On Mon 28-04-14 14:14:39, Steven Rostedt wrote:
> On Mon, 28 Apr 2014 19:51:39 +0200
> Jan Kara <[email protected]> wrote:
>
> > On Mon 28-04-14 13:43:31, Steven Rostedt wrote:
> > > Things have changed with regard to printk() in linux-next. Now it
> > > appears that lockdep is going haywire over it. I don't understand the
> > > exact reason for the lockdep_off() and lockdep_on() logic that is in
> > > printk(), but it obviously seems to be causing issues with the new
> > > changes.
> > >
> > > Care to take a look?
> > The obvious cause is that I moved lockdep_on() somewhat earlier in
> > vprintk_emit() so lockdep now covers more of printk code. And apparently
> > something is wrong there...
> >
>
> Exactly, and I rather know *exactly* what is wrong before we just start
> throwing patches at the problem and hope it goes away. That's not how
> to solve a software bug.
So I had a look and we are missing mutex_release() in
console_trylock_for_printk() if we don't have a console to print to.
Attached patch should fix the problem.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
>From e8cfbd7ec0f9a820ab38c3ce236940167fa82193 Mon Sep 17 00:00:00 2001
From: Jan Kara <[email protected]>
Date: Mon, 28 Apr 2014 21:09:26 +0200
Subject: [PATCH] printk: Fix lockdep instrumentation of console_sem
Printk calls mutex_acquire() / mutex_release() by hand to instrument
lockdep about console_sem. However in some corner cases the
instrumentation is missing. Fix the problem by creating helper functions
for locking / unlocking console_sem which take care of lockdep
instrumentation as well.
Signed-off-by: Jan Kara <[email protected]>
---
kernel/printk/printk.c | 39 ++++++++++++++++++++++++++++-----------
1 file changed, 28 insertions(+), 11 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 91c554e027c5..bcaab92fe7c0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1877,6 +1877,26 @@ module_param_named(console_suspend, console_suspend_enabled,
MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
" and hibernate operations");
+static inline void down_console_sem(void)
+{
+ down(&console_sem);
+ mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);
+}
+
+static inline int down_trylock_console_sem(void)
+{
+ if (down_trylock(&console_sem))
+ return 1;
+ mutex_acquire(&console_lock_dep_map, 0, 1, _RET_IP_);
+ return 0;
+}
+
+static inline void up_console_sem(void)
+{
+ mutex_release(&console_lock_dep_map, 1, _RET_IP_);
+ up(&console_sem);
+}
+
/**
* suspend_console - suspend the console subsystem
*
@@ -1889,14 +1909,14 @@ void suspend_console(void)
printk("Suspending console(s) (use no_console_suspend to debug)\n");
console_lock();
console_suspended = 1;
- up(&console_sem);
+ up_console_sem();
}
void resume_console(void)
{
if (!console_suspend_enabled)
return;
- down(&console_sem);
+ down_console_sem();
console_suspended = 0;
console_unlock();
}
@@ -1938,12 +1958,11 @@ void console_lock(void)
{
might_sleep();
- down(&console_sem);
+ down_console_sem();
if (console_suspended)
return;
console_locked = 1;
console_may_schedule = 1;
- mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);
}
EXPORT_SYMBOL(console_lock);
@@ -1957,15 +1976,14 @@ EXPORT_SYMBOL(console_lock);
*/
int console_trylock(void)
{
- if (down_trylock(&console_sem))
+ if (down_trylock_console_sem())
return 0;
if (console_suspended) {
- up(&console_sem);
+ up_console_sem();
return 0;
}
console_locked = 1;
console_may_schedule = 0;
- mutex_acquire(&console_lock_dep_map, 0, 1, _RET_IP_);
return 1;
}
EXPORT_SYMBOL(console_trylock);
@@ -2027,7 +2045,7 @@ void console_unlock(void)
bool retry;
if (console_suspended) {
- up(&console_sem);
+ up_console_sem();
return;
}
@@ -2089,7 +2107,6 @@ skip:
local_irq_restore(flags);
}
console_locked = 0;
- mutex_release(&console_lock_dep_map, 1, _RET_IP_);
/* Release the exclusive_console once it is used */
if (unlikely(exclusive_console))
@@ -2097,7 +2114,7 @@ skip:
raw_spin_unlock(&logbuf_lock);
- up(&console_sem);
+ up_console_sem();
/*
* Someone could have filled up the buffer again, so re-check if there's
@@ -2142,7 +2159,7 @@ void console_unblank(void)
* oops_in_progress is set to 1..
*/
if (oops_in_progress) {
- if (down_trylock(&console_sem) != 0)
+ if (down_trylock_console_sem() != 0)
return;
} else
console_lock();
--
1.8.1.4
