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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 08d78658f3 ("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 cf9b1106c8 ("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>
This commit is contained in:
Sergey Senozhatsky 2016-12-27 23:16:10 +09:00 committed by Petr Mladek
parent f975237b76
commit 8b1742c9c2
1 changed files with 0 additions and 61 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
kernel/printk/printk.c
View File

@ -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);