From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
Calvin Owens <calvinowens@fb.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Hurley <peter@hurleysoftware.com>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: [PATCHv7 7/8] printk: remove zap_locks() function
Date: Tue, 27 Dec 2016 23:16:10 +0900 [thread overview]
Message-ID: <20161227141611.940-8-sergey.senozhatsky@gmail.com> (raw)
In-Reply-To: <20161227141611.940-1-sergey.senozhatsky@gmail.com>
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).
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
kernel/printk/printk.c | 61 --------------------------------------------------
1 file changed, 61 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2dd43ae94c64..1002dfd4ee96 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1556,28 +1556,6 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
}
}
-/*
- * 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)
@@ -1687,17 +1665,13 @@ 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;
@@ -1708,42 +1682,8 @@ 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.
@@ -1786,7 +1726,6 @@ 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);
--
2.11.0
next prev parent reply other threads:[~2016-12-27 14:18 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-27 14:16 [PATCHv7 0/8] printk: use printk_safe to handle printk() recursive calls Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 1/8] printk: use vprintk_func in vprintk() Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 2/8] printk: rename nmi.c and exported api Sergey Senozhatsky
2017-01-04 13:07 ` Petr Mladek
2017-02-01 15:48 ` Steven Rostedt
2017-02-01 15:50 ` Steven Rostedt
2017-02-23 7:50 ` Geert Uytterhoeven
2017-02-23 8:02 ` Sergey Senozhatsky
2017-02-23 9:23 ` Geert Uytterhoeven
2016-12-27 14:16 ` [PATCHv7 3/8] printk: introduce per-cpu safe_print seq buffer Sergey Senozhatsky
2017-01-04 13:31 ` Petr Mladek
2017-01-05 1:01 ` Sergey Senozhatsky
2017-02-01 15:52 ` Steven Rostedt
2016-12-27 14:16 ` [PATCHv7 4/8] printk: always use deferred printk when flush printk_safe lines Sergey Senozhatsky
2017-02-01 16:06 ` Steven Rostedt
2017-02-02 6:05 ` Sergey Senozhatsky
2017-02-02 15:37 ` Petr Mladek
2017-02-02 15:52 ` Petr Mladek
2017-02-03 2:04 ` Sergey Senozhatsky
2017-02-03 11:18 ` Petr Mladek
2017-02-06 1:48 ` Sergey Senozhatsky
2017-02-06 2:08 ` Sergey Senozhatsky
2017-02-06 12:16 ` Petr Mladek
2017-02-06 13:27 ` Steven Rostedt
2017-02-06 16:42 ` Sergey Senozhatsky
2017-02-06 16:55 ` Steven Rostedt
2016-12-27 14:16 ` [PATCHv7 5/8] printk: report lost messages in printk safe/nmi contexts Sergey Senozhatsky
2017-01-04 14:46 ` Petr Mladek
2017-01-05 1:01 ` Sergey Senozhatsky
2017-02-01 16:37 ` Steven Rostedt
2017-02-02 2:02 ` Sergey Senozhatsky
2017-02-02 14:34 ` Steven Rostedt
2017-02-02 16:13 ` Petr Mladek
2017-02-03 1:57 ` Sergey Senozhatsky
2017-02-03 3:13 ` Steven Rostedt
2016-12-27 14:16 ` [PATCHv7 6/8] printk: use printk_safe buffers in printk Sergey Senozhatsky
2017-01-31 17:27 ` Ross Zwisler
2017-02-01 9:06 ` Jan Kara
2017-02-01 9:37 ` Peter Zijlstra
2017-02-01 15:39 ` Petr Mladek
2017-02-01 16:15 ` Peter Zijlstra
2017-02-01 16:41 ` Steven Rostedt
2017-02-02 2:11 ` Sergey Senozhatsky
2017-02-02 9:07 ` Peter Zijlstra
2017-02-02 10:03 ` Sergey Senozhatsky
2017-02-02 15:20 ` Petr Mladek
2017-02-03 2:45 ` Sergey Senozhatsky
2017-02-02 1:59 ` Sergey Senozhatsky
2017-02-01 17:04 ` Steven Rostedt
2017-02-02 2:13 ` Sergey Senozhatsky
2016-12-27 14:16 ` Sergey Senozhatsky [this message]
2016-12-27 14:16 ` [PATCHv7 8/8] printk: convert the rest to printk-safe Sergey Senozhatsky
2017-01-04 16:28 ` Petr Mladek
2017-01-05 1:00 ` Sergey Senozhatsky
2017-01-05 16:58 ` [PATCHv7 0/8] printk: use printk_safe to handle printk() recursive calls Petr Mladek
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