unlikely(exclusive_console &&
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console_seq >= exclusive_console_stop_seq)) {
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exclusive_console = NULL;
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}
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flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
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if (!handover)
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__console_unlock();
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/*
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* Handle extended console text first because later
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* record_print_text() will modify the record buffer in-place.
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* Abort if there was a failure to flush all messages to all
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* usable consoles. Either it is not possible to flush (in
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* which case it would be an infinite loop of retrying) or
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* another context has taken over printing.
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*/
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if (nr_ext_console_drivers) {
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ext_len = info_print_ext_header(ext_text,
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sizeof(ext_text),
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r.info);
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ext_len += msg_print_ext_body(ext_text + ext_len,
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sizeof(ext_text) - ext_len,
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&r.text_buf[0],
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r.info->text_len,
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&r.info->dev_info);
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}
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len = record_print_text(&r,
|
||||
console_msg_format & MSG_FORMAT_SYSLOG,
|
||||
printk_time);
|
||||
console_seq++;
|
||||
|
||||
/*
|
||||
* While actively printing out messages, if another printk()
|
||||
* were to occur on another CPU, it may wait for this one to
|
||||
* finish. This task can not be preempted if there is a
|
||||
* waiter waiting to take over.
|
||||
*
|
||||
* Interrupts are disabled because the hand over to a waiter
|
||||
* must not be interrupted until the hand over is completed
|
||||
* (@console_waiter is cleared).
|
||||
*/
|
||||
printk_safe_enter_irqsave(flags);
|
||||
console_lock_spinning_enable();
|
||||
|
||||
stop_critical_timings(); /* don't trace print latency */
|
||||
call_console_drivers(ext_text, ext_len, text, len);
|
||||
start_critical_timings();
|
||||
|
||||
handover = console_lock_spinning_disable_and_check();
|
||||
printk_safe_exit_irqrestore(flags);
|
||||
if (handover)
|
||||
return;
|
||||
|
||||
/* Allow panic_cpu to take over the consoles safely */
|
||||
if (abandon_console_lock_in_panic())
|
||||
if (!flushed)
|
||||
break;
|
||||
|
||||
if (do_cond_resched)
|
||||
cond_resched();
|
||||
}
|
||||
|
||||
/* Get consistent value of the next-to-be-used sequence number. */
|
||||
next_seq = console_seq;
|
||||
|
||||
console_locked = 0;
|
||||
up_console_sem();
|
||||
|
||||
/*
|
||||
* Someone could have filled up the buffer again, so re-check if there's
|
||||
* something to flush. In case we cannot trylock the console_sem again,
|
||||
* there's a new owner and the console_unlock() from them will do the
|
||||
* flush, no worries.
|
||||
*/
|
||||
retry = prb_read_valid(prb, next_seq, NULL);
|
||||
if (retry && !abandon_console_lock_in_panic() && console_trylock())
|
||||
goto again;
|
||||
/*
|
||||
* Some context may have added new records after
|
||||
* console_flush_all() but before unlocking the console.
|
||||
* Re-check if there is a new record to flush. If the trylock
|
||||
* fails, another context is already handling the printing.
|
||||
*/
|
||||
} while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
|
||||
}
|
||||
EXPORT_SYMBOL(console_unlock);
|
||||
|
||||
@ -2886,8 +2906,14 @@ void console_flush_on_panic(enum con_flush_mode mode)
|
||||
console_trylock();
|
||||
console_may_schedule = 0;
|
||||
|
||||
if (mode == CONSOLE_REPLAY_ALL)
|
||||
console_seq = prb_first_valid_seq(prb);
|
||||
if (mode == CONSOLE_REPLAY_ALL) {
|
||||
struct console *c;
|
||||
u64 seq;
|
||||
|
||||
seq = prb_first_valid_seq(prb);
|
||||
for_each_console(c)
|
||||
c->seq = seq;
|
||||
}
|
||||
console_unlock();
|
||||
}
|
||||
|
||||
@ -3127,26 +3153,15 @@ void register_console(struct console *newcon)
|
||||
if (newcon->flags & CON_EXTENDED)
|
||||
nr_ext_console_drivers++;
|
||||
|
||||
newcon->dropped = 0;
|
||||
if (newcon->flags & CON_PRINTBUFFER) {
|
||||
/*
|
||||
* console_unlock(); will print out the buffered messages
|
||||
* for us.
|
||||
*
|
||||
* We're about to replay the log buffer. Only do this to the
|
||||
* just-registered console to avoid excessive message spam to
|
||||
* the already-registered consoles.
|
||||
*
|
||||
* Set exclusive_console with disabled interrupts to reduce
|
||||
* race window with eventual console_flush_on_panic() that
|
||||
* ignores console_lock.
|
||||
*/
|
||||
exclusive_console = newcon;
|
||||
exclusive_console_stop_seq = console_seq;
|
||||
|
||||
/* Get a consistent copy of @syslog_seq. */
|
||||
mutex_lock(&syslog_lock);
|
||||
console_seq = syslog_seq;
|
||||
newcon->seq = syslog_seq;
|
||||
mutex_unlock(&syslog_lock);
|
||||
} else {
|
||||
/* Begin with next message. */
|
||||
newcon->seq = prb_next_seq(prb);
|
||||
}
|
||||
console_unlock();
|
||||
console_sysfs_notify();
|
||||
|
||||
Loading…
Reference in New Issue
Block a user