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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2016-12-27 23:16:10 +0900
committerPetr Mladek <pmladek@suse.com>2017-02-08 13:54:27 +0100
commit8b1742c9c2071520efacf44e974dc03421360471 (patch)
tree560f6c65d09b8621a3809ecf83831caecb8072a9 /kernel/printk
parentf975237b76827956fe13ecfe993a319158e2c303 (diff)
downloadlinux-8b1742c9c2071520efacf44e974dc03421360471.tar.bz2
printk: remove zap_locks() function
We use printk-safe now which makes printk-recursion detection code in vprintk_emit() unreachable. The tricky thing here is that, apart from detecting and reporting printk recursions, that code also used to zap_locks() in case of panic() from the same CPU. However, zap_locks() does not look to be needed anymore: 1) Since commit 08d78658f393 ("panic: release stale console lock to always get the logbuf printed out") panic flushing of `logbuf' to console ignores the state of `console_sem' by doing panic() console_trylock(); console_unlock(); 2) Since commit cf9b1106c81c ("printk/nmi: flush NMI messages on the system panic") panic attempts to zap the `logbuf_lock' spin_lock to successfully flush nmi messages to `logbuf'. Basically, it seems that we either already do what zap_locks() used to do but in other places or we ignore the state of the lock. The only reaming difference is that we don't re-init the console semaphore in printk_safe_flush_on_panic(), but this is not necessary because we don't call console drivers from printk_safe_flush_on_panic() due to the fact that we are using a deferred printk() version (as was suggested by Petr Mladek). Link: http://lkml.kernel.org/r/20161227141611.940-8-sergey.senozhatsky@gmail.com Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Jan Kara <jack@suse.cz> Cc: Tejun Heo <tj@kernel.org> Cc: Calvin Owens <calvinowens@fb.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Petr Mladek <pmladek@suse.com>
Diffstat (limited to 'kernel/printk')
-rw-r--r--kernel/printk/printk.c61
1 files changed, 0 insertions, 61 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f426a2b12a9b..e17d384f8c6b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1557,28 +1557,6 @@ static void call_console_drivers(int level,
}
}
-/*
- * Zap console related locks when oopsing.
- * To leave time for slow consoles to print a full oops,
- * only zap at most once every 30 seconds.
- */
-static void zap_locks(void)
-{
- static unsigned long oops_timestamp;
-
- if (time_after_eq(jiffies, oops_timestamp) &&
- !time_after(jiffies, oops_timestamp + 30 * HZ))
- return;
-
- oops_timestamp = jiffies;
-
- debug_locks_off();
- /* If a crash is occurring, make sure we can't deadlock */
- raw_spin_lock_init(&logbuf_lock);
- /* And make sure that we print immediately */
- sema_init(&console_sem, 1);
-}
-
int printk_delay_msec __read_mostly;
static inline void printk_delay(void)
@@ -1688,17 +1666,13 @@ asmlinkage int vprintk_emit(int facility, int level,
const char *dict, size_t dictlen,
const char *fmt, va_list args)
{
- static bool recursion_bug;
static char textbuf[LOG_LINE_MAX];
char *text = textbuf;
size_t text_len = 0;
enum log_flags lflags = 0;
unsigned long flags;
- int this_cpu;
int printed_len = 0;
bool in_sched = false;
- /* cpu currently holding logbuf_lock in this function */
- static unsigned int logbuf_cpu = UINT_MAX;
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
@@ -1709,42 +1683,8 @@ asmlinkage int vprintk_emit(int facility, int level,
printk_delay();
printk_safe_enter_irqsave(flags);
- this_cpu = smp_processor_id();
-
- /*
- * Ouch, printk recursed into itself!
- */
- if (unlikely(logbuf_cpu == this_cpu)) {
- /*
- * If a crash is occurring during printk() on this CPU,
- * then try to get the crash message out but make sure
- * we can't deadlock. Otherwise just return to avoid the
- * recursion and return - but flag the recursion so that
- * it can be printed at the next appropriate moment:
- */
- if (!oops_in_progress && !lockdep_recursing(current)) {
- recursion_bug = true;
- printk_safe_exit_irqrestore(flags);
- return 0;
- }
- zap_locks();
- }
-
/* This stops the holder of console_sem just where we want him */
raw_spin_lock(&logbuf_lock);
- logbuf_cpu = this_cpu;
-
- if (unlikely(recursion_bug)) {
- static const char recursion_msg[] =
- "BUG: recent printk recursion!";
-
- recursion_bug = false;
- /* emit KERN_CRIT message */
- printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
- NULL, 0, recursion_msg,
- strlen(recursion_msg));
- }
-
/*
* The printf needs to come first; we need the syslog
* prefix which might be passed-in as a parameter.
@@ -1787,7 +1727,6 @@ asmlinkage int vprintk_emit(int facility, int level,
printed_len += log_output(facility, level, lflags, dict, dictlen, text, text_len);
- logbuf_cpu = UINT_MAX;
raw_spin_unlock(&logbuf_lock);
printk_safe_exit_irqrestore(flags);